{{Short description|Subfamily of flowering plants}} {{Automatic taxobox | image = Nitrophila occidentalis 2.jpg | image_caption = ''Nitrophila occidentalis'' | taxon = Polycnemoideae | authority = Ulbr. | subdivision_ranks = Genera | subdivision = 4 genera, see text }}

The '''Polycnemoideae''' are a small subfamily of plants in the family Amaranthaceae ''sensu lato''.<ref name=":0">{{Cite journal |last=Morales-Briones |first=Diego F |last2=Kadereit |first2=Gudrun |last3=Tefarikis |first3=Delphine T |last4=Moore |first4=Michael J |last5=Smith |first5=Stephen A |last6=Brockington |first6=Samuel F |last7=Timoneda |first7=Alfonso |last8=Yim |first8=Won C |last9=Cushman |first9=John C |last10=Yang |first10=Ya |date=2021-02-10 |editor-last=Ree |editor-first=Richard |title=Disentangling Sources of Gene Tree Discordance in Phylogenomic Data Sets: Testing Ancient Hybridizations in Amaranthaceae s.l |url=https://academic.oup.com/sysbio/article/70/2/219/5891675 |journal=Systematic Biology |language=en |volume=70 |issue=2 |pages=219–235 |doi=10.1093/sysbio/syaa066 |issn=1063-5157 |pmc=7875436 |pmid=32785686}}</ref> 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.<ref name="Kadereit" />

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.<ref name="Kadereit" />

== Photosynthesis pathway == The Polycnemoideae are all C<sub>3</sub>-plants. This is considered a primary character.<ref name="Kadereit" />

== Distribution and evolution == The Polycnemoideae are distributed in the temperate regions of Eurasia (central and southern Europe, northwestern Africa, Central Asia), North America, and Australia.<ref name="Kadereit" />

Polycnemoideae began to diverge from Amaranthaceae ''sensu stricto'' in the Eocene.{{Citation needed|date=January 2026}} At the edge from Eocene to Oligocene, the subfamily split into a lineage in 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''.{{Citation needed|date=January 2026}} An Antarctic connection of these southern ancestors is assumed.{{Citation needed|date=January 2026}} The genus Nitrophila developed in South America and dispersed later to North America.{{Citation needed|date=January 2026}} The genera of the subfamily diversified during Miocene and Pliocene, with only a few rare species that seem to be relictual.<ref name="Masson" />

== Systematics == [[File:Polycnemum arvense Sturm.png|thumb|''Polycnemum arvense'', Illustration]] 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 ''sensu lato''<ref name="Kadereit" />

Molecular phylogenetic studies have supported a variety of relationships between the Polycnemoideae and other members of the Amaranthaceae ''sensu lato'', with relationships dependent at least in part on the use of nuclear versus plastid gene markers.<ref name="Kadereit" /><ref>{{Cite journal |last=Müller |first=Kai |last2=Borsch |first2=Thomas |date=May 2005 |title=Phylogenetics of Amaranthaceae Based on matK/trnK Sequence Data: Evidence from Parsimony, Likelihood, and Bayesian Analyses |journal=Annals of the Missouri Botanical Garden |volume=92 |issue=1 |pages=66–102 |via=JSTOR}}</ref><ref>{{Cite journal |last=Hohmann |first=Sandra |last2=Kadereit |first2=Joachim W. |last3=Kadereit |first3=Gudrun |date=February 2006 |title=Understanding Mediterranean‐Californian disjunctions: molecular evidence from Chenopodiaceae‐Betoideae |url=https://onlinelibrary.wiley.com/doi/10.2307/25065529 |journal=Taxon |language=en |volume=55 |issue=1 |pages=67–78 |doi=10.2307/25065529 |issn=0040-0262|url-access=subscription }}</ref><ref>{{Cite journal |last=Kadereit |first=Gudrun |last2=Newton |first2=Rosemary J. |last3=Vandelook |first3=Filip |date=December 2017 |title=Evolutionary ecology of fast seed germination—A case study in Amaranthaceae/Chenopodiaceae |url=https://linkinghub.elsevier.com/retrieve/pii/S1433831917300677 |journal=Perspectives in Plant Ecology, Evolution and Systematics |language=en |volume=29 |pages=1–11 |doi=10.1016/j.ppees.2017.09.007|url-access=subscription }}</ref><ref>{{Cite journal |last=Walker |first=Joseph F. |last2=Yang |first2=Ya |last3=Feng |first3=Tao |last4=Timoneda |first4=Alfonso |last5=Mikenas |first5=Jessica |last6=Hutchison |first6=Vera |last7=Edwards |first7=Caroline |last8=Wang |first8=Ning |last9=Ahluwalia |first9=Sonia |last10=Olivieri |first10=Julia |last11=Walker‐Hale |first11=Nathanael |last12=Majure |first12=Lucas C. |last13=Puente |first13=Raúl |last14=Kadereit |first14=Gudrun |last15=Lauterbach |first15=Maximilian |date=March 2018 |title=From cacti to carnivores: Improved phylotranscriptomic sampling and hierarchical homology inference provide further insight into the evolution of Caryophyllales |url=https://bsapubs.onlinelibrary.wiley.com/doi/10.1002/ajb2.1069 |journal=American Journal of Botany |language=en |volume=105 |issue=3 |pages=446–462 |doi=10.1002/ajb2.1069 |issn=0002-9122|doi-access=free }}</ref><ref name=":0" /> Extensive phylogenetic hypothesis testing using both nuclear and plastic gene markers fails to resolve clear relationships between major clades within Amaranthaceae ''sensu lato'', including the Polycnemoideae; this discordance likely results primarily from rapid, ancient lineage diversification in the group.<ref name=":0" />

The Polycnemoideae comprise only one tribe, Polycnemeae,<ref name="GRIN" /> with four genera and 13 species:<ref name="Masson" /> * ''Hemichroa'' R.Br., with alternate, linear, succulent leaves, and stigmas papillous all around: only one species in Australia:<ref name="Masson" /> ** ''Hemichroa pentandra'' * ''Nitrophila'' S.Watson - niterwort, with opposite leaves, and stigmas papillous only on the inside, 4 species in North, Middle and South America:<ref name="Masson" /> ** ''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):<ref name="Masson" /> ** ''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'' L��ng - warty needleleaf * ''Surreya'' R. Masson & G. Kadereit, two species in Australia:<ref name="Masson" /> ** ''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 == <references> <ref name="Kadereit">Gudrun Kadereit, Thomas Borsch, K. Weising, and Helmut Freitag (2003): ''Phylogeny of Amaranthaceae and Chenopodiaceae and the evolution of C<sub>4</sub> photosynthesis''. - In: ''Int. J. Plant Sci.'' 164(6): p.&nbsp;959–986.</ref> <ref name="Masson">Rüdiger Masson & Gudrun Kadereit (2013): Phylogeny of Polycnemoideae (Amaranthaceae): Implications for biogeography, character evolution and taxonomy. ''Taxon'' 62 (1): 100-111. [http://www.ingentaconnect.com/content/iapt/tax/2013/00000062/00000001/art00009]</ref> <ref name="GRIN">[http://www.ars-grin.gov/cgi-bin/npgs/html/family.pl?2315 Polycnemoideae], Germplasm Resources Information Network - (GRIN) Online Database</ref> </references>

== External links == {{Commons category|Polycnemoideae}} {{Wikispecies|Polycnemoideae}} * [http://www.tropicos.org/Name/100385753 Polycnemoideae at Tropicos]

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Category:Amaranthaceae Category:Caryophyllales subfamilies Category:Taxa named by Oskar Eberhard Ulbrich