{{Short description|Genus of plants}} {{Speciesbox |image = Proatriplex pleiantha - Patrick Alexander 01.jpg |image_caption = ''Proatriplex pleiantha'' Sandoval County, New Mexico, USA | status = G3 | status_system = TNC | status_ref = <ref name=NS>{{cite web |title=''Proatriplex pleiantha'' {{!}} NatureServe Explorer |url=https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.135662/Proatriplex_pleiantha |website=NatureServe Explorer |access-date=2 October 2024}}</ref> |genus = Proatriplex |parent_authority = (W.A.Weber) Stutz & G.L.Chu |species = pleiantha |authority = (W.A.Weber) Stutz & G.L.Chu (1990) |display_parents = 3 |synonyms = *''Atriplex pleiantha'' <small>W.A.Weber (1950)</small> *''Atriplex'' subg. ''Proatriplex'' <small>W.A.Weber</small> *''Atriplex'' sect. ''Pleianthae'' <small>S.L.Welsh</small> |synonyms_ref = <ref name="Zacharias" /> }}
'''''Proatriplex''''' is a monotypic plant genus in the subfamily Chenopodioideae of the family Amaranthaceae, with the only species '''''Proatriplex pleiantha''''' (syn. ''Atriplex pleiantha'').<ref name="Zacharias" /> It is known by the common names '''four-corners orach'''<ref name="FlNAmerica" /> and '''Mancos shadscale'''.<ref>{{PLANTS|id=PRPL2|taxon=Proatriplex pleiantha|accessdate=14 October 2015}}</ref> It occurs in the Navajo Basin of Arizona, Colorado, New Mexico, and Utah.
==Description== thumb|left|''Proatriplex pleiantha'' detail of leaves and flowers ''Proatriplex pleiantha'' is an annual plant of 5–17 cm, glabrous, sometimes slightly farinose. The erect stems are branched from base with white-yellow or reddish ascending branches. The alternate or sometimes nearly opposite leaves are petiolate. The succulent, bright green leaf blades of 5–28 mm length and width are ovate to suborbiculate with entire margins. The leaf anatomy is of the "normal" (''non-Kranz'') type of C3-plants.<ref name="Zacharias" />
The plants are monoecious. The inflorescences either contain mixed male and female flowers, or consist of interrupted, terminal spikes of glomerulated male flowers, and female flowers standing in the leaf axils. Male flowers (without bracteoles) consist of 5 perianth lobes, ca. 1–1.5 mm long, united in the lower half, with cucullate tips, and 5 exserting stamens inserting on a disc. Female flowers are sitting in groups of 2–6 within 2 opposite bracteoles, they consist of a hyaline perianth of 5 scale-like, lanceolate to ovate tepals of 1–1.5 mm, and an ovary with 2 filiform, slightly exserted stigmas.<ref name="Zacharias" />
In fruit, the bracteoles enclosing the fruits become accrescent, 3–7 mm long and broad, slightly connate in the lower half. Their shape is triangular-ovate to orbiculate, with sessile or shortly stipitate bases and entire margins. Their surface is glabrous, without tubercles. The suborbicular to obovoid, laterally compressed fruit (utricle) is nearly equal in length to perianth and falls at maturity. The membranous pericarp adheres to the seed. The vertically orientated seed has a black, smooth and shining, crustaceous seed coat. The annular embryo surrounds the copious farinaceous perisperm.<ref name="Zacharias" />
''Proatriplex pleiantha'' is flowering from May to June.<ref name="Zacharias" />
The chromosome numbers are n = 9 (haploid) and 2n = 18 (diploid).<ref name="Zacharias" />
==Systematics== ''Proatriplex'' belongs to the tribe Atripliceae in the subfamily Chenopodioideae of the family Amaranthaceae.<ref name="Zacharias" />
''Proatriplex'' has been first described in 1950 by William Alfred Weber at the rank of a subgenus of ''Atriplex'' (in: ''Madroño'' 10(6): p. 188–189). In 1990, it was raised to genus level by Howard Coombs Stutz & Ge Lin Chu (in: ''American Journal of Botany'' 77(3), p. 364). The genus is monotypic, comprising only ''Proatriplex pleiantha'' (W.A. Weber) Stutz & G.L. Chu.. This species was later again included in genus ''Atriplex''.<ref name="FlNAmerica" /> Phylogenetic research revealed it to be distinct from most ''Atriplex'' species, being more closely related to other endemic North American genera of Atripliceae.<ref name="Zacharias" />
==Distribution== ''Proatriplex pleiantha'' is endemic to the Navajo Basin of Arizona, Colorado, New Mexico, and Utah. It is very common in desert badlands, and occurs often in pure stands on saline clay soils of depressions, or together with other halophytes in salt desert shrubs.<ref name="Zacharias" /> It grows at altitudes of 1400–1500 m.<ref name="FlNAmerica" />
==References== <references> <ref name="FlNAmerica">Stanley L. Welsh (2003): [http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=242415521 ''Atriplex pleiantha''] in Flora of North America, p.345</ref> <ref name="Zacharias">Elizabeth H. Zacharias, Bruce G. Baldwin (2010): ''A Molecular Phylogeny of North American Atripliceae (Chenopodiaceae), with Implications for Floral and Photosynthetic Pathway Evolution''. In: ''Systematic Botany'' '''35'''(4), p.839-857. {{doi|10.1600/036364410X539907}}</ref> </references>
==External links== {{Wikispecies|Proatriplex}} * {{GRIN genus|id=16074|name=''Proatriplex''}} * [http://www.tropicos.org/Name/40037128 ''Proatriplex''] at Tropicos
{{Taxonbar|from1=Q22986033|from2=Q6086963}}
Category:Chenopodioideae Category:Monotypic Amaranthaceae genera Category:Flora of Arizona Category:Flora of Colorado Category:Flora of New Mexico Category:Flora of Utah Category:Endemic flora of the United States Category:Plants described in 1950 Category:Taxa named by William Alfred Weber