Asarum is a genus of low-growing herbs distributed across the temperate zones of the Northern Hemisphere, with most species in East Asia and North America, and one species in Europe. Biogeographically, Asarum originated in Asia. They have characteristic kidney-shaped leaves, growing from creeping rhizomes, and bear small, lary, brown or reddish flowers. The plant is called wild ginger because the rhizome tastes and smells similar to ginger root, but the two are not particularly related. The FDA warns against consuming Asarum, as it is nephrotoxic and contains the potent carcinogenaristolochic acid. The birthwort family also contains the genus Aristolochia, known for carcinogens. Wild ginger favors moist, shaded sites with humus-rich soil. The deciduous, heart-shaped leaves are opposite, and borne from the rhizome which lies just under the soil surface. Two leaves emerge each year from the growing tip. The curious jug-shaped flowers, which give the plant an alternate name, little jug, are borne singly in spring between the leaf bases. Wild ginger can easily be grown in a shade garden, and makes an attractive groundcover. '' flower
Taxonomy
Traditionally, the genus Asarum was considered as a single genus with about 85 species. However, a trend exists among some botanists to segregate the genus into separate genera, based on considerations of chromosome number and floral morphology:
Asarumsensu stricto, distributed in Asia, North America, and Europe
Heterotropa, distributed in Asia
Asiasarum, distributed in Asia
Geotaenium, distributed in Asia
Hexastylis , distributed in North America
Study of the internal transcribed spacer region of nuclear ribosomal DNA, combined with morphological data, has yielded a better-resolved phylogenetic hypothesis, supporting a recognition of two subgenera, Asarum and Heterotropa each containing two sections, rather than the segregated genera above.
Geotaenium is a sister to Asarums.s., showing its close relationship to Asarums.s..
Asiasarum is a sister to the Hexastylis + Heterotropa clade, showing several synapomorphies with this clade.
Hexastylis: this genus has been recognized solely on the study by H.L. Blomquist. However, the above-mentioned DNA study provided indications that Hexastylis is not monophyletic and that some species of Hexastylis are more closely related to Asiatic species of Heterotropa than they are to other species of Hexastylis.
Heterotropa: this is a complex monophyletic group, well nested within the Asiasarum + Hexastylis + Heterotropa clade
Therefore, many botanists still treat these segregated genera as subgenera and sections of Asarumsensu lato, especially Hexastylis.
