The Polycnemoideae are a small subfamily of plants in the family Amaranthaceae, 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 Amaranthaceae by normal secondary growth. The alternate or opposite leaves 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 bracteoles. The inconspicuous perianth is formed of chartaceous, scarious, white or pinkish tepals. 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 (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ran ...

regions of

Eurasia Eurasia ( , ) is a continental area on Earth, comprising all of Europe and Asia. According to some geographers, Physical geography, physiographically, Eurasia is a single supercontinent. The concept of Europe and Asia as distinct continents d ...

(central and southern

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

, northwestern

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

Central Asia Central Asia is a region of Asia consisting of Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan. The countries as a group are also colloquially referred to as the "-stans" as all have names ending with the Persian language, Pers ...

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

, and

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

. Polycnemoideae began to diverge from Amaranthaceae s.str. in

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

. At the edge from Eocene to

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

, the subfamily split into a lineage on the

Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...

, 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 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 considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

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

Miocene The Miocene ( ) is the first epoch (geology), 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 mea ...

and

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 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 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 () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

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'' * '' Nitrophila'' S.Watson - niterwort, with opposite leaves, and stigmas papillous only on the inside, 4 species in North, Middle and South America: ** '' Nitrophila atacamensis'' (Phil.) Ulbr. ** '' Nitrophila australis'' 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'' (R. Br.) R. Masson & G. Kadereit (Syn. ''Hemichroa diandra'' R. Br.) ** '' Surreya mesembryanthema'' (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 Taxa named by Oskar Eberhard Ulbrich