Athysanus is a small genus of annual flowering plants in the mustard family (Brassicaceae), order Brassicales. It contains just two accepted species, both native to the Pacific Coast region of western North America, ranging from British Columbia in Canada south through California to Baja California, Mexico.
Plants in this genus are low-growing annuals, either glabrous or bearing a mixture of simple and branched (forked, 3-rayed, or cruciform) trichomes. Stems arise in small numbers from the base and are ascending and branched. The leaves are both basal and cauline; basal leaves are shortly petiolate with entire or dentate blade margins, while cauline leaves are petiolate to sessile with bases that are not auriculate.
The inflorescence is a corymbose raceme — several-flowered, secund, and lax — that elongates considerably in fruit. Fruiting pedicels are recurved or reflexed. Flowers may be cleistogamous (self-pollinating without opening) and/or chasmogamous (open-pollinating). Petals are white and often rudimentary, occasionally well-developed and exceeding the sepals. Stamens are subequal, with ovate to globose anthers.
The fruit is a silicle — a short, broad seed pod — that is pendulous, indehiscent or only very tardily dehiscent, sessile, and typically orbicular to obovate-elliptic in outline, sometimes twisted or flattened, with a latiseptate structure. Each ovary contains 2–12 ovules. Seeds are uniseriate, flattened, and oblong, with accumbent cotyledons.
The two species are Athysanus pusillus (Hook.) Greene, found from western Canada south to Baja California, and Athysanus unilateralis (M.E. Jones) Jeps., ranging from Oregon to northern Baja California. The genus was established by Edward Lee Greene and published in his Manual of the Botany of the Region of San Francisco Bay (1894).
Etymology
The genus name Athysanus is of Greek origin, though the specific derivation is not documented in available sources. The genus was named and published by the American botanist Edward Lee Greene in 1894 in his Manual of the Botany of the Region of San Francisco Bay.
Distribution
Athysanus is native to the Pacific Coast of western North America. Athysanus pusillus ranges from British Columbia, Canada, south to Baja California, Mexico. Athysanus unilateralis has a more southerly distribution, from Oregon to northern Baja California.
Taxonomy Notes
The genus Athysanus Greene was published in Man. Bot. San Francisco: 14 (1894) and is placed in the family Brassicaceae, order Brassicales. It comprises two accepted species. Flowers in the genus may be cleistogamous (closed, self-fertilizing) and/or chasmogamous (open), a functionally notable trait within the Brassicaceae.
