This slowly growing list of nearly 250 plant galls includes all those California gall inducers that had at least 8 observations in iNaturalist's Galls of California project in August 2020 except for oak galls and galls caused by fungi, mistletoes, or bacteria. You'll find some oak, fungus, mistletoe, and bacteria galls listed, but the coverage is spotty. Root galls are omitted. For oak gall ID, I recommend perusing Joyce Gross's excellent photo-guide and checking the entry California Oak Galls in this journal to see which oaks host which galls and pick up ID pointers for a few of the oak galls.

A few incompletely described species that have been identified to the genus level are included here too, but California has a lot of galls that remain undescribed.

This somewhat idiosyncratic list was begun in mid-2020 to complement, rather than replace, Ron Russo's impressive, 2006 "Field Guide to Plant Galls of California and Other Western States." Accordingly, some galls covered in that book, which was succeeded in April 2021 by Russo's Plant Galls of the Western United States, have been intentionally omitted, out of a sense of indebtedness to the person who has done so much to advance our knowledge of gall-inducing species in this part of the world. If you want a visual guide showing all the scientifically described galls iNaturalist members have found in California, just pull up the species list from the Galls of California project.

How to Use This List
This list is alphabetized by plants' scientific names to keep related plant species together. To search the list by a host plant's common name, enter [cntrl]F and type the common name. [BTW, for some species for which we had few or no observations when the species was added to the list, the entry ends with the # of California iNat obs[ervations] of the gall--roughly as of then--and where they occurred--e.g., SFBA, meaning SF Bay Area.]

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Abies sp--Fir: Fir Broom Rust (Melampsorella caryophyllacearum) See USDA info sheet and PNW Handbook entry. Causes witches' brooms, sometimes large, with yellow needles that drop off in the fall. [9 obs]

Acer negundo--Boxelder : Box elder pouch gall mite (Aceria negundi) pouch galls on leaves [2 obs SFBA]

Adenostoma fasciculatum--Chamise: Eriophyes adenostomae [Synonym: Phytoptus adenostomae] Mite-induced leaf "pouch" gall that looks like a conglomeration of puckered beads attached to the slender leaf [8 obs SFBA]

Aesculus californica—California buckeye: Taphrina aesculi leaf blister; witches’ broom [3 obs SFBA]

Alnus—Alder:
--Alder Leaf Gall Mite (Eriophyes laevis) Small, often colorful hemispheric-to-round galls on top of leaf; same but hemispheric-to-flat on underside. For closeup photos see Bladmineers photos [29 Calif. obs]
-- Alder Leaf Gall Mite (Acalitus brevitarsus) Leaf blister gall [3 obs SFBA & N]
--Leaf Fold Gall (Dasineura sp.) Undescribed leaf gall induced by midge [Note that feeding by the Woolly Alder Aphid (Prociphilus tessellatus) can also cause leaf folds in alders; look for white wool as evidence of aphids]
-- Western American Alder Tongue Gall (Taphrina occidentalis) [82 obs Big Sur and north to border]
--Catkin Gall (Dasineura) Another undescribed midge gall

Aloe sp & other Asphodelaceae: Aloe gall mite (Aceria aloinis) photos These tiny mites can produce large formations on the plants. [22 obs SoCal & 1 in SF]

Ambrosia--Ragweeds:
--Contarinia partheniicola Per Gagne 1975, "forms whitish, woolly cupulate [cup-shaped] galls" on Ambrosia spp. & Mariola that are 5-8mm x 4-5mm. They occur singly or in small groups on axillary buds, leaves, staminate florets, and the rachis and have been collected from five species of Ambrosia in SoCal. See BugGuide photos [2 obs]
--Asphondylia ambrosiae According to Gagne 1975, this midge "forms fuzzy, globose bud galls on Ambrosia spp." See BugGuide photo [not yet found W of TX]

Ambrosia psilostachya—Western ragweed: Ragweed Gall Mite (Aceria boycei) Leaf blister [none of 89 CA obs are N of Sta Barbara]

Ambrosia chenopodiifolia --San Diego Bur-Sage: Aceria franseriae Bead galls described by Wilson & Oldfield
Amelanchier--Serviceberries:
--Blaesodiplosis Undescribed species of this midge genus induce a variety of leaf galls on serviceberries. See BugGuide for one example.
--Taphrina amelanchieri Causes witches' brooms
--Gymnosporangium inconspicuum See photo at bottom of page. "Horns" of whitish to yellow-orange rust stick out of fruit. Uncommon in California; common in some SW states. [0 obs]
--Russo reports finding an undescribed aphid that induces leaf-roll galls on serviceberry.

Amsinckia sp--Fiddleneck:
-- Schizomyia macrofila See https://bugguide.net/node/view/1042524 midge-induced flower bud gall. According to Pantone et al. (1985) "any aboveground portion of the weed may form midge galls containing one or more orange-colored larvae." Care must be taken to distinguish between this and the similar nematode gall-see next entry.
-- Fiddleneck Gall Nematode (Anguina amsinckia) large gall replaces flower head preferential galling of the lowermost flowers (Fl-F6) within a given inflorescence. See http://calag.ucanr.edu/archive/?type=pdf&article=ca.v039n07p4 and https://pdfs.semanticscholar.org/df9f/c0132f7f45ed095f2466e765d2aae3c6728b.pdf

Arbutus menziesii--Pacific madrone:
--Exobasidium (Exobasidium) Marianne Elliott writes that "Blister blight (Exobasidium [ ]) forms pinkish blisterlike galls that" can distort and twist the leaves of A. menziesii and can make the fruit "turn red and swell." [pg. 58] The tree is also host to a variety of other pathogenic fungi. See pages 28 to end of this WSU web publication
--Neofusicoccum arbuti Causes a variety of cankers (dead areas) on madrone trees along the Pacific coast that can kill the trees. Often takes the form of a large sunken dead area on the trunk with a raised area of "callus" around it as the tree attempts to wall off the fungus. More info here--page 39 in particular. [Since the raised area is the tree's natural response to attack, this is a pseudogall, not a true gall.] [18 obs]

Arctostaphylos—Manzanita: Exobasidium arctostaphyli For individual leaf galls on Arctostaphylos caused by the Exobasidium fungus.

Arctostaphylos—Manzanita: Manzanita Leafgall Aphid (Tamalia coweni) Pod-shaped leaf gall at leaf edge about twice as long as it is wide. This aphid also causes roundish flower galls and sometimes midrib galls, but this occurs only with A. patula and perhaps some other species. For help distinguishing Tamalia galls from the surprisingly similar Cowberry Redleaf fungal galls, see this UC-IPM webpage. See also note below. In addition, it is not clear whether Tamalia milleri, a new species that Kanturski & Wieczorek 2015 describe from museum specimens, introduces galls on its host, A. columbiana (hairy manzanita).

Arctostaphylos pringlei--Pringle's manzanita: Tamalia dicksoni Galls are very similar to Tamalia coweni galls, so galls on this plant should probably be attributed to Tamalia spp. Although this UC-IPM webpage states that T. dicksoni galls other species of manzanita as well, Aphids on the World's Plants, based, I believe, on a more recent article, lists it as not being known to gall more than this one species. San Bernardino Mountains.

Artemisia californica—California sagebrush:
-- Sagebrush Woolly Stem Gall Midge (Rhopalomyia floccosa) Look for white "cotton balls" along the stem.
-- California Sagebrush Gall Mite (Aceria paracalifornica)

Artemisia ludoviciana--Silver wormwood: Eutreta simplex. Terminal bud gall formed on very short shoots very near ground level. The gray-green galls are subovoidal in shape and hairy, and have leaves emerging from them. For photos see p. 35 of Goeden 1990 article. Recorded from SoCal on steep slopes shaded by conifers.

Artemisia douglasiana--California mugwort: Aceria abalis Bumps on leaves; white erineum pockets on underside [1 obs--San Diego]

Artemisia tridentata--Great Basin sagebrush:This one species hosts at least 28 different midge-induced galls, plus a few other types of galls. Some additional info [in a 7-species chart and a footnote] on p. 4 of Nevada NPS.
--Rhopalomyia cramboides Rosette gall with outer "rose petals" as wide as long, but inner ones more linear [2 obs]
-- Sponge Gall Midge (Rhopalomyia pomum)
-- Woolly Bud Gall Midge (Rhopalomyia medusirrasa) Info & photos at https://thenatureniche.com/2013/07/01/wooly-bud-gall-midge/ See discussion re distinguishing this from R. medusa.
--Sagebrush Plum Gall Midge (Rhopalomyia calvipomum)
--Eutreta diana Stem gall; can occur on Artemisia filifolia and other species in the genus.
--Oxyna aterrima Bud gall (axial or terminal) on terminal branches induced by tephritid fly. See photo G on page 521 of Goeden 2002 article.
--Rhopalomyia Undescribed cotton-wool gall. Partially reviewed but pupal case needed for description and naming. Write A-trid-cottonwool-gall in Observation Field "Linked observation"

Arundo donax--Giant Reed: Tetramesa romana. This biocontrol agent is a wasp that induces galls at the tip of the main shoot and side shoots. A knowledgeable iNat oberver reports that "Some of the largest galls are actually of young main shoots just above the ground."

Atriplex canescens & A. confertifolia--Fourwing Saltbush & Shadscale: Tumor Stem Gall Midge (Asphondylia atriplicis) Relatively large, fleshy integral stem gall. A 2004 Marchosky/Craig study described the gall as a "fleshy, rounded stem-gall near the apical meristem," varying from "small spherical galls to large, slightly irregular, ellipsoid galls" with diameters at the study sites ranging between 4 and 10 mm.

Atriplex canescens--Fourwing Saltbush:
--Asphondylia atriplicicola
--Asphondylia caudicis
--Asphondylia neomexicana According to BugGuide, these are "detachable dense woolly, white, spherical bud galls ... about 1 cm in diameter."

Atriplex polycarpa, A. spinifera, & A. confertifolia—Saltbush & Shadscale: Saltbush Woolly Stem Gall Midge (Asphondylia floccosa) Excellent description at https://bugguide.net/node/view/1452370

Baccharis pilularis--Coyote brush:
-- Baccharis Leaf Blister Mite (Aceria baccharipha) Leaf blister gall
--Coyote Brush Bud Gall Midge (Rhopalomyia californica) Bud gall Also galls B. halimifolia & B. neglecta
-- Coyote Brush Rust (Puccinia evadens) Integral stem gall--orange rust visible through cracks in stem at certain times of year
--Coyote Brush Stem Gall Moth (Gnorimoschema baccharisella) Integral stem gall [common]
-- Rhopalomyia baccharis Curvaceous integral stem gall with elongated diamond-shaped exit holes.

Baccharis sarothroides, B. pilularis, B. salicina—Desert broom and probably Coyote Brush & Willow Baccharis:
--Desert Broom Gallfly (Aciurina thoracica) Integral stem gall 5-17mm long induced by a tephritid fly. See Headrick/Goeden 1993 (gall photos on pg. 75). Article indicates that B. pilularis & B. salicina also serve as hosts. 3 obs of the fly--not the gall--in the SF Bay Area

Baccharis sarothroides—Desert broom:
--Gnorimoschema powelli Spindle-shaped integral stem gall 8x13mm-12x17mm. See also Zobodat site. [1 obs SoCal]
--Rhopalomyia Page 43 of Russo's 2010/2011 Fremontia article shows an undescribed red-purple bud gall ID'd as Rhopalomyia sp.
--Neolasioptera lathami See BugGuide. Soft globular galls near the ends of branches
-- Coyote Brush Rust (Puccinia evadens) Integral stem gall--orange rust visible through cracks in stem at certain times of year. Also reported on B. emoryi and B. thesioides

Baccharis salicifolia--Mule fat: Tephritis baccharis Fusiform (or sometimes subovoidal) bud/integral-stem gall, occurring as "shortened, thickened, succulent terminal parts of main or axillary branches." See Goeden & Headrick (1991) for photocopies of monochrome photos. Occurs only on B. salicifolia. SoCal

Baccharis salicifolia & B. glutinosa--Mule fat and Seep willow: Mule Fat Blister Mite (Aceria baccharices) Irregular bumps on leaves

Berberis dictyota--Shining netvein barberry: Aceria caliberberis. Mite gall. According to Kiefer et al. (page 142-3), "the leaf margin is curled upward, folded, and twisted across the upper surface toward the midrib. The leaf fold may involve the entire length of the leaf margin, with one or two windings forming a tube. The folded leaf eventually becomes crumpled and brown." [0 obs.]

Buxus --Boxes/Boxwood:
-- Box sucker (Psylla buxi) See Ore. State U. site. Psyllid-induced gall in which leaves cup together [common in Sunnyvale & elsewhere]
--Boxwood Leafminer (Monarthropalpus flavus) BTW: Charley Eiseman considers this a gall midge, not a leafminer despite the name, so resist adding it to either leafminer project. Leaf gall [common in Sunnyvale & elsewhere]

Calocedrus--Incense-Cedars: Pacific Coast Pear Rust (Gymnosporangium libocedri) For more info see PNW handbook webpage, USDA page, and Mycoweb page Causes both witches' brooms and orange jelly-like deposits on branches.

Calystegia--False bindweeds: Neolasioptera convolvuli See BugGuide. Integral stem gall [for a leaf gall mite, Aceria malherbae, that is used for biocontrol of Convolvulus arvensis see WSU fact sheet].

Camassia--Camas: Dasineura camassiae More info here Flower bud gall [known only from Pacific NW 0 obs]

Carya--Hickories, including Pecan This genus is not that common in California (although pecan trees are naturalized in some areas). In parts of N. America where it is common it hosts a variety of gall inducers, especially midges. If you do find a hackberry with galls, take a look at this iNat guide to Hickory Midge Galls. If you are still in doubt, ID the gall as "Gall midges," note the host species, and add "@megachile" in a comment, since he made the guide.

Ceanothus sp.--Ceanothus:
-- Ceanothus Bud Gall Midge (Asphondylia ceanothi) In the 2020 world catalog of cecidomyiidae, the host for this is listed as "Ceanothus sp.; C. cuneatus." Round, compact "leafy" bud gall
--Periploca ceanothiella Half-inch long stem swelling. See UC IPM webpage for photos and description

Ceanothus verrucosus--Wart-stemmed Ceanothus: Contarinia sp. Leaf fold gall that eventually turns purplish and forms a purse. Adult midges raised by madily(Madeleine Claire) and ID'd to genus by Ray Gagne. See Madeleine's photo of the gall [San Diego area]

Celtis--Hackberries This genus is not that common in California, but in parts of N. America where it is common it hosts a variety of gall inducers, especially midges and psyllids. We do have 2 observations of the hackberry nipplegall psyllid in California, for example. Best advice if you find a hackberry with galls is to ID the gall as "Gall midges" and note the host species. (You can add "@megachile" if you want, since he is familiar with these galls and is very comfortable with being "@'d.")

Cercocarpus betuloides--Birchleaf mountain-mahogany: Purshivora insignita It appears that Alice Abela has documented the relationship by recording a nymph enclosed in a C. betuloides leaf fold as well as an adult female perched on a "galled" leaf

Cercocarpus parvifolius & possibly C. betuloides--Mountain-mahogany: Dasineura cercocarpi Hairy bud gall; 8-10mm., very tomentose, containing several larvae [Use of this ID for witches brooms is very speculative.] See https://www.jstor.org/stable/25003571?seq=3#metadata_info_tab_contents Felt 1913 p 3/7, p 215

Chamaenerion angustifolium--Fireweed: Mompha sp. This moth causes soft stem galls that often have leaves growing from them. See https://www.inaturalist.org/observations/1815718 for more info.

Chloracantha spinosa--Spiny chloracantha/Spiny aster: Anthonomus ligatus Weevil induces galls [most weevils in galls are inquilines] not sure where gall occurs on plant

Chondrilla juncea--Rush skeletonweed: Aceria chondrillae European mite that forms bud galls on this invasive weed. Described in Plant Parasites of Europe as a "1-1.5 cm coralloid mass of disfigured stems and scale-like leaves" Excellent photo of gall here [1-2 obs in Americas]

Chrysolepis chrysophylla & C. sempervirens--Golden chinquapin and Bush chinquapin: Dryocosmus castanopsidis Round, red gall on catkin/flower

Chrysolepis chrysophylla--Golden chinquapin: Dryocosmus rileypokei This is a wasp that researchers found galling chinquapin NUTS in Plumas County--see https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1063&context=systentomologyusda [no obs] FYI, The golden chinquapin leaf gall appearing as plate 198 in Russo 2006 is now identified as Dryocosmus juliae

Chrysothamnus sp.--Rabbitbrushes: Asteromyia chrysothamni Slightly raised whitish area on leaf or stem

Chrysothamnus viscidiflorus--Yellow rabbitbrush: 5 tephritid fruit flies plus one or more each of moths and midges form bud galls on this host per Goeden/Teerink 1996b.
--Medusa Gall Tephritid (Aciurina ferruginea) Goeden/Teerink 1996 redescribed this gall as "subspheroidal and covered by many thin, threadlike leaves." Adjacent galls can combine to form compound galls. See photo F on p. 432 of article. NOTE: Smooth, non-leafy galls on same host are presumably induced by A. michaeli, as described in this article.
--Aciurina idahoensis Goeden/Teerink 1996b described this gall as a stunted axillary branch (or sometimes branch apex) shaped like a pine cone, and elongating from subspheroidal to ovoid as it matures. Gall bears basally expanded, linearly tapered, apically pointed, smooth-margined leaves, which are shortened and more dense toward the gall apex. Mature galls were ~8-20mm long & 6-12mm wide. Photos on p. 692 of article.
--Rhopalomyia Russo's 2010/2011 Fremontia article mentions his finding "cotton-like terminal flower gall" on this plant and also on rubber rabbitbrush that was identified as a new species of Rhopalomyia [photo on p. 43 of article top left]

Citrus sp.--Citrus, especially lemon Citrus Bud Mite (Aceria sheldoni) Alters the shape of leaves, buds, blossoms, and particularly fruit. Extremely deformed fruit is the best non-microscopic evidence of its presence. (as of spring 2022 all 4 Calif. obs were SFBA)

Convolvulus: See Calystegia

Corethrogyne filaginifolia--California Aster: Asteromyia sp. Flower-shaped bud gall that over time becomes covered with thick white or grayish white cottony webbing. Per Ray Gagne's ID of adults reared by silversea_starsong (James Bailey). See James' comments [10+ obs SoCal]

Cornus florida—Flowering dogwood (non-native): Resseliella clavula Known as the dogwood clubtail midge. Swollen twig; wilted or deformed leaves may also occur. See https://bugguide.net/node/view/614187 https://www.backyardnature.net/galls.htm [no obs]

Corylus avellana—Common hazel: Big bud mite (Phytoptus avellanae) See https://essig.berkeley.edu/documents/cis/cis02_1.pdf [0 obs] [Note that bud galls on native Corylus cornuta are caused by an undescribed midge]

Corymbia --Bloodgums:
--Spotted Gum Lerp Psyllid (Eucalyptolyma maideni) Forms whitish lerps shaped somewhat like fish bones on leaves of Corymbia sp. The lerps are not galls.

Corymbia citriodora--Lemon-Scented Gum:
--Eucalyptus Gall-forming Wasp (Epichrysocharis burwelli) Chalcidoid wasp forms small reddish or brownish blister galls on both sides of leaf [1 obs UCLA]
--Aprostocetus This undescribed species of wasp forms galls that are small, elongate and woody on leaf midribs. See graysquirrel's observation and ID research.

Cotoneaster--Cotoneaster: Plum Bud Gall Mite--see Prunus

Cupressus nootkatensis & C. goveniana pygmaea--Nootka & Pygmy Cypress: Chamaediplosis nootkatensis Photos and info in Duncan 1994 [13 obs]

Cupressus sargentii, etc.--Sargent's Cypress and Pygmy Cypress: Cypress Gall Midge (Walshomyia cupressi)

Cupressuaceae, including Sequoia--Cypress and Redwoods: [NOT A GALL] Cypress Tip Moth (Argyresthia cupressella) Moth that mines tips of cypress and redwood. See UC-IPM and Oregon State IPM. Even though this is a stem-miner, not a gall inducer, it is interesting to look for.

Cuscuta--Dodder: Dodder Gall Weevil (Smicronyx sculpticollis) Gall is typically a broadly fusiform or subglobular enlargement of the peduncle of the flower cluster measuring up to 4-6 mm. However, galls may also be enlarged nodes. See BugGuide [3 obs. SoCal]

Cytisus scoparius--Scottish Broom: Broom gall mite (Aceria genistae) Bud galls of varying size and shape (often diameters of 5 to 30 mm). See Xue et al. article and Pratt et al. article [15 obs N/NW Cal. & SFBA]

Delairea odorata—Cape-ivy: Cape Ivy Gall Fly (Parafreutreta regalis) Spherical gall, about ½" diameter; started in nodes or growing tips, looks like internal stem gall in [cropped] photos; released for biocontrol; See 2017 CA release info and gall photo. More info on p3 and cover.

Dichelostemma capitatum--Blue Dicks: Lasioptera Stem swelling. Tim Frey, who has Gagne's guide, confirmed that this plant is a host of the undescribed Lasioptera stem gall, which Russo reported as occurring on Triteleia laxa

Diplacus aurantiacus--Orange Bush Monkeyflower : Neolasioptera diplaci Stem gall.

Dryopteris arguta--Coastal Woodfern: Fern Leaf Curl Fungus (Taphrina californica) Light yellow-green jelly-like blobs on both sides of leaflets; found May-July

Encelia californica, E. farinosa--[California] Brittlebush: Asphondylia enceliae Felt describes the gall as a "greenish or dark gray, conical, globose, thick-walled gall sometimes confluent and distorting the stem" and also as "a conical, thick-walled, lateral bud gall" 6mm long x 3mm diam., "sometimes twisting the stem." Noticeably hairier than rest of plant. See also Millie's comment

Encelia farinosa--Brittlebush: Rhopalomyia Midge induces a hairy gall on leaves and sometimes petioles or flowers that is taller than it is wide

Ephedra--Mormon Tea: A BugGuide webpage discusses the difference between the two integral stem galls:
--Mormon Tea Stem Gall Midge (Lasioptera ephedrae) Integral stem gall
--Ephedra Stem Gall Midge (Lasioptera ephedricola) Another integral stem gall on several species of ephedra. According to a 1993 paper by Herman et al., The resinous blister galls of Lasioptera ephedricola always have a black ring around them due to association with a sooty fungus, while L. ephedrae galls never do.

Epilobium canum—California fuchsia (zauschneria): California Fuchsia Gall Midge (Contarinia zauschneriae) BugGuide page Bud gall with bud leaves rolled and curled—turns red

Ericameria--Goldenbushes: Asteromyia chrysothamni Slightly raised whitish area on leaf or stem

Ericameria ericoides--California Goldenbush: Gnorimoschema ericameriae Moth forms onion dome-shaped 1 cm. "galls" by sealing terminal leaves together. Described on p. 8 of Powell & Povolny. "Strictly coastal." [0 obs]

Ericameria linearifolia--Narrowleaf goldenbush: Gnorimoschema coquillettella Tip gall B&W photos p. 45

Ericameria nauseosa--Rubber rabbitbrush: Russo lists 8+ species that induce galls on rubber rabbitbrush. These include:
--Gnorimoschema octomaculella [Synonym: G. octomaculellum] Budlike gall composed of terminal leaves. [9 gall obs Sierras and mtns nr LA]
--Rhopalomyia utahensis Felt describes the galls as "Ovoid, hypertrophied leaf buds ... green or somewhat purplish," 10-11mm long with a 7-8mm diam., usually covered externally with "short, recurved, aborted leaflets" covered usually with a thick gray pubescence. Two or three are often confluent.
--Aciurina bigeloviae Cottony white bud galls induced by a fruit fly
--Aciurina trixa Roundish galls attached to the stem. See photo
--Medusa Gall Tephritid (Aciurina ferruginea) See Chrysothamnus viscidiflorus above for more info.

Erigeron spp.--Fleabanes and Horseweeds; plus some “daisies”: Asteromyia modesta More info here Leaf gall--concentric circles on leaf or raised irregular areas; green, purplish, or brown [found on gumplant in San Mateo Cy]

Erodium spp.--Stork's-bills: Synchytrium papillatum (Stork’s bill chytrid) Articles about this fungus refer to the enlarged epidermal cells filled with colored fluid as one-cell “galls” fungus looks like purple-red fish eggs [SoCal&few SFBA]

Eucalyptus--Eucalyptus: Eucalyptus Gall Wasp (Ophelimus maskelli) Reddish bumps on leaves

Eucalyptus--Eucalyptus (particularly blue gum): Eucalyptus Stemgall Wasp (Leptocybe invasa) Yellow-green or red swellings along petiole/midvein galls leaf midrib, petiole, and stem. More info here [57 obs SoCal & SFBA]

Eucalyptus globulus--Tasmanian blue gum: Blue gum gall wasp (Selitrichodes globulus) Galls twigs. Photos here

Eucalyptus--Eucalyptus: Red Gum Lerp Psyllid (Glycaspis brimblecombei) More info here. White sugarloaf structures on leaves.* Eucalyptus camaldulensis, River redgum, is especially susceptible.

Ficus benjamina--Weeping fig: Weeping Fig Thrips (Gynaikothrips uzeli) Non-native insect on non-native plant. Leaf-roll and leaf-fold galls

Ficus microcarpa--Chinese banyan (aka Laurel fig):
--Ficus Gall Wasp (Josephiella microcarpae) Leaf blister gall. Info and/or photos here. [SoCal]
--Ficus Leaf-rolling Psyllid (Trioza brevigenae) Feeding causes very tight leaf rolls. Best to look for larvae inside roll gall as other species create looser leaf rolls on this plant. See BugGuide page [SoCal]

Ficus microcarpa, F. retusa--Cuban laurel etc.: Cuban Laurel Thrips (Gynaikothrips ficorum) Can cause rolling, pitting, and discoloration of leaf. See USDA Pest Thrips Field Guide Ficus microcarpa is preferred, but F. retusa, viburnum, and citrus are also hosts.

Frangula californica & F. rubra--Coffeeberry and Sierra coffeeberry: Midrib Gall Moth (Sorhagenia nimbosus) leaf folding in half lengthwise

Frangula californica--Coffeeberry: Dasineura sp. See page 58 of Pepperwood Preserve Vascular Flora, "The flowers are galled by an undescribed gnat of the genus Dasineura that causes the flowers to inflate in a way that mimics the green fruits."*** And see photo. Flower gall

Fraxinus sp.--Ash: Prociphilus fraxinifolii "Ash leafcurl aphid"--see photos on UC IPM page and also look for white waxy secretions and aphids without distinct cornicles. Caution: Other Prociphilus species also curl ash leaves in California, so ID to genus level may be preferable.

Fuchsia spp.--Fuchsia [not California “fuchsia”]: Fuchsia gall mite (Aculops fuchsiae) More info here. Thickens and distorts leaves and shoots

Galium angustifolium--Narrow-leaved Bedstraw: Resseliella ID'd to genus by Ray Gagne from larvae reared by silversea_starsong

Garrya sp.—Silk tassel: Asphondylia garryae Catkin and bud galls. See comments here.

Genista monspessulana--French broom: Aceria davidmansoni Gall inducer previously believed to be Aceria genistae (which does occur in Calif. on Scottish broom).However, Han et al. examined mites collected from French broom in Daly City and determined that the mites were A. davidmansoni.

Gleditsia triacanthos—Honeylocust: Gleditsia Gall Midge (Dasineura gleditchiae) More info here. Leaflet tip swelling [3 obs SFBA]

Glechoma hederacea--Ground-Ivy: Glechoma Gall Wasp (Liposthenes glechomae) Non-native wasp galling non-native plant in Eastern U.S. and Eurasia--possible for California, where plant also occurs. According to Taylor, galls usually occur on leaf or petiole, but stem, flower, and apical galls are possible. Smaller galls are round, green (turning reddish) and hairy and typically 6-10mm in diameter. Compound galls are more variable in shape and can be 18mm long. See also BugGuide. [0 CA obs]

Grindelia sp.--Gumplants:
--Asteromyia modesta More info here. Leaf gall (circles on leaf or raised irregular area on leaf; green, purplish, or brown) [5 obs]
--Asteromyia grindeliae Described by Felt as a "greenish or blackish oval, blister leaf gall" 3-4mm diameter and found by him on Grindelia hirsutula and G. robusta.

Grindelia hirsutula—Hairy gumweed:
--Gnorimoschema grindeliae Soft stem (node) gall turns white with purple-brown by May—BW photos here. on p45. [3 obs SF East Bay]
--Rhopalomyia grindeliae: Monothalamous (single-chambered) gall on flowerhead; only 5mm long unless they agglomerate [3 obs]
--Cecidomyiidae: Undescribed multi-chambered leafy bud gall shown in plate 234 of Russo that can grow to 8x the size of R. grindeliae

Gutierrezia sp.—Matchweeds and snakeweeds:
--Matchweed Stem Gout (Asteromyia gutierreziae) Felt describes the galls as "irregular, dull black thickenings" 6-8mm long that double the flower stems' thickness to 0.5mm. [19 obs SoCal]
--Epiblema rudei J. Powell article in Fremontia; see photo bot.rt. pg 9. Woody stem gall [3 gall obs]

Hedera helix—English ivy: Phytoptus hedericola Info here on pg 9. Galls in buds and at petiole bases cause deformation and stunting [no obs. May not be a true gall]

Helianthus annus--Common Sunflower: Bucculatrix longula Moth that reportedly causes a stem gall [0 obs]

Heteromeles arbutifolia--Toyon: Toyon Gall Thrips (Liothrips ilex) Leaf blistering, curling, and distortion. Info and/or photos here and here. FYI: Leaf puckering and twisting on toyon can also be caused by the fungal disease, scab, according to a UC-IPM post. See also this other reference to scab on toyon

Holodiscus discolor--Ocean spray:
--Dasineura sp. Swollen leaf vein fold
--Colomerus holodisci Erineum mite causing erineum galls on leaves [possibly colorful]. Most iNat obs from BC (1 WA) but holotype was in Calif.

Hypochaeris spp.--Cat's-Ears: Catsear Gall Wasp (Phanacis hypochoeridis) Integral stem gall

Isocoma--Jimmyweeds and Goldenbushes: [for those species previously in Haplopappus] Asteromyia chrysothamni Slightly raised whitish area on leaf or stem

Isocoma acradenia--Alkali Goldenbush: Procecidochares blanci Tephritid bud gall with up to 20 rows of scale-like leaves. See photo F in Goeden & Norrbom 2001 [2 CA obs+1 NV]

Isocoma menziesii--Coastal goldenbush: Gnorimoschema crypticum Info and/or photos here. “[F]leshy stem gall . . . galls . . . are soft, variable in form, and ephemeral, similar to [G. grindeliae].” [no obs]

Juglans californica & J. hindsii--Southern California walnut and Northern Calif. Black Walnut:
-- California Black Walnut Pouch Gall Mite (Aceria brachytarsa) leaflet gall consisting of bumpy sometimes reddish pouches raised about the upper leaflet surface on short stalks
--Black Walnut Petiole Gall Mite (Aceria caulis) petiole gall of thick pinkish, purplish, or brown erineum
-- Aceria neobeevori . Catkin gall [2 SoCal obs]

Juglans regia--Persian Walnut: Walnut Blister-Mite (Aceria erinea) Leaf blisters

Juncus--Rushes: Livia Several species in this psyllid genus gall the inflorescence of rushes. The galls and psyllids are much more common in other parts of the US, but iNat does have 3 California sightings of the tiny psyllids. Try to get several photos of the plant to ID it to species, and if possible, a psyllid photo as well.

Juniperus californicus & J. occidentalis—California juniper and Western Juniper: Juniper Urn Gall Midge (Walshomyia juniperina) Joyce Gross's photos.

Juniperus californicus & possibly others—California Juniper: Walshomyia sp. Joyce Gross's photos.

Larrea tridentata--Creosote Bush: 15 described species of Asphondylia and an undescribed Contarinia species induce galls on Creosote bush in the desert SW. Helpful online resources include: a 1990 Gagne & Waring article with tiny drawings of all 15; photos by Joyce Gross here and here; and an iNat Creosote gall project.
--Creosote Gall Midge (Asphondylia auripila) Round bud gall composed of densely packed narrow [?]bracts.
--Leafy Bud Gall Midge (Asphondylia foliosa)
-- Creosote Antler Gall Midge( Asphondylia digitata)
--Creosote Cone Gall Midge (Asphondylia rosetta)
--Asphondylia pila This is Russo's "Leaf Club Gall Midge" in plate 218. Per Russo's updates to his guide, the name has been changed from A. pilosa to A. pila.
--Creosote Resin Gall Midge (Asphondylia resinosa)
--Creosote Bush Flower Gall Midge (Asphondylia florea)
--Asphondylia apicata
--Creosote Bush Club Gall Midge (Asphondylia clavata)
--Asphondylia discalis
--Asphondylia fabalis See Tim O'Connor's comments to this observation for his description of the gall.
--Asphondylia barbata See Tim O'Connor's comments to this observation for his description of the gall.

Laurus nobilis--Bay laurel (non-native): Bay sucker (Lauritrioza alacris). Psyllid causing distorted terminals, galled leaves, and stunted plant growth. See Bladmineers photos. This non-native psyllid has been confirmed in N. America in California and NJ.

Lepidospartum squamatum--California broomsage:
--Scalebroom Bud Mite (Eriophyes lepidosparti) Bud gall [5 obs. SoCal]
--Scrobipalpopsis sp.; Moth stem gall mentioned on p. 54 of Russo's guide

Lavatera. See Malva.

Lonicera hispidula—Pink honeysuckle: Lonicerae russoi [NEW SPECIES—was Rhopalomyia sp. B--Russo plate 238] More info here and photo Green, leafy rosette bud gall

Lonicera subspicata--Southern Honeysuckle: Lonicerae lonicera Midge-induced bud gall (formerly Honeysuckle Gall Midge (Rhopalomyia lonicera)) [Russo's guide also illustrates an undescribed bud gall for this species.]

Lupinus arboreus--Coastal bush lupine and possibly other species
--Dasineura lupini Large hairy, irregular bud gall
--Lupine Stem Gall Midge (Neolasioptera lupini) Stem swelling

Lupinus arboreus, varicolor, albifrons, albicaulis & chamissonis—Coastal bush lupine et al.: Lupine Leaf Gall Midge (Dasineura lupinorum) See Gagne 1993 Leaflet gall that develops while leaflet is still folded and elongating; leaflet remains folded above larva/e--galls that turn reddish are likely to have dead larvae.

Lycium cooperi--Peach-Thorn:
--Symmetrischema sp. Stem gall shown in Plate 182 of Russo (2006) [Plates 381-2 of Russo 2021] is induced by a moth in this genus. Will look for species name when pending paper is published. ID to "Gnorimoschema" no longer correct
--Contarinia sp. Described as "cabbage-like bud galls" in Russo's 2010/2011 Fremontia article. See photo at bottom left of pg. 43 of article.

Malva assurgentiflora--Island Mallow: Island mallow psyllid (Bactericera lavaterae) See https://bugguide.net/node/view/1353857. Leaf blister

Microseris sp.--Silverpuffs: Microseris Stem Gall Wasp (Antistrophus microseris) Stem swelling [3-4 obs]

Myoporum sp.--Ngaio: Naio Thrips (Klambothrips myopori) More info here Look for severe leaf distortion

Notholithocarpus densiflorus--Tanoak:
--Live Oak Witches' Broom Fungus (Cystotheca lanestris) A powdery mildew that causes witches' brooms and/or whitening on new branches of tanoak, as well as several oaks
--Tanoak Gall Wasp ( Andricus notholithocarpi) Nicholls et al. 2018 Forms small bud-shaped galls on catkins, buds, and leaf edges. Galls are ribbed lengthwise (i.e., going toward the narrow tip) and vary from pale green when fresh to rust brown. Leaf edge galls induce folds. In addition, a 4th variant causes swelling and some bending of leaf midrib. Look for a tiny "bud" with vertical fissures; a tiny cone at the edge of a leaf underside that may pull the leafedge closer to the midrib, or a tiny yellowish torpedo with fissures/ridges poking out from a catkin. [found in Humboldt and possibly San Mateo cys] [1 confirmed obs near Mount Tam in Marin!!!]
--Tanoak often displays a thick growth of yellowish erineum not too different from the Aceria mackiei gall, but much longer and thicker and on both sides of the leaf. Although A. mackiei cannot be completely ruled out, most believe this is an undescribed Eriophid mite gall.

Opuntia--Prickly pears: Asphondylia betheli See BugGuide page. Swollen fruit gall, sometimes with cylindrical exuvia poking sideways out of it. [0 Calif. obs]

Parkinsonia florida--Blue Palo Verde: New research seems to indicate that Palo Verde witches' broom is caused by an emaravirus that is probably transmitted by the gall mite Aculus cercidi.

Picea--Spruces:
--Douglas Fir Adelgid (Adelges cooleyi) This aphid relative, also known as the Cooley spruce adelgid, galls the tips of spruce branches. See Forest Pests brochure pp. 53-5 and Influential points website for info and photos.
--Spruce Witch's Broom Rust (Chrysomyxa arctostaphyli) See Forest Service webpage. Witches' broom. Infected leaves turn yellow, produce spores, and drop off. [3 obs]

Pinus--Pines:
--Western Gall Rust (Cronartium harknessii) Integral stem gall, but fungus can sometimes also produce grapefruit-sized galls on trunks
-- Elytroderma deformans Fungal disease that causes large witches' brooms and needle cast in Ponderosa pine and several other species of pines. In 2019 it caused "severe witches’ brooming" in Ponderosa pine along a 2-mile stretch of the west shore of Lake Almanor. See USFS document and USFS guide for AZ & NM

--Podapion gallicola Spindle-shaped stem gall; adult weevil chews a niche in the bark of a one-year-old twig. See ForestPests webpage. Only iNat sighting of weevil occurred in Ontario, but BugGuide confirms it ranges into California. [0 obs]

Pinus radiata--Monterey Pine: Thecodiplosis piniradiatae Needles swollen at base (usually all 3 needles in the sheath) and ~ 1/3 normal length [1 obs]

Poaceae--Grasses
--Danthonia californica (California Oatgrass): Cynipanguina danthoniae Green globular nematode galls on grass blade. See U.C. Davis notes. 14 obs., mostly SF N.Bay

Polystichum munitum--Western sword fern: Taphrina faulliana. Round or oval lemon-yellow spot on frond with slightly thickened tissue. Leaf may curl, possibly looking blistered, and spot turns dark with grayish asci on top. Recorded from Muir Woods and Aptos in 1950s. Also occurs in Oregon and BC.

Populus sp.--Poplars, Cottonwoods, and Aspens:
--Poplar Twiggall Fly (Euhexomyza schineri) See Montana field notes and page 83 of USDA aspen guide Integral stem gall on twigs of various Populus species
--Phyllocolpa sawflies roll or fold the edges of Salaceae leaves, including Populus species, sometimes forming galls or pseudogalls.
--Poplar Leaf-base Gall (Pemphigus populicaulis) Roughly globular gall composed mainly of petiole tissue that starts on the leaf blade and incorporates some of the leaf blade, twisting the petiole. See description on pg. 289 of Floate (2010) and photo 9 on page 287. See also BugGuide.

Populus fremonti—Fremont cottonwood: Pemphigus obesinymphae Globular swelling of petiole (leaf "stem") near leaf blade with transverse slit. Before Aoki and Moran described it in 1994, P. obesinymphae galls and aphids were believed to be a variant of P. populitransversus galls and aphids. Subsequently, a 2004 paper by Abbot & Withgott established, based on DNA analysis, that the galls in the SW U.S. on Populus fremonti, which has been thought to be P. populitransversus, were instead induced by the closely related Pemphigus obesinymphae aphids. Characteristics that separate P. obesinymphae galls from P. populitransversus galls are: gall is close to leaf blade; gall occurs on late-flushing leaves rather than appearing in spring; gall is globular rather than elongated; a 1.2 mm ostiole occurs along the slit. The 2004 paper seems to say that Fremont cottonwood is not a host for P. populitransversus. FYI, the 2004 paper was unearthed by megachile. It not only slipped by Russo's and my radar, but its findings are not as of 2/17/2022 mentioned on the superb aphidsonworldsplants website.

Populus fremonti, P. tremuloides, P. trichocarpa--Fremont cottonwood, Trembling aspen, Black cottonwood: Aceria parapopuli Galls on buds/catkins [16 obs all E of Sierra crest]

Populus fremonti, P. deltoides--Fremont cottonwood, Eastern cottonwood: Pemphigus obesinymphae. Leaf petiole gall very similar to Pemphigus populitransversus. Key difference in gall is the presence of an ostiole on the slit. The ostiole is circular and measures ~ 1.2 mm diameter on an 8-16 mm diam. gall. Gall position tends to be closer to leaf blade than P. populitransversus galls. Galls form on late-flushing leaves and aphids remain in gall until late autumn. Present in UT, AZ, OH, TX, TN and may be present in CA. See Aphids on the World's Plants for description. See Aoki & Moran (1994) for more info.

Populus fremonti, P. angustifolia, P. trichocarpa—Fremont cottonwood, Narrowleaf cottonwood, Black cottonwood: Pemphigus populivenae Leaf fold galls but also, according to Russo, pouchlike galls on midrib or along leaf edges

Prunus--Plums, cherries, and allies [stone-fruit; also almonds, cotoneaster]: Almond and Plum Bud Gall Mite (Acalitus phloeocoptes) http://mgsantaclara.ucanr.edu/files/300211.pdf https://bugguide.net/node/view/1643676 first found in Morgan Hill, CA 2/2019 and at UCSC 1/2020 Enlarged bud scales (diameter ~ 1.5mm) surround buds [0 obs]

Prunus—Peach, Nectarine, and other stone fruits: Peach Leaf Curl (Taphrina deformans)

Prunus andersonii—Desert peach: Eriophyes (?) prunandersonii https://essig.berkeley.edu/documents/cis/cis02_1.pdf pg 7-8 baggy erineum deformation on leaves [no obs]

Prunus ilicifolia--Hollyleaf cherry Taphrina thomasii. Fungus causes witches' brooms. See Mix 1949 p. 142.

Prunus subcordata--Pacific plum: Pocket plum (Taphrina pruni or T. pruni-subcordatae) See https://www.jstor.org/stable/2436510. T. pruni causes fruit-pockets on various Prunus species, including Pacific/Sierra plum; T. pruni-subcordatae, which may be a distinct species, causes witches' brooms on Pacific/Sierra plum. The latter is mentioned in Russo's Table 7. See NatureNiche for a description of finding the plum pockets on Modoc Forest Rd. in Shasta County [0 obs]

Prunus virginiana and other prunus--Chokecherry and other prunus:
--Plum Finger Gall Mite (Eriophyes emarginatae) Narrow finger-like pouches on upper leaf surface [17 obs]
--Taphrina confusa Fungus can cause what Russo 2006 describes as "massive" witches' brooms on western chokecherry and Sierra plum. Mix 1949 describes it as deforming fruits and flowers of P. virginiana and P. alabamensis.

Pseudognaphalium luteoalbum, etc.--Jersey cudweed, other rabbit-tobaccos, etc. Trupanea signata Woolly terminal bud gall and integral stem gall. Native fruit fly on non-native hosts causes elongate-obclavoidal expansion of pith parenchyma of auxilliary branches and stems. Larvae feed in an open cavity of this woolly-covered gall. Flowers and branches may grow from gall. See Goeden/Teerink 1997, esp. photos and description of gall p. 753. Species occurs in much of Western U.S. on species of Gnaphalium, Pseudognaphalium and Anaphalis.[0 obs]

Pseudoziziphus parryi--California Crucillo: California Crucillo Gall Mite (Aceria neocondaliae) Small blister galls on leaves [1 obs SoCal]

Pyrus communis, P. malus—Pear and Apple: Pear Leaf Blister Mite (Eriophyes pyri) See https://essig.berkeley.edu/documents/cis/cis02_1.pdf and https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1897&context=extension_curall Leaf blisters may be shallow and reddish or brownish [1 obs Santa Cruz]

Quercus sp.--Oaks:
--Stegophylla A woolly aphid, Stegophylla essigi, known only from the West Coast, creates leaf fold galls on "many California oaks, including blue, valley, Oregon white, coast live, interior live, California black, and scrub oak." The leaf margins--at least those on Coast live oak--are folded upward and become reddish. See USDA California oak guide pages 46-7 [it's now download-only]. However, Merav has commented that several aphids make leaf roll/fold galls on California oaks. So it's probably best to ID to genus level. To further complicate matters, Merav mentioned that Joyce Gross has found Cecidomyiidae larvae in Quercus agrifolia leaf folds--these midge galls may be Macrodiplosis erubescens, which does cause leaf folds elsewhere in the US--see BugGuide page Leaf fold gall
--Live Oak Witches' Broom Fungus (Cystotheca lanestris) A powdery mildew that causes witches' brooms and/or whitening on new branches of Coast live, Canyon live, and Valley Oaks, in addition to tanoak.

Quercus chrysolepis--Canyon live oak: Heteroecus malus Joyce Gross's photos. Non-integral stem gall (usually found in clusters)

Quercus douglasii—Blue oak: Aceria trichophila https://joycegross.com/images.php?taxon=Aceria+trichophila&ordr=. Leaf pouch gall [1-2 obs]

Quercus dumosa, Q. garryana, Q. engelmanni (oak): Andricus bakkeri [="Pinched Leaf Gall Wasp." in Russo’s guide] See https://www.biodiversitylibrary.org/item/255100#page/306/mode/1up page 292 and https://bugguide.net/node/view/1016350. Leaf gall [11 obs]

Quercus cornelius-mulleri--Muller's oak: Russo's "Brown eye gall wasp" [plate 132] that galls the underside of Muller's oak leaves along the midrib has been identified as as species of Dryocosmus

Quercus palmeri--Palmer’s oak:
--Heteroecus fragilis More info here. Stem gall—spongy
--Lyon’s gall wasp (Heteroecus lyoni) detailed drawings in a 1924 article More info here. Photo on pg. 45 of Russo's Fremontia article. Leaf gall shaped like planter/urn [0 obs]
--Loxaulus boharti Dailey/Sprenger 1983. says the wasp induces an integral stem gall: 0.5mm holes in 2 mm circles and slight bark swelling**** [holotype from CCosta Cy.; paratypes Riv. Cy.]
--Andricus burnetti More info here. Photo on pg. 45 of Russo's Fremontia article. Bud or petiole gall

Quercus suber—Cork oak: Plagiotrochus suberi/amenti [non native gall on non native cork oak] tiny photos of gall http://www.iresa.agrinet.tn/tjpp/7BenJamaa1.pdf p2 [0 obs.]

Quercus vacciniifolia--Huckleberry oak: Dasineura sp. Russo has determined that the "Purse gall midge" in Plate 151 is a species of Dasineura

Rhamnus crocea & R. ilicifolia--Redberry Buckthorn & Hollyleaf Redberry: undescribed flower gall identified to genus by Ray Gagne. Schizomyia. See photos

Rhododendron—Azalea specifically: Cowberry Redleaf (Exobasidium vaccinii) See https://pnwhandbooks.org/plantdisease/host-disease/azalea-rhododendron-spp-leaf-flower-gall http://plantclinic.cornell.edu/factsheets/azaleagall.pdf. Strangely shaped leaf galls and witches brooms

Rhus integrifolia; R. trilobata--Lemonade berry & Rhus trilobata: Asphondylia integrifoliae
This midge causes "swollen, aborted flower buds"

Ribes--Currants:
--Ribesia sp. See https://bugguide.net/node/view/1474423. Leaf gall induced by midge; forms round purplish blisters on leaves
--Potato Aphid (Macrosiphum euphorbiae) Leaf rolls that can go all the way to the midrib. Look for pale green.
--Rhopaolmyia Undescribed flower-like bud gall; Russo 2006 plate 231
--Redcurrant Blister Aphid (Cryptomyzus ribis) Red-purple hyperplasia blisters on leaves of Ribes sp. This is a European aphid that migrated to N. America. Presence in Calif. unconfirmed. See Plant Parasites of Europe and Mike's Garden for photos. An ag.umass.edu webpage says the aphids cause the leaves " to curl downward, blister, and become reddish. In severe cases, leaves become excessively distorted and fall off..."

Ribes roezlii & Ribes divaricatum--Sierra gooseberry & Spreading gooseberry: Currant Leaf Gall Mite (Eriophyes breakeyi) Pouchlike leaf galls covered with noticeable white hairs that join over the lateral veins and midrib to form what Kiefer et al. describes as "globular chambers" in An Illustrated Guide to Plant Abnormalities Caused by Eriophyid Mites in North America--photos on p 69. [0 obs]

Robinia pseudoacacia --Black locust: Locust Gall Midge (Obolodiplosis robiniae) See photos Leaf roll gall [2 Calif. obs--L.A.]

Rubus--Blackberry: Redberry mite (Acalitus essigi) fruit discoloration gall. Keifer: “Infested berries show swollen, brilliant red or pink and greenish drupelets among unaffected purple or maroon drupelets. Some berries have entirely red drupelets. Affected berries remain red or green and do not ripen normally.” https://naldc.nal.usda.gov/download/CAT87208955/PDF pg 126 [0 obs]

Rubus parviflorus—Thimbleberry:
--Diastrophus kincaidii See Wangberg 1975. Lumpy, irregular integral stem gall
--Illinoia sp. Russo 2021 has a leaf roll gall identified as Masonaphis sp. It looks like that is a subgenus of Illinoia.

Salix—Willow: [To ID common Calif. willows see this key.]
--Willow Bead Gall Mite (Aculus tetanothrix)
--Willow Apple Gall Sawfly (Euura californica) Leaf gall--one of many bright red roundish sawfly galls on willow. Look for tiny "tubercules" interrupting the smooth surface.
--Willow Bean Gall Sawfly (Euura proxima) Bean shaped, bright red leaf gall
--Aculops aenigma Believed to cause catkin and bud galls [3 obs E of Sierras & SF East Bay]
--Willow Pinecone Gall Midge (Rabdophaga strobiloides) Pine cone shaped apical bud gall
--Willow Rosette Gall Midge (Rabdophaga salicisbrassicoides) There are several rosette galls on willow, and the taxonomy appears to be very confused.**
--Willow Beaked-gall Midge (Rabdophaga rigidae) See BugGuide 1 & 2& Joyce Gross's photos.
-- Potato Gall Midge (Rabdophaga salicisbatatus) large [up to 2cmx4cm] integral stem gall
--Euura sp. Willow sawfly galls that are truly on the petiole rather than at the leaf base are the work of Euura sawflies, according to S.K. Monckton, an iNat curator who studies sawfly systematics. For the present, leaf base galls can be attributed to Pontania sp. [FYI, the petiole is the stalk that attaches the leaf blade to a twig]
--Phyllocolpa sawflies roll or fold the edges of willow leaves, sometimes forming galls or pseudogalls. See BugGuide webpage.

Salix laevigata, amygdaloides, hookeriana, matsudana, & nigra--Willow: Western Red Willow [Gall] Mite (Aculus laevigatae) Beadlike leaf galls with lower surface openings. See megachile's comment here
Salix lasiolepis--Arroyo Willow: Arroyo Willow Stem Sawfly (Euura lasiolepis) stem gall

Salix exigua--Narrowleaf Willow: Willow Stem Sawfly (Euura exiguae)

Salix gooddingii--Goodding's willow: Aculus vallis mite bead gall on leaf; per comment by megachile, presumably based on unpublished Amrine catalog

Salvia mellifera & S. apiana--Black sage and White sage:
-- White Sage Leaf Gall Midge (Rhopalomyia audibertiae) Tubular galls, 8mm x 12 mm, on leaf or petiole, with a shallow protrusion on the opposite side of the leaf from each tube and an opening/depression at the end of each tube. See photos at Natural History of Orange Co.
--Rhopalomyia salviae produces smaller [2mm x 5 mm] tubular galls on leaf or, more commonly, stem that are straight-sided and are ordinarily at right angles to the stem.

Sambucus cerulea & S. canadensis—Elderberry: Elderberry Gall Midge (Schizomyia umbellicola) Florets expand to form vase-like galls

Schinus molle--Peruvian peppertree: Peppertree psyllid (Calophya schini) [U.S. psyllid had been mis-identified as Calophya rubra] Pit galls on leaves [also on petioles, twiglets, and flower buds]

Senegalia greggii--Catclaw acacia: Tanaostigmodes howardii Krombein's 1979 Hymenoptera catalog says this wasp "produces small, spherical bud galls on Acacia [Senegalia] greggi, Mimosa biuncifera, Prosopis sp." Russo 2006 attributes an integral stem gall to this wasp [Plate 186], and his "errata" webpage adds that the gall in Plate 17, which looks like a group of spiny pinecones, is also attributable to T. howardii. [Note that BugGuide shows an unidentified gall very similar to the Plate 17 gall with the caption "Gall midges emerging..."]

Solidago sp.--Goldenrods: Asteromyia modesta More info here. Leaf gall (concentric circles on leaf or raised irregular area on leaf; green, purplish, or brown)

Symphoricarpos albus & S. mollis-- Common snowberry and Creeping snowberry:
--Snowberry sawfly (Blennogeneris spissipes) Lumpy, whitish bud gall
--Phyllocoptes triacis Slender leaf roll gall induced by a mite
--Dasineura sp. Slightly thicker leaf roll gall caused by a midge Gall was originally mis-attributed to Reseliella californica; ID remained Dasineura sp. as of 5/2020
--Chiosperma turgidum https://zenodo.org/record/263700#.XzyIAMhKjtQ elongate bud gall 5mmx8-10mm [Wash. holotype—may not be in Calif. Use only if Blennogeneris spissipes doesn’t fit]

Symphyotrichum chilensis—Pacific aster: Gnorimoschema subterranea BW photos in Powell & Povolny article on p45. Large, nearly spherical to watermelon-shaped stem galls (17-27mm long, 12-16mm diameter) soft, becoming woody; some 12-15 cm or more above ground level, with others a mere 2-5cm above roots. Charley Eiseman notes that Gnorimoschema exit holes are typically plugged with frass. [1 obs. reported from SFBA]

Syzygium--Brush Cherry and Lilly Pilly: Syzygium Leaf Psyllid (Trioza adventicia) [formerly misidentified as T. eugeniae] Leaf pit galls

Tetradymia axillaris, T. glabrata, & T. stenolepis--Horsebrushes and cottonthorns: Scrobipalpopsis tetradymiella Integral stem gall covered in white woolly fibers—[1 obs SoCal]

Tipuana tipu --Pride of Brazil: Tipu Psyllid (Platycorypha nigrivirga) Photos and info, see UC Riverside webpage. Causes leaf curl that may possibly be severe enough to count as a gall plus waxlike pellets.

Toxicodendron diversilobum--Pacific Poison Oak: Poison Ivy Leaf Mite (Aculops rhois) [Synonym: Aculops toxicophagus]

Trichostema--Bluecurls: Stagmatophora enchrysa Moth stem gall; no details [no obs yet]

Trifolium--Clover: Clover Leaf Midge (Dasineura trifolii) Photos and info at Bladmineerders website European gall that has been found in N. America since 19th century. BugGuide has sightings from New England, status in Western US unknown. Leaf fold gall [0 obs]

Triteleia laxa--Ithuriel's spear: Lasioptera Integral stem gall

Ulex europaeus--Gorse: Aceria davidmansoni Gall inducer previously believed to be Aceria genistae (which does occur in Calif. on Scottish broom).However, Han et al. examined mites collected from gorse in Daly City and Albany in California and from Washington state and determined that the mites were A. davidmansoni.

Urticae--Nettles Nettle Clustercup Rust Fungus (Puccinia urticata) The aecia can cause large leaf blisters as shown in these photos

Vaccinium--Blueberries, cranberries, and allies: Azalea Gall (formerly cowberry redleaf) (Exobasidium vaccinii) [Note that Exobasidium maculosum, which has made headlines, galls Vaccinium species in the SW U.S--not in California.]

Vaccinium ovatum--Evergreen huckleberry: Huckleberry Broom Rust Fungus (Calyptospora columnaris) Photos and info, see PNW handbook. Affects various Vaccinium species and fir, but causes swollen (often leafless) stems and witches' brooms on V. ovatum.

Viola--Violet: Prodiplosis violicola Midge-induced leaf roll gall affecting several species of violets, native and not. See BugGuide. Rolls one or both leaf edges up. [4 obs in SFBA 3/2021]

Vitis sp.—Grapes:
--Grape Erineum Mite (Colomerus vitis) Red or green leaf blisters with white-to-fuchsia erineum pockets on underside
--Grape Phylloxera (Daktulosphaira vitifoliae) Induces what Aphids on the World's Plants describes as "hairy, scabrous galls" on leaf underside with openings on the upper leaf surface. Also galls roots. Susceptibility, presence and number of leaf and/or root galls, and other factors depend on which species of Vitis is involved and climate. Galls are much more common in NE and N. Central states of the US than they are further south, but the leaf galls do occur in California to some extent on native and hybrid grapes.

Wyethia—Mule ears: Anguina balsamophila This nematode induces leaf blisters on Wyethia in the Sierras and on
Balsamorhiza (Balsam root), as well as galling common sunflower (Helianthus annuus) in Europe . See U.C. Davis notes. 1 obs.

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• Not a true gall. A true gall is a growth of the plant itself in response to a stimulus from another organism. Many of the mistletoes and rusts in the Galls of California also are not true galls, although at least some mistletoe and rust species can sometimes cause galling.

** More on willow rosette galls:
--An Alaska study of willow rosette galls had some interesting findings. http://www.akentsoc.org/doc/AKES_newsletter_2018_n1_a03.pdf
--Russo 2021 includes only Rabdophaga strobiloides (which is pine-cone-shaped), R. salicisbrassicoides [also recorded in Iowa and Mich], and an undescribed cone-shaped rosette-like Rabdophaga bud gall made up of strongly recurved thick, inflexible bracts that occurs on arroyo willow and related species. But he mentions that the taxonomy of willow galls generally is challenging, with a lot of work to be done.
--R. rosaria species complex is not confirmed for North America. per https://bugguide.net/node/view/357587#633028 yet we have >100 iNat obs in the U.S. [https://www.inaturalist.org/observations?verifiable=true&taxon_id=494431&place_id=&preferred_place_id=1&locale=en] and Canada.
--For Raymond Gagne's couplet and some info, see https://bugguide.net/node/view/854099/bgpage
--A 2/2020 article looking at R. rosaria and some R. brassicoides in Eurasia and Alaska proposes subdividing them into many species based on clades. [https://academic.oup.com/zoolinnean/article-abstract/doi/10.1093/zoolinnean/zlz179/5741357?redirectedFrom=fulltext]
--For a story illustrating the difficulties of IDing the cause of willow stem swellings, read this entry in Charley Eiseman's blog.

*** Dasineura sp. ID based on Raymond Gagne's ID of samples author Greg de Nevers sent to him.
**** In their 2000 article at https://www.biodiversitylibrary.org/page/16185855#page/204/mode/1up, Melika and Abrahamson apparently erroneously describe Loxaulus boharti galls as "yellow, pubescent aborted axillary bud or leaf petiole galls." The same paragraph "Biology," also states a different emergence time than Dailey/Sprenger for the only generation known, but does end with the attribution "(Dailey and Sprenger 1983)."

Search for observations with A. tridentata listed in obs field "Host"; "Host plant":
https://www.inaturalist.org/observations?place_id=14&field:Host=75598
https://www.inaturalist.org/observations?place_id=14&field:Host%20plant=75598
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