notes Characteristic long, single-stemed, stalk of Triodanis biflora, or ''Venus's Looking Glass''. The common name here is variously attributed to the mirror-like shininess of the seeds (e.g. see here) or simply to the loveliness of the flower itself. When I found & photographed this plant on 6/3/11 the species had not been previously recorded on the long-running plant list maintained by students and staff at the UC Big Creek Reserve, so I wanted to post this as a ''photo-voucher record'' of the occurrence there.
I've read that the lower flowers of Triodanis are cleistogamous. But earlier I was never clear on whether that meant all flowers below the terminal one—or if there may be numerous 'upper' flowers that are not cleistogamous and have large, showy, fully-opening corollas...perhaps opening sequentially one-at-a-time as the raceme grows. The few individuals of this species I've seen have had only a single, terminal, showy purple flower apparent when I encountered them.
Trying to answer this question, I searched for literature. The first item I found was the key here which indicates that T. biflora has ''one (rarely two) purple flowers opening at summit of stem (the lower flowers being cleistogamous)''. That seems(?) to imply there's usually only one (rarely two) corolla-bearing terminal flowers per plant. Indeed, having mostly corolla-less cleistogamous flowers with only a single showy terminal corolla during flowering might help explain why this annual is so infrequently noticed in the field! But it turn's out that's not the case...as seen in figures from the floras by Britton & Brown (see here) and Abrams (see Fig. 1091). Those figures show 2 (resp. 4) open (i.e. chasmogamous) flowers at the top of the spike. Interestingly, Britton & Brown's figures also show two fruits (one smaller) at a single node, though in the field only one would likely be immediately visible (the smaller likely hidden within the subtending bract).
Digging further into the literature, I found E. L. Greene's 1894 description of Triodonis , which states:
'Only the uppermost flowers complete, these with rotate 5-lobed corolla; the others apetalous, fertilized in bud. Calyx prismatic, of the apetalous flower 3-lobed, of the complete 5-lobed.'
The developing fruits at the lower nodes in my first two photos all have 3 vestigial calyx lobes...so from Greene's comments (reitereated in Abrams description) I guess they came from cleistogamous flowers in this individual. The figures from Britton & Brown and Abrams linked to above also show lower stem capsules topped with 3-lobed calyces...presumably arisen from cleistogamous flowers.
The most detailed account of Triodanis I found is the 1945 McVaugh paper. It indicates the cleistogamous flowers of T. biflora are only 0.5mm long!! Thus they would probably be completely overlooked without concerted effort using a hand-lens.
