Panarctic Flora

660101-02 The Urtica dioica aggregate U. dioica, U. gracilis

Geography: Circumboreal.

Notes: Korobkov (PAF proposal) accepted only one species of the Urtica dioica group to reach the Arctic: U. sondenii, with the North American name U. gracilis as a synonym. However, if U. sondenii (Simmons 1910) Avrorin ex Geltman 1988 and U. gracilis Aiton 1789 are merged, U. gracilis is the obvious priority name. If three species are accepted, the relevant names are U. dioica, U. gracilis, and U. sondenii. The North American U. gracilis is monoecious (male and female flowers on the same plant), whereas the Eurasian plants are dioecious (on different plants), one among several arguments in support of species rank for U. gracilis. Woodland et al. (1982) found good support for three independent complexes of perennial species of Urtica in North America, U. dioica (adventive) one of these, U. gracilis a member of a second group, i.e., they considered the two to be specifically well different. Native northern Eurasian plants ("sondenii") share some leaf and hair characters with U. gracilis but are almost always dioecious like European and western Siberian U. dioica s. str. Some authors treat these taxa as three subspecies (e.g., Selander 1947; Boufford 1997). We emphazise the difference in sex distribution and accept U. gracilis and U. dioica as two species, the latter with two subspecies.