Theleaves are simple and mostly alternate, sometimes opposite. They never possessstipules. They are flat or terete, and their shape is extremely variable, with entire or toothed margins. In some species, the leaves are reduced to minute scales. In most cases, neither basal nor terminal aggregations of leaves occur.[3]
Theflowers are solitary or aggregated incymes,spikes, orpanicles and typically perfect (bisexual) andactinomorphic. Some species have unisexual flowers.Bracts andbracteoles are either herbaceous or scarious. Flowers are regular with an herbaceous or scarious perianth of (one to) mostly five (rarely to eight)tepals, often joined. One to fivestamens are opposite to tepals or alternating, inserting from a hypogynous disc, which may have appendages (pseudostaminodes) in some species. Theanthers have two or four pollen sacs (locules). In tribe Caroxyloneae, anthers have vesicular appendages. Thepollen grains are spherical with many pores (pantoporate), with pore numbers from a few to 250 (inFroelichia).[4] One to three (rarely six)carpels are fused to a superiorovary with one (rarely two) basal ovule.[3] Idioblasts are found in the tissues.
Thediaspores areseeds orfruits (utricles), more often the perianth persists and is modified in fruit for means of dispersal. Sometimes even bracts and bracteoles may belong to the diaspore. More rarely the fruit is a circumscissilecapsule or aberry. The horizontal or vertical seed often has a thickened or woody seed coat. The green or white embryo is either spirally (and withoutperisperm) or annular (rarely straight).[3]
Although most of the family use the more commonC3 photosynthesis pathway, around 800 species areC4 plants; this makes the Amaranthaceae the largest group with thisphotosynthesis pathway among theeudicots (which collectively includes about 1,600 C4 species).[5] Within the family, several types of C4 photosynthesis occur, and about 17 different types of leaf anatomy are realized. Therefore, this photosynthesis pathway seems to have developed about 15 times independently during the evolution of the family. About two-thirds of the C4 species belong to the former Chenopodiaceae. The first occurrence of C4 photosynthesis dates from the earlyMiocene, about 24 million years ago, but in some groups, this pathway evolved much later, about 6 (or less) million years ago.[5]
The multiple origin of C4 photosynthesis in the Amaranthaceae is regarded as an evolutionary response to inexorably decreasing atmospheric CO2 levels, coupled with a more recent permanent shortage in water supply as well as high temperatures. Species that use water more efficiently had a selective advantage and were able to spread out into arid habitats.[5]
Cladogram of Amaranthaceaes.l., modified and simplified, based on phylogenetic research of Müller & Borsch 2005, Kadereitet al. 2006, Sanchez del-Pino et al. 2009
In theAPG IV system of 2016, as in the previousAngiosperm Phylogeny Group classifications, the family is placed in the orderCaryophyllales and includes the plants formerly treated as the family Chenopodiaceae.[6] The monophyly of this broadly defined Amaranthaceae has been strongly supported by both morphological andphylogenetic analyses.[7]
The family Amaranthaceae was first published in 1789 byAntoine Laurent de Jussieu inGenera Plantarum, p. 87–88. The first publication of family Chenopodiaceae was in 1799 byÉtienne Pierre Ventenat inTableau du Regne Vegetal, 2, p. 253. The older name has priority and is now the valid scientific name of the extended Amaranthaceae (s.l. =sensu lato).
Some publications still continued to use the family name Chenopodiaceae.[8][9][10][11][12][13] Phylogenetic research revealed the important impact of the subfamilyPolycnemoideae on the classification (see cladogram): if Polycnemoideae are considered a part of Chenopodiaceae, then Amaranthaceae (s.str. =sensu stricto) have to be included, too, and the name of the extended family is Amaranthaceae. If Polycnemoideae would be separated as its own family, Chenopodiaceae and Amaranthaceae (s.str.) would form two distinctmonophyletic groups and could be treated as two separate families.
AmaranthaceaeJuss. (s.l.) includes the former families AchyranthaceaeRaf., AtriplicaceaeDurande, BetaceaeBurnett, BlitaceaeT.Post & Kuntze, CelosiaceaeMartynov, ChenopodiaceaeVent.nom. cons., CorispermaceaeLink, DeeringiaceaeJ.Agardh, Dysphaniaceae(Pax) Paxnom. cons., GomphrenaceaeRaf., PolycnemaceaeMenge, SalicorniaceaeMartynov, SalsolaceaeMenge, and SpinaciaceaeMenge.
The systematics of Amaranthaceae are the subject of intensive recent research. Molecular genetic studies revealed the traditional classification, based on morphological and anatomical characters, often did not reflect the phylogenetic relationships.
The former Amaranthaceae (in their narrow circumscription) are classified into two subfamilies,Amaranthoideae andGomphrenoideae, and contain about 65 genera and 900 species in tropicalAfrica andNorth America. The Amaranthoideae and some genera of Gomphrenoideae were found to bepolyphyletic, so taxonomic changes are needed.[14]
Amaranthaceae is a widespread andcosmopolitan family from the tropics to cool temperate regions. The Amaranthaceae (sensu stricto) are predominantly tropical, whereas the former Chenopodiaceae have their centers of diversity in dry temperate and warm temperate areas.[4] Many of the species arehalophytes, toleratingsalty soils, or grow in dry steppes or semi-deserts.
^abcde Kai Müller, Thomas Borsch (2005): Phylogenetics of Amaranthaceae using matK/trnK sequence data – evidence from parsimony, likelihood and Bayesian approaches. –Annals of the Missouri Botanical Garden,92, p. 66-102.
^abcGudrun Kadereit, Thomas Borsch, Kurt Weising, Helmut Freitag (2003): Phylogeny of Amaranthaceae and Chenopodiaceae and the evolution of C4 photosynthesis. –International Journal of Plant Sciences, Volume164 (6), p.959–986.
^Judd et al. (2008). Plant Systematics: A Phylogenetic Approach, Third Edition. Sinauer Associates, Inc. Sunderland, MA
^abHossein Akhani, Gerald Edwards, Eric H. Roalson (2007): Diversification Of The Old World Salsoleae s.l. (Chenopodiaceae): Molecular Phylogenetic Analysis Of Nuclear And Chloroplast Data Sets And A Revised Classification. –International Journal of Plant Sciences,168(6), p.931–956.
^abG. Kadereit, S. Hohmann, J.W. Kadereit (2006): A synopsis of Chenopodiaceae subfam. Betoideae and notes on the taxonomy of Beta. –Willdenowia36, p.9-19.
^abGudrun Kadereit, Ladislav Mucina, Helmut Freitag (2006): Phylogeny of Salicornioideae (Chenopodiaceae): diversification, biogeography, and evolutionary trends in leaf and flower morphology. –Taxon55(3), p. 617–642.
^Maxim V. Kapralov, Hossein Akhani, Elena V. Voznesenskaya, Gerald Edwards, Vincent Franceschi, Eric H. Roalson (2006): Phylogenetic Relationships in the Salicornioideae / Suaedoideae / Salsoloideae s.l. (Chenopodiaceae) Clade and a Clarification of the Phylogenetic Position of Bienertia and Alexandra Using Multiple DNA Sequence Datasets. –Systematic Botany.
^abGudrun Kadereit, Evgeny V. Mavrodiev, Elizabeth H. Zacharias, Alexander P. Sukhorukov (2010): Molecular phylogeny of Atripliceae (Chenopodioideae, Chenopodiaceae): Implications for systematics, biogeography, flower and fruit evolution, and the origin of C4 Photosynthesis. –American Journal of Botany97(10), p. 1664-1687.
^abGudrun Kadereit, Helmut Freitag (2011): Molecular phylogeny of Camphorosmeae (Camphorosmoideae, Chenopodiaceae): Implications for biogeography, evolution of C4-photosynthesis and taxonomy. –Taxon60(1), p. 51-78
^ Ivonne Sánchez del-Pino, Thomas Borsch, Timothy J. Motle (2009): trnL-F and rpl16 Sequence Data and Dense Taxon Sampling Reveal Monophyly of Unilocular Anthered Gomphrenoideae (Amaranthaceae) and an Improved Picture of Their Internal Relationships. –Systematic Botany, Volume34 (1), p. 57-67.doi:10.1600/036364409787602401
^Rüdiger Masson & Gudrun Kadereit (2013): Phylogeny of Polycnemoideae (Amaranthaceae): Implications for biogeography, character evolution and taxonomy.Taxon 62 (1): 100–111.[1]
^Alexander P. Sukhorukov (2007): Fruit anatomy and its taxonomic significance in Corispermum (Corispermoideae, Chenopodiaceae). –Willdenowia37,ISSN0511-9618, p.63-87,doi:10.3372/wi.37.37103
^Peter Schütze, Helmut Freitag, Kurt Weising (2003): An integrated molecular and morphological study of the subfamily Suaedoideae Ulbr. (Chenopodiaceae). –Plant Systematics and Evolution, Volume239, p. 257-286. abstract:doi:10.1007/s00606-003-0013-2
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