Observations of the Month: Owl's-Clover (Orobanchaceae)

Purple Owl’s-Clover (Castilleja exserta subsp. exserta) https://www.inaturalist.org/observations/40729470 by jrebman
Parish’s or Graceful Owl’s-Clover (Castilleja densiflora subsp. gracilis) https://www.inaturalist.org/observations/39212245 by jrebman

In San Diego County, we have two kinds of Owl’s-Clover that are annuals with mostly pinkish-purple inflorescences: Purple Owl’s-Clover (Castilleja exserta subsp. exserta) and Parish’s or Graceful Owl’s-Clover (Castilleja densiflora subsp. gracilis). Both plants are widespread in our county, but Castilleja exserta subsp. exserta is more common and ranges farther inland than Castilleja densiflora subsp. gracilis. When you examine either of these plants, it can be difficult to figure out the parts of the flowers. Forget easily recognized structures like petals and sepals. Instead, you need to become conversant with lips and beaks.

The 5 petals of each of these two taxa are fused, forming corolla lips. One of the more obvious features of the plants are the shorter, pouch-like, 3-lobed lower corolla lips that are usually pinkish below and white with yellow and darker purplish markings at the top. In Castilleja exserta subsp. exserta this lip is rather subdued, but in Castilleja densiflora subsp. gracilis the lower corolla lip is widened and appears to bulge out. (Occasionally, you may find “albino” plants with the pinkish parts replaced with white, but usually those plants are mixed in with more typically colored ones.)

(L) Castilleja exserta subsp. exserta (R) Castilleja densiflora subsp. gracilis © Jon Rebman

The beak is the fusion of the 2 upper petals and in both of these species is pinkish and projects above the lower corolla lip. In Castilleja exserta subsp. exserta the beak is “shaggy hairy” and is hooked at the end and the stigma appears to be perched below the hook. In Castilleja densiflora subsp. gracilis the beak is much less hairy, straight, and the stigma appears to be perched at the tip.

When you post an observation of one of these plants, be sure to include a close-up, side view photo of the beak and corolla lip as the first photo in the observation for ease of identification.

Posted on 27 de março de 2020, 06:42 PM by milliebasden