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

Polygonaceae The Polygonaceae are a Family (biology), family of flowering plants known Common name, informally as the knotweed family or smartweed—buckwheat family in the United States. The Botanical name, name is Basionym, based on the genus ''Polygonum'', ...

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

Tibet Tibet (; ''Böd''; ), or Greater Tibet, is a region in the western part of East Asia, covering much of the Tibetan Plateau and spanning about . It is the homeland of the Tibetan people. Also resident on the plateau are other ethnic groups s ...

to southeast China.

Description

Species of ''Pteroxygonum'' are twining

vine A vine 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 themselves, for instance, when used in wicker work.Jackson; Benjamin; Da ...

s growing from a large woody globe-shaped

tuber Tubers are a type of enlarged structure that plants use as storage organs for nutrients, derived from stems or roots. Tubers help plants perennate (survive winter or dry months), provide energy and nutrients, and are a means of asexual reproduc ...

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

inflorescence In botany, an inflorescence is a group or cluster of flowers arranged on a plant's Plant stem, stem that is composed of a main branch or a system of branches. An inflorescence is categorized on the basis of the arrangement of flowers on a mai ...

is in the form of an axillary

raceme A raceme () or racemoid is an unbranched, indeterminate growth, 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 ...

. The flowers are

bisexual Bisexuality is romantic attraction, sexual attraction, or sexual behavior toward both males and females. It may also be defined as the attraction to more than one gender, to people of both the same and different gender, or the attraction t ...

, 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 (: stamina or stamens) is a part consisting of the male reproductive organs of a flower. Collectively, the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filament ...

s joined at the base, and three

style Style, or styles may refer to: Film and television * ''Style'' (2001 film), a Hindi film starring Sharman Joshi, Riya Sen, Sahil Khan and Shilpi Mudgal * ''Style'' (2002 film), a Tamil drama film * ''Style'' (2004 film), a Burmese film * '' ...

s, also joined up to about the middle.

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

is produced from tissue at the base of the stamens. 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 fruit, simple dry fruits, dry fruit produced by many species of flowering plants. Achenes are monocarpellate (formed from one carpel) and Dehi ...

Taxonomy

The genus ''Pteroxygonum'' was erected in 1905 by Carl Dammer and F. Ludwig Diels for the species '' Pteroxygonum giraldii''. 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 taxonomic database published by the Royal Botanic Gardens, Kew. History Following the Convention on Biological Diversity, the Royal Botanic Gardens in Kew launched Plants of the World Online i ...

accepted two species: *'' Pteroxygonum denticulatum'' (C.C.Huang) T.M.Schust. & Reveal *'' Pteroxygonum giraldii'' 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
{{Taxonbar, from1=Q7256971 Polygonoideae Polygonaceae genera Taxa named by Carl Lebrecht Udo Dammer Taxa named by Ludwig Diels