Acanthomintha, commonly known as thornmint or thorn-mint, is a small genus of four species in the mint family Lamiaceae. All species are endemic to the California Floristic Province of western North America, where they grow as aromatic annual wildflowers.
The genus is immediately recognisable by its spiny-margined leaves — the characteristic that gives both the scientific name (from the Greek for "thornmint") and the common name. Stems are erect and leaves are petioled with conspicuous veins. The inflorescences are compact, head-like clusters borne terminally on the stem. Flowers are funnel-shaped and consistently white, sometimes flushed with rose or lavender; the corolla is two-lipped, with a hooded upper lip and a reflexed, three-lobed lower lip, and a cream-coloured throat. The calyx also bears spine-tipped lobes. Each flower has four stamens, with the upper two reduced or sterile. Fruits are smooth, ovoid nutlets.
The genus comprises four described species, each restricted to a narrow geographic range within California: Acanthomintha duttonii (San Mateo County), which is federally listed as endangered; Acanthomintha ilicifolia (San Diego County and northern Baja California); Acanthomintha lanceolata (inner Coast Ranges from Alameda to San Luis Obispo counties); and Acanthomintha obovata (Alameda to Los Angeles counties). The small number of species and the narrow endemic ranges make this one of the more conservation-sensitive genera in the California flora.
Etymology
The genus name Acanthomintha derives directly from an identical Greek compound meaning "thornmint," a reference to the distinctively spiny-tipped leaf margins and calyx lobes that distinguish it from other members of the mint family.
Distribution
All four species are endemic to the California Floristic Province. Acanthomintha duttonii is confined to San Mateo County; A. ilicifolia occurs in San Diego County and just across the border into northern Baja California; A. lanceolata ranges along the inner Coast Ranges from Alameda County south to San Luis Obispo County; and A. obovata extends from Alameda County to Los Angeles County.
Conservation
Acanthomintha duttonii (San Mateo thorn-mint) is listed as an endangered species. The genus as a whole is notable for its extremely narrow endemic ranges within California, making all four species potentially vulnerable to habitat loss and land-use change in one of the world's recognised biodiversity hotspots.
