''Pteroxygonum'' is a plant genus in the family

Polygonaceae The Polygonaceae are a family of flowering plants known informally as the knotweed family or smartweed—buckwheat family in the United States. The name is based on the genus ''Polygonum'', and was first used by Antoine Laurent de Jussieu in 1789 ...

. , two species are recognized. Their native range is from

Tibet Tibet (; ''Böd''; ) is a region in East Asia, covering much of the Tibetan Plateau and spanning about . It is the traditional homeland of the Tibetan people. Also resident on the plateau are some other ethnic groups such as Monpa people, ...

to southeast China.

Description

Species of ''Pteroxygonum'' are twining

vine A vine (Latin ''vīnea'' "grapevine", "vineyard", from ''vīnum'' "wine") is any plant with a growth habit of trailing or scandent (that is, climbing) stems, lianas or runners. The word ''vine'' can also refer to such stems or runners themselv ...

s growing from a large woody globe-shaped

tuber Tubers are a type of enlarged structure used as storage organs for nutrients in some plants. They are used for the plant's perennation (survival of the winter or dry months), to provide energy and nutrients for regrowth during the next growing ...

. Their leaves are broad and palmate, with a dark red mark around each primary leaf vein. The

inflorescence An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Morphologically, it is the modified part of the shoot of seed plants where flowers are formed o ...

is in the form of an axillary

raceme A raceme ( or ) or racemoid is an unbranched, indeterminate type of inflorescence bearing flowers having short floral stalks along the shoots that bear the flowers. The oldest flowers grow close to the base and new flowers are produced as the s ...

. The flowers are

bisexual Bisexuality is a romantic or sexual attraction or behavior toward both males and females, or to more than one gender. It may also be defined to include romantic or sexual attraction to people regardless of their sex or gender identity, whi ...

, with five spirally arranged

tepal A tepal is one of the outer parts of a flower (collectively the perianth). The term is used when these parts cannot easily be classified as either sepals or petals. This may be because the parts of the perianth are undifferentiated (i.e. of very ...

s, eight

stamen The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filame ...

s joined at the base, and three

style Style is a manner of doing or presenting things and may refer to: * Architectural style, the features that make a building or structure historically identifiable * Design, the process of creating something * Fashion, a prevailing mode of clothing ...

s, also joined up to about the middle.

Nectar Nectar is a sugar-rich liquid produced by plants in glands called nectaries or nectarines, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualists ...

is produced from tissue at the base of the staments. Their fruits are in the form of winged, three-angled

achene An achene (; ), also sometimes called akene and occasionally achenium or achenocarp, is a type of simple dry fruit produced by many species of flowering plants. Achenes are monocarpellate (formed from one carpel) and indehiscent (they do not ope ...

Taxonomy

The genus ''Pteroxygonum'' was erected in 1905 by Carl Dammer and F. Ludwig Diels for the species ''

Pteroxygonum giraldii ''Pteroxygonum giraldii'' is a species of flowering plant in the family Polygonaceae, endemic to the China, Chinese provinces of Gansu, Hebei, Henan, Hubei, Shaanxi, Shanxi, and Sichuan. It is found at altitudes of . It grows to more than in hei ...

''. They separated ''Pteroxygonum'' from ''Polygonum'' on the basis of the "very notably different structure of the fruit". Until 2015, the genus was considered to contain only this species. A 2015

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

study found that the species formerly called ''Polygonum denticulatum'' was closely related to ''Pteroxygonum giraldii'', and accordingly moved it to ''Pteroxygonum''. ''Pteroxygonum'' is placed in the subfamily

Polygonoideae Polygonoideae is a subfamily of plants in the family Polygonaceae. It includes a number of plants that can be highly invasive, such as Japanese knotweed, ''Reynoutria japonica'', and its hybrid with '' R. sachalinensis'', ''R.'' × ''bohemica'' ...

, tribe Pteroxygoneae. Some species assigned to the genus ''

Fallopia ''Fallopia'' is a genus of about 12 species of flowering plants in the buckwheat family, often included in a wider treatment of the related genus ''Polygonum'' in the past, and previously including ''Reynoutria''. The genus is native to temperat ...

'' were placed alongside ''Pteroxygonum'' in the cladogram resulting from the 2015 study, and may belong to a new genus.

Species

Plants of the World Online Plants of the World Online (POWO) is an online database published by the Royal Botanic Gardens, Kew. It was launched in March 2017 with the ultimate aim being "to enable users to access information on all the world's known seed-bearing plants by ...

accepted two species: *'' Pteroxygonum denticulatum'' (C.C.Huang) T.M.Schust. & Reveal *''

'' Dammer & Diels

References

Bibliography

* "Reappraisal of the generic status of ''Pteroxygonum'' (Polygonaceae) on the basis of morphology, anatomy and nrDNA ITS sequence analysis", Wei SUN et al., ''Journal of Systematics and Evolution'' 46 (1): 73–79 (2008)

eFloras description
{{Commons category Polygonoideae Polygonaceae genera Taxa named by Carl Lebrecht Udo Dammer Taxa named by Ludwig Diels