''Diarthron'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...

in the family

Thymelaeaceae The Thymelaeaceae are a cosmopolitan family (biology), family of flowering plants composed of 50 genera (listed below) and 898 species.Zachary S. Rogers (2009 onwards)A World Checklist of Thymelaeaceae (version 1) Missouri Botanical Garden Webs ...

. The precise limits of the genus are uncertain. When broadly circumscribed to include ''Dendrostellera'' and ''Stelleropsis'', it consists of annual and perennial herbaceous plants and small shrubs, with reddish, white or green flowers lacking

petal Petals are modified leaves that form an inner whorl surrounding the reproductive parts of flowers. They are often brightly coloured or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''corol ...

s. It includes 16 species which range from southern European Russia and the Caucasus through Western and Central Asia through China and Mongolia to Korea and the Russian Far East.

Description

When broadly circumscribed (i.e. including ''Dendrostellera'' and ''Stelleropsis''), ''Diarthron'' is a genus of annual or perennial herbaceous plants or short deciduous shrubs. Prior to a review in 1982, only the annual species were placed in ''Diarthron'', with the perennial herbs being in ''Stelleropsis'' and the shrubs in ''Dendrostellera''. The flowers lack

s. There are usually four (sometimes five)

sepal A sepal () is a part of the flower of angiosperms (flowering plants). Usually green, sepals typically function as protection for the flower in bud, and often as support for the petals when in bloom., p. 106 Etymology The term ''sepalum'' ...

s, united at the base into a tube with lobes at the end, reddish, white or green in colour. The

ovary The ovary () is a gonad in the female reproductive system that produces ova; when released, an ovum travels through the fallopian tube/ oviduct into the uterus. There is an ovary on the left and the right side of the body. The ovaries are end ...

has a single chamber (

locule A locule (: locules) or loculus (; : loculi) is a small cavity or compartment within an organ or part of an organism (animal, plant, or fungus). In angiosperms (flowering plants), the term ''locule'' usually refers to a chamber within an ovary ...

). The fruit is dry with the seed enclosed in a thin glossy black

pericarp Fruits are the mature ovary or ovaries of one or more flowers. They are found in three main anatomical categories: aggregate fruits, multiple fruits, and simple fruits. Fruitlike structures may develop directly from the seed itself rather th ...

Taxonomy

The genus ''Diarthron'' was first described in 1832 by Nikolai Turczaninow for the species '' Diarthron linifolium''. Many species were added to the genus in 1982 by Kit Tan, being transferred from related genera. A 2006 study suggested that as circumscribed, ''Diarthron'' is not

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

, so that ''Dendrostellera'' and ''Stelleropsis'' which Tan had merged into ''Diarthron'' should be reinstated. Studies in 2002 and 2009, based on chloroplast DNA, placed ''Diarthron'' in a small group of related genera, sister to a clade consisting of ''

Thymelaea ''Thymelaea'' (the sparrow-worts) is a genus of about 30 species of evergreen shrubs and herbs in the flowering plant family Thymelaeaceae, native to the Canary Islands, the Mediterranean region, north to central Europe, and east to central Asia ...

'' and ''

Daphne Daphne (; ; , , ), a figure in Greek mythology, is a naiad, a variety of female nymph associated with fountains, wells, springs, streams, brooks and other bodies of freshwater. There are several versions of the myth in which she appears, but t ...

''; however for most genera only one species was included.

Species

16 species are currently accepted. *'' Diarthron altaicum'' (Thiéb.-Bern.) Kit Tan *'' Diarthron ammodendron'' (Kar. & Kir.) ined. *'' Diarthron antoniniae'' (Pobed.) Kit Tan *'' Diarthron arenarium'' (Pobed.) Kit Tan *'' Diarthron caucasicum'' (Pobed.) Kit Tan *'' Diarthron iranicum'' (Pobed.) Kit Tan *'' Diarthron issykkulense'' (Pobed.) Kit Tan *'' Diarthron lessertii'' (Wikstr.) Kit Tan *'' Diarthron linearifolium'' (Pobed.) Kit Tan *'' Diarthron linifolium'' Turcz. *'' Diarthron macrorhachis'' (Pobed.) Kit Tan *'' Diarthron magakjanii'' (Sosn.) Kit Tan *'' Diarthron tarbagataicum'' (Pobed.) Kit Tan *'' Diarthron tianschanicum'' (Pobed.) Kit Tan *'' Diarthron turkmenorum'' (Pobed.) Kit Tan *'' Diarthron vesiculosum'' (Fisch. & C.A.Mey.) C.A.Mey.

References

Thymelaeoideae Thymelaeaceae genera Paleotropical flora Taxa described in 1832 Taxa named by Nikolai Turczaninow {{Thymelaeaceae-stub