Vernal pools are ephemeral habitats that form in winter and are completely dry by summer. They contain sufficient water in the spring to deter upland plants and are dry in the summer so no marsh plants survive. As a consequence unique and often rare plant species inhabit these seasonal pools.
Where Leonard and I live in Big Valley (Modoc County CA), this winter was unusually wet and chilly. The vernal pools are spectacular and contain many species that do not flower in drier years.
Bristled downingia (Downingia bicornuta), also commonly called doublehorn calicoflower, is a low-growing plant that blankets muddy wetlands and vernal pools. This annual native has simple, alternate, linear, cauline leaves on the branching stems. It germinates under water and when the vernal pool dries, the bristled downingia flowers bloom. There are several D bicornuta subspecies.
There are one or two blue to purple flowers atop each bristled downingia stem. The five petals are fused into a corolla tube terminating in two lobed lips. The upper lip has two, narrow pointed lobes. The three-lobed lower lip has a large white center with two yellow spots and two blue-purple nipple-like projections. The five stamens are fused into a central column topped by hooked anthers. Two large bristles (trigger hairs) at the tip of the lower two anthers may be twisted together or not. Five sepals surround the flower tube. The inferior ovary is long and resembles a pedicel.
Bristled downingia is pollinated by native, solitary bees. Cross-pollination must occur to produce seeds. The flower matures in stages to prevent self-pollination. The flower is first male and then becomes female. During the male stage, bees rub against the trigger hairs while searching for nectar, releasing the pollen. When these bees then visit a female bristled downingia the pollen rubs off onto the stigma.
Bristled downingia fruits are long, dehiscent (split along a line of weakness when mature) capsules. The seeds have longitudinal lines.
The species designation, bicornuta, is Latin for “two-horned” and refers to the trigger hairs. The genus name honors Andrew Jackson Downing (1815 – 1852), an American landscape designer.
Leonard and I observed these carpets of bristled downingia along the Pilot Butte Trail at Ash Creek Wildlife Area near Lookout CA.