The Polycnemoideae are a small subfamily of plants in the family

Amaranthaceae Amaranthaceae is a family of flowering plants commonly known as the amaranth family, in reference to its type genus '' Amaranthus''. It includes the former goosefoot family Chenopodiaceae and contains about 165 genera and 2,040 species, making i ...

, representing a basal evolutionary lineage. The few relictual species are distributed in Eurasia and North Africa, North America, and Australia.

Description

The subfamily Polycnemoideae comprises small herbs; some species are weakly lignified and grow shrublike. The subfamily is distinguishable from all other members of

by normal

secondary growth In botany, secondary growth is the growth that results from cell division in the cambia or lateral meristems and that causes the stems and roots to thicken, while primary growth is growth that occurs as a result of cell division at the tips ...

. The alternate or

opposite leaves In botany, phyllotaxis () or phyllotaxy is the arrangement of leaves on a plant stem. Phyllotactic spirals form a distinctive class of patterns in nature. Leaf arrangement The basic arrangements of leaves on a stem are opposite and alternat ...

are often linear or subulate. The stomata of the leaves are arranged in parallel to the midveins. The bisexual flowers are sitting solitary in the axil of a bract and two

bracteole In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves. They may be smaller, larger, or o ...

s. The inconspicuous

perianth The perianth (perigonium, perigon or perigone in monocots) is the non-reproductive part of the flower, and structure that forms an envelope surrounding the sexual organs, consisting of the calyx (sepals) and the corolla (petals) or tepals when ca ...

is formed of chartaceous, scarious, white or pinkish

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. One to five stamens are present with their filaments united in a short but distinct filament tube (like in subfamily Amaranthoideae). Anthers are with only one lobe and two pollen sacs (bilocular, like in subfamily Gomphrenoideae). In fruit, the tepals are never conspicuously modified.

Photosynthesis pathway

The Polycnemoideae are all C₃-plants. This is considered a primary character.

Distribution and evolution

The Polycnemoideae are distributed in the

temperate In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout t ...

regions of

Eurasia Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelag ...

(central and southern

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...

, northwestern

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

Central Asia Central Asia, also known as Middle Asia, is a region of Asia that stretches from the Caspian Sea in the west to western China and Mongolia in the east, and from Afghanistan and Iran in the south to Russia in the north. It includes the former ...

), North America, and Australia. Polycnemoideae began to diverge from Amaranthaceae s.str. in

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

. At the edge from Eocene to

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but ...

, the subfamily split into a lineage on the Northern Hemisphere, which was the ancestor of '' Polycnemum'', and a lineage predominantly occurring on the Southern Hemisphere with the ancestors of '' Nitrophila'', '' Hemichroa'', and '' Surreya''. An

antarctic The Antarctic ( or , American English also or ; commonly ) is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and o ...

connection of these southern ancestors is assumed. The genus Nitrophila developed in

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the souther ...

and dispersed later to North America. The genera of the subfamily diversified during

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recent" ...

and

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58

Systematics

The intrafamilial position of the Polycnemoideae has long been a matter of dispute. The taxon was recognized in 1827 as Tribus ''Polycnemeae'' within the family Chenopodiaceae by Dumortier ''(In Florula Belgica)''. Later, it was treated as belonging to the family Amaranthaceae in 1849 by Moquin-Tandon (in ''Prodromus systematis naturalis...''. Vol 13).

Oskar Eberhard Ulbrich Oskar Eberhard Ulbrich (17 September 1879 – 4 November 1952) was a German botanist and mycologist. Ulbrich was born in Berlin. He studied natural sciences at the University of Berlin, where his instructors included Adolf Engler (1844–1930) and ...

raised it to subfamilial level in 1934, again within Chenopodiaceae (in ''Engler & Prantl: Die natürlichen Pflanzenfamilien. Vol 16c''). Today, both families are included in Amaranthaceae ''s.l.''

Phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

research has revealed the Polycnemoideae represent a basal lineage of evolution within the family Amaranthaceae. The Polycnemoideae comprise only one tribe, Tribus Polycnemeae, with four genera and 13 species: * '' Hemichroa'' R.Br., with alternate, linear, succulent leaves, and stigmas papillous all around: only one species in Australia: ** ''

Hemichroa pentandra ''Hemichroa pentandra'', commonly known as trailing hemichroa, trailing saltstar or trailing jointweed, is a prostrate perennial herb in the amaranth family. It is endemic to Australia. A succulent halophyte, it grows to about 10 cm in ...

'' * '' Nitrophila'' S.Watson - niterwort, with opposite leaves, and stigmas papillous only on the inside, 4 species in North, Middle and South America: ** ''

Nitrophila atacamensis ''Nitrophila'' is a small genus of flowering plants in the Amaranthaceae, amaranth family sometimes known by the common name niterworts. The genus name is Greek for "soda-loving", as the plant grows in alkaline or salty soils, such as those rich ...

'' (Phil.) Ulbr. ** ''

Nitrophila australis ''Nitrophila'' is a small genus of flowering plants in the amaranth family sometimes known by the common name niterworts. The genus name is Greek for "soda-loving", as the plant grows in alkaline or salty soils, such as those rich in borax. The ...

'' Chodat & Wilczek ** '' Nitrophila mohavensis'' Munz & J.C. Roos - Amargosa niterwort ** '' Nitrophila occidentalis'' (Moq.) S. Watson - western niterwort, boraxweed * '' Polycnemum'' L., with alternate, subulate, non-succulent leaves, and stigmas papillous all around. 6 species in Eurasia (central and southern Europe, northwestern Africa, Central Asia): ** '' Polycnemum arvense'' L. - field needleleaf, soft needleleaf ** '' Polycnemum fontanesii'' Durieu & Moq. ** '' Polycnemum heuffelii'' Láng ** '' Polycnemum majus'' A. Braun ex Bogenh. - giant needleleaf ** '' Polycnemum perenne'' Litv. ** '' Polycnemum verrucosum'' Láng - warty needleleaf * '' Surreya'' R. Masson & G. Kadereit, two species in Australia: ** ''

Surreya diandra ''Surreya'' is a genus of flowering plants belonging to the family Amaranthaceae. It is also in the Polycnemoideae subfamily. It is native to Australia. The genus name of ''Surreya'' is in honour of Surrey Wilfrid Laurance Jacobs (1946–2009), ...

'' (R. Br.) R. Masson & G. Kadereit (Syn. ''Hemichroa diandra'' R. Br.) ** ''

Surreya mesembryanthema ''Surreya'' is a genus of flowering plants belonging to the family Amaranthaceae. It is also in the Polycnemoideae subfamily. It is native to Australia. The genus name of ''Surreya'' is in honour of Surrey Wilfrid Laurance Jacobs (1946–2009), ...

'' (R. Br.) R. Masson & G. Kadereit (Syn. ''Hemichroa mesembryanthema'' R. Br.)

References

Gudrun Kadereit, Thomas Borsch, K. Weising, and Helmut Freitag (2003): ''Phylogeny of Amaranthaceae and Chenopodiaceae and the evolution of C₄ photosynthesis''. - In: ''Int. J. Plant Sci.'' 164(6): p. 959–986. Rüdiger Masson & Gudrun Kadereit (2013): Phylogeny of Polycnemoideae (Amaranthaceae): Implications for biogeography, character evolution and taxonomy. ''Taxon'' 62 (1): 100-111

/ref> Polycnemoideae
Germplasm Resources Information Network - (GRIN) Online Database

External links

Polycnemoideae at Tropicos
{{Taxonbar, from=Q15930818 Amaranthaceae Caryophyllales subfamilies