Asarum

Asarum is a genus of low-growing herbs distributed across the temperate zones of the Northern Hemisphere, with most species in East Asia (China, Japan, and Vietnam) 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, axillary, 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 carcinogen aristolochic acid.[1][2] [3] 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.

Asarum europaeum flower

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:

• Asarum sensu stricto (about 17 species), distributed in Asia (mainly China), North America, and Europe
• Heterotropa (about 50 species), distributed in Asia
• Asiasarum (three or four species), distributed in Asia
• Geotaenium (three or four species), distributed in Asia
• Hexastylis (ten species), distributed in North America

Study of the internal transcribed spacer region (ITS) 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.[4]

• Asarum sensu stricto (s.s.) : the North American species are monophyletic and are derived from within the paraphyletic Asian species group.
• Geotaenium is a sister to Asarum s.s., showing its close relationship to Asarum s.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.[5] 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 Asarum sensu lato, especially Hexastylis.[6]

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• Takashi Sugawara (1982). "Taxonomic studies of Asarum sensu lato". Journal of Plant Research. 95 (3): 295–302. doi:10.1007/bf02488540. S2CID 115785096.
• Lawrence M. Kelly (2001). "Taxonomy of Asarum Section Asarum (Aristolochiaceae)". Systematic Botany. 26 (1): 17–53. doi:10.1043/0363-6445-26.1.17 (inactive 2021-01-14).CS1 maint: DOI inactive as of January 2021 (link)
• List of Asarum species
• The International Agency for Research on Cancer.