Pholisma is a small genus of holoparasitic, desert-dwelling flowering plants belonging to the family Lennoaceae, placed within the order Boraginales. The genus is sometimes treated as part of a more broadly defined Boraginaceae. It comprises two to three species, all native to arid regions of the southwestern United States and northwestern Mexico, principally the Sonoran and Mojave deserts.
Unlike most flowering plants, Pholisma species completely lack chlorophyll and are incapable of photosynthesis. They are obligate root parasites, spending most of their lives underground as they attach to and draw nutrients from the roots of surrounding desert shrubs. The visible above-ground portion of the plant is largely limited to the flowering stem, which emerges briefly from the sand during the blooming season.
Morphologically, plants bear dense, scaly stems that can reach up to 1.5 m in length, with small glandular leaves 5–25 mm long, linear to triangular in shape. Flowers measure 7–10 mm and have stamens arranged in a single series. The fruit dehisces irregularly by circumscission below the middle. The genus name derives from the Greek word pholis, meaning scale, a reference to the distinctively scaly stem.
The best-known species is Pholisma sonorae, native to the Sonoran Desert of southwestern United States and Mexico. Pholisma arenarium, commonly called the "desert Christmas tree," is found in coastal and inland sandy habitats of southern California and Baja California. A third species, Pholisma culiacana, occurs in northwestern Mexico.
Etymology
The genus name Pholisma derives from the Greek word pholis, meaning "scale," a reference to the prominently scaly appearance of the plant's stem.
Distribution
Pholisma species are native to western Arizona, southern California, and northwestern Mexico, with the range centered on the Sonoran and Mojave deserts. Pholisma sonorae occurs across the wider Sonoran Desert into Mexico, while Pholisma arenarium is characteristic of coastal and sandy inland habitats in southern California and Baja California.
Ecology
Pholisma species are holoparasites that attach to the roots of a range of desert shrub hosts and obtain all nutrients from their host plants. They have no chlorophyll and perform no photosynthesis. Most of the plant's biomass remains subterranean; the flowering stem and inflorescence emerge above ground only briefly during the blooming period.
