Muehlenbeckia
Muehlenbeckia or maidenhair is a genus of flowering plants in the family Polygonaceae. It is native to the borders of the Pacific, including South and North America, Papua New Guinea and Australasia. It has been introduced elsewhere, including Europe. Species vary in their growth habits, many being vines or shrubs. In some environments, rampant species can become weedy and difficult to eradicate. Description. Species of "Muehlenbeckia" vary considerably in their growth habits; they may be perennials, vinelike, or shrubs. All have rhizomatous roots. Their leaves are arranged alternately on the stem, usually with stalks (petioles), but sometimes stalkless (sessile ). The brownish ocrea is short and tubular, soon disintegrating. The inflorescences may be terminal or axillary, and are in the form of spikes or clusters, with at most very short peduncles (flowering stems). Individual flowers have pedicels (stalks). The flowers may be bisexual or unisexual, with sometimes a mixture of staminate, pistillate and bisexual flowers on the same plant. There are five white to greenish white tepals, joined at the base. Staminate flowers have 8 (sometimes 9) stamens and a rudimentary pistil. Pistillate flowers have rudimentary stamens and three spreading styles. The fruit is in the form of a black  or dark brown unwinged achene, three-sided to more or less globe-shaped, at least partly enclosed by the persistent tepals. Taxonomy. The genus was erected by Carl Meissner in 1841, initially for two species that he distinguished from "Coccoloba" and "Polygonum". The generic name honours Alsatian bryologist Heinrich Gustav Mühlenbeck (1798–1845). "Muehlenbeckia" is placed in the tribe Polygoneae of the subfamily Polygonoideae. Within the tribe, it is most closely related to the genera "Reynoutria" and "Fallopia" s.s., forming the so-called "RMF clade". Species. , Plants of the World Online recognized 24 species (see note below): Some sources, including Plants  of the World Online, regard "M. adpressa" as a synonym of "M. australis". Others treat them as separate species. Three species have been transferred to the genus "Duma": Invasiveness. All members of the RMF clade appear to have the potential to become invasive, in some cases via vigorous hybrids. The highly invasive Japanese knotweed ("Reynoutria japonica") hybridizes with "Muehlenbeckia australis". The related "Muehlenbeckia complexa" has established populations in southern parts of Britain and in the Channel Islands, and is a problematic invasive species in the San Francisco area.