Hairy Matilija Poppy (Romneya trichocalyx)
https://www.inaturalist.org/observations/6573028 by @johnmartin

Coulter's Matilija Poppy (Romneya coulteri)
https://www.inaturalist.org/observations/42735058 by @finatic

The flowers of Matilija poppies are so spectacular that it is easy to overlook other defining characteristics of the two species, Hairy Matilija Poppy (Romneya trichocalyx) and Coulter’s Matilija Poppy (R. coulteri), both of which are found in San Diego County. If present, unopened flower buds are most helpful in separating the two species. The sepals of R. coulteri are without hairs, while the sepals of R. trichocalyx are hairy as seen in our observations of the month. Usually, the sepals of R. coulteri form a distinct beak at the top of the bud; R. trichocalyx has no beaking or only indistinct beaking.

R. trichocalyx with bud showing hairy sepals and no beaking. (c) John Martin. CC by-NC

R. coulteri with buds showing sepals without hairs but with beaking. (c) BJ Stacey.

Unfortunately, the sepals fall off shortly after the flowers open. The peduncle (flower stem) of R. trichocalyx may be bristly at the top; the peduncle of R. coulteri has no hairs. The flowers, leaves, and fruits of R. trichocalyx may be smaller than the flowers, leaves, and fruits of R. coulteri, but there is much overlap, so measurements of these structures won’t hurt, but often they will not be helpful. Although the fruits appear distinctive, both species have similar hairy fruits. If seeds are present, R. coulteri will have bumpy, dark brown seeds, while the seeds of R. trichocalyx are smooth and usually lighter brown.

When R. coulteri was first described in 1845, it was the only species in the genus. In Asa Gray’s 1878 Synoptical Flora of North America, its distributional range was described as extending from Ventura County (home of Matilija Canyon) south to Baja California. In 1898, Alice Eastwood described Romneya coulteri var. trichocalyx which is currently a separate species (R. trichocalyx) on the Jepson eFlora, the Checklist of Vascular Plants of San Diego County (4th Ed.) and other authorities. The distributional range of naturally occurring R. coulteri is more limited than that of R. trichocalyx. Until widespread introduction of R. coulteri, both were found from Ventura County south to just a short distance into San Diego County, but only R. trichocalyx was expected in the rest of San Diego County and in Baja California. Matilija poppies have been wildly popular with gardeners for many years. R. coulteri (or a cultivar, possibly a hybrid of the two species) has been planted in many places throughout San Diego County. Plants readily spread through their underground rhizomes.

All this makes it important when posting observations to iNaturalist that you include more than just a photo of the flower to identify which species of Matilija poppy you have observed. Ideally, your observation will include a closeup of an unopened bud. If the Matilija poppy you observed was planted (even if in a “natural area”), be sure to check the box for “Captive/Cultivated” to indicate it is not naturally occurring at that location.

The spectacular blooms of Matilija poppies prompted Mary Elizabeth Parsons to call R. coulteri “the queen of all our flowers” in her 1907 book The Wild Flowers of California. R. coulteri also has the distinction of having the largest flower of any native plant from California.