Pholistoma is a small genus of flowering annual herbs in the family Hydrophyllaceae, placed within the order Boraginales. Commonly known as fiestaflowers, the genus comprises three accepted species, all native to a stretch of western North America reaching from Oregon south through California to Baja California, Mexico.
Plants in this genus are fleshy annuals that develop angled, bristly or prickly stems with several brittle branches. The leaves are deeply lobed and bristly, borne on distinctively winged petioles that clasp the stem at their bases — a characteristic feature that helps distinguish fiestaflowers in the field. Flowers are rotate (wheel-shaped) and appear in shades of blue, purple, or white, the exact color depending on the species.
The three accepted species are Pholistoma auritum (Lindl.) Lilja (blue fiestaflower), Pholistoma membranaceum (Benth.) Constance (white fiestaflower), and Pholistoma racemosum (Nutt. ex A.Gray) Constance (racemose fiestaflower). The family Hydrophyllaceae is sometimes treated as a subfamily of Boraginaceae in broader circumscriptions, though GBIF retains it as a distinct family.
Etymology
The name Pholistoma derives from Greek roots — pholis (scale) and stoma (mouth) — likely referring to a scaled or toothed feature of the flower or calyx. Species epithets reflect morphology or habit: auritum (eared), membranaceum (membranous), and racemosum (having racemes).
Distribution
Pholistoma is endemic to a narrow corridor of western North America, with all three species occurring between Oregon and Baja California, Mexico. The genus is characteristic of California's varied terrain and extends into adjacent regions along the Pacific slope.
Ecology
Fiestaflowers are annual herbs adapted to open, often disturbed habitats in western North America, including chaparral margins, roadsides, and shaded canyon slopes. Their bristly, clinging stems allow them to scramble over adjacent vegetation.
