popcorn flowers

genus Plagiobothrys

Member of popcorn flowers and cryptanthas
borage family (family Boraginaceae)
borages (order Boraginales)
dicots (class Magnoliopsida)
flowering plants (subphylum Angiospermae)

Except for old historical records and extremely rare examples that I don't expect to encounter, there are no other wild species of this genus in the bay area.
Caution: The key to distinguish these species is not complete.

popcorn flowers and cryptanthas are difficult to distinguish between and among each other except by minute features of their nutlets. Nutlets may be found within the older (proximal) calyxes while younger flowers bloom above.

Key features:

stem erect, decumbent, or prostrate
lower cauline leaves alternate or opposite (upper cauline leaves may differ)
basal leaves present, withered, or gone
color of abaxial leaf midveins and margins, staining or not
number and position of bracts
inflorescence strongly coiled toward tip or not
petal diameter (of the roundish, spreading portion of an individual petal beyond the corolla throat); earlier (proximal) flowers tend to be larger and later (distal) flowers smaller
color of raised corolla appendages (at the junction of corolla limbs where petals merge)
calyx length, hair color, base fleshy, lobe shape, lobes bent or straight [generally upward], lobe midvein stout or slender
pedicel length, thick & hollow or slender and solid

Jepson mentions “appendages yellow” for some flowers, but a genus note says “Yellow corolla appendages and [...] yellow corolla centers change to white after successful pollination.”