Dysphania is a genus of flowering plants in the family Amaranthaceae, order Caryophyllales, established by the Scottish botanist Robert Brown in 1810. The genus encompasses roughly 50–80 species of annual herbs and short-lived perennials distributed worldwide, from tropical and subtropical regions to warm-temperate zones on every inhabited continent.
Plants in the genus are characterised by stalked or sessile glandular hairs that give most species a pronounced aromatic or, to some, malodorous scent — a trait that has made several members economically significant as culinary and medicinal herbs. Stems are erect, ascending, decumbent, or prostrate and usually much-branched. The alternate leaves are mostly petiolate (upper leaves sometimes sessile), with blades ranging from linear and lanceolate to ovate or elliptic, often pinnately lobed, with entire, dentate, or serrate margins.
Inflorescences are terminal cymes or dense axillary glomerules, and flowers are small and bisexual (rarely unisexual), with up to five tepals fused only at the base or forming a sac, one to five stamens, and a superior ovary bearing one to three filiform stigmata. The fruit is a small utricle typically enclosed in the persistent perianth; seeds have a smooth or rugose coat and an annular embryo surrounding a copious farinose perisperm.
The most economically important member is Dysphania ambrosioides (L.) Mosyakin & Clemants (epazote), long used in Mexican and Central American cooking and traditional medicine. The genus also includes Dysphania botrys (Jerusalem oak) and Dysphania multifida, naturalised weeds in many temperate regions. Before molecular phylogenetic work in the 2000s, most species were placed in Chenopodium or the segregate genus Teloxys; the current circumscription was formalised by Mosyakin & Clemants (2002).
Etymology
The name Dysphania is derived from the Greek dys- (bad, difficult) and phainō (to appear, to show), referring to the inconspicuous, small flowers characteristic of the genus. The name was coined by Robert Brown in his 1810 Prodromus Florae Novae Hollandiae et Insulae Van Diemen.
Distribution
Dysphania is distributed worldwide across tropical, subtropical, and warm-temperate regions. In Europe, species occur as natives, archaeophytes, or naturalised introductions, becoming rare or absent in northern boreal regions. Several species — notably D. ambrosioides and D. botrys — have become widespread weeds outside their native ranges through human activity.
Taxonomy Notes
The genus was described by Robert Brown in 1810 (Prodr. Fl. Nov. Holland: 411) within Amaranthaceae (or the then-recognised Chenopodiaceae, now merged into Amaranthaceae). For much of the twentieth century most species were subsumed into the large genus Chenopodium; Mosyakin & Clemants (2002) re-established Dysphania as a distinct genus based on morphological and molecular evidence, transferring taxa such as Chenopodium ambrosioides to Dysphania ambrosioides. GBIF recognises the genus in Amaranthaceae, order Caryophyllales, with approximately 82 accepted species.
Cultural Uses
Several Dysphania species have long histories of human use. Dysphania ambrosioides (epazote) is a traditional culinary herb of Mexican and Central American cuisines, added to bean dishes, and used in folk medicine as an anthelmintic — a use reflected in its former scientific epithet anthelminticum. Dysphania botrys was similarly employed in European and Asian herbal medicine. The aromatic compounds responsible for these properties include ascaridole, a terpenoid peroxide found notably in D. ambrosioides.
