Atriplex

Atriplex patula, female flower with bracteoles and seed

The species in genus Atriplex are annual or perennial herbs, subshrubs, or shrubs. The plants are often covered with bladderlike hairs, that later collapse and form a silvery, scurfy or mealy surface, rarely with elongate trichomes. The alternate or rarely opposite leaves are petiolate or sessile, often persistent or tardily deciduous. The flat or slightly fleshy leaf blades are either entire, or serrate, or lobed and very variable in shape.[4][5]

The inflorescences consist of axillary or terminal spikes or spicate panicles, or axillary clusters of glomeruled flowers. The flowers are unisexual, some species are monoecious, others dioecious. Male flowers consist of 3-5 perianth lobes and 3-5 stamens. Female flowers are usually lacking a perianth, but are enclosed by 2 foliaceous bracteoles, and contain an ovary with a short style and 2 stigmas.[4][5]

In fruit, the bracteoles can enlarge, thicken or become appendaged. They enclose the fruit tightly, without becoming connate to it. The pericarp is adnate to the vertically orientated, flattened seed. The seed coat is thick, leathery or hardening. The annular embryo surrounds the perisperm.[4][5]

The chromosome base number is x = 9, except for Atriplex lanfrancoi, which is x=10.[6]

A few Atriplex species are C₃-plants, but most species are C₄-plants, with a characteristic leaf anatomy (kranz anatomy).[6]

The genus Atriplex is distributed nearly worldwide from subtropical to temperate and to subarctic regions. Most species-rich are Australia, North America, South America and Eurasia. Many species are halophytes and are adapted to dry environments with salty soils.[6]

The genus evolved in Middle Miocene, the C₄-photosynthesis pathway developed about 14.1-10.9 million years ago, when the climate became increasingly dry. The genus diversified rapidly and spread over the continents. The C₄Atriplex colonized North America probably from Eurasia during the Middle/Late Miocene, about 9.8-8.8 million years ago, and later spread to South America. Australia was colonized twice by two C₄ lineages, one from Eurasia or America about 9.8-7.8 million years ago, and one from Central Asia about 6.3-4.8 million years ago. The last lineage diversified rapidly, and became the ancestor of most Australian Atriplex species.[6]

Atriplex species are used as food plants by the larvae of some Lepidoptera species; see the list of Lepidoptera which feed on Atriplex.[7] For spiders such as Phidippus californicus and other arthropods, saltbush plants offer opportunities to hide and hunt in habitat that is otherwise often quite barren.

It has been proposed that genus Atriplex was a main food source in the diet of the extinct giant kangaroo Procoptodon goliah.[8] Stable isotopic data suggested that their diet consisted of plants that used the C4 photosynthetic pathway, and due to their semi-arid distribution, chenopod saltbushes were likely responsible.[9][10][11]

The favored species for human consumption is now usually garden orache (A. hortensis),[12][13][14] but many species are edible and the use of Atriplex as food is known since at least the late Epipaleolithic (Mesolithic).

Common orache (A. patula) is attested as an archaeophyte in northern Europe, and the Ertebølle culture is presumed to have used it as a food.[15] Its seed has been found among apparent evidence of cereal preparation and cooking at Late Iron Age villages in Britain.[16] In the biblical Book of Job, mallûaḥ (מַלּ֣וּחַ, probably Mediterranean saltbush, A. halimus, the major culinary saltbush in the region) is mentioned as food eaten by social outcasts (Job 30:4[17]). Grey saltbush (A. cinerea) has been used as bushfood in Australia since prehistoric times. Chamiso (A. canescens) and shadscale (A. confertifolia) were eaten by Native Americans, and spearscale (A. hastata) was a food in rural Eurasia.

Studies on Atriplex species demonstrated their potential use in agriculture. Meat from sheep which have grazed on saltbush has surprisingly high levels of vitamin E, is leaner and more hydrated than regular lamb and has consumer appeal equal to grain-fed lamb.[18] The vitamin E levels could have animal health benefits while extending the shelf-life and maintaining the fresh red colour of saltbush lamb. This effect has been demonstrated for old man saltbush (A. nummularia) and river saltbush (A. amnicola). For reasons unknown, sheep seem to prefer the more fibrous, less nutritious river saltbush.[19][18]

A study on Atriplex nummularia discovered the species have a nitrogen content of 2.5-3.5%, and could potentially be used as a protein supplement for grazing if palatable.[20] A subsequent study allowed sheep and goats to voluntarily feed on Atriplex halimus and aimed to determine if the saltbush was palatable, and if so, did it provide enough nutrients to supplement the diet of these animals.[21] In this study they determined when goats and sheep are given as much A. halimus as they like, they do obtain enough nutrients to supplement their diet – unless the animal requirements are higher during pregnancy and milk production.

Saltbushes are also used as an ornamental plant in landscaping and can be used to prevent soil erosion in coastal areas.[22][23] Old man saltbush (Atriplex nummularia) has also been successfully used to rehabilitate old mining sites around Lightning Ridge (Australia).

• 
  Atriplex elegans
• 
  Atriplex hymenelytra
• 
  Atriplex latifolia
• 
  Atriplex lentiformis
• 
  Atriplex nummularia
• 
  Atriplex suberecta

The genus Atriplex was first described in 1753 by Carl Linnaeus.[24] The type species (lectotype) is Atriplex hortensis.[25] The name is derived from Ancient Greek ἀτράφαξυς (atraphaxys), "orach", itself a Pre-Greek substrate loanword.

Atriplex is an extremely species-rich genus and comprises about 250[5]-300[6] species.

Traditional taxonomy of Atripliceae based on morphological features has been controversial.[26] Molecular studies have found that many genera are not true clades. One such study found that Atripliceae could be divided into two main clades, Archiatriplex, with a few, scattered species, and the larger Atriplex clade, which is highly diverse and found around the world.[26] After phylogenetical research, Kadereit et al. (2010) excluded Halimione as a distinct sister genus. The remaining Atriplex species were grouped into several clades.[6]

The following is a cladogram with estimated divergence times for the tribe Atripliceae. To infer the phylogeny, an ITS matrix composed of spacer ITS-1, the 5.8S subunit, and spacer ITS-2 were amplified and sequenced for each specimen. Not all species in the genus Atriplex are presented in the cladogram. Cladogram based on page 7 of Origin and evolution of Atriplex (Amaranthaceaes.l.) in the Americas: Unexpected insights from South American species. (2019).[27] This paper provided new hypothesis suggesting The Americas were colonised by C4 Atriplex from Eurasia or Australia. Further, Atriplex originated in South America, where two lineages underwent in situ diversification and evolved sympatrically. North America was then colonised by Atriplex from South America. Then later one lineage moved back to South America.[27]

Cladogram of estimated divergences within the genus Atriplex

Background colour in cladogram represents the region where a species is endemic.   South America   North America   Australia   Eurasia Brignone et al. (2019) hypothesis for the evolution and movement of Atriplex species globally.[27] Atripliceae Atriplex                           ⊞(15 more species, click to view) ⊟     Atriplex pentandra       Atriplex hystrix       Atriplex clivicola       Atriplex taltalensis       Atriplex vallenarensis     Atriplex peruviana                   Atriplex leuca       Atriplex philippii       Atriplex myriophylla       Atriplex chapinii       Atriplex chizae       Atriplex frigida     Atriplex ameghinoi                   Atriplex monevidensis     Atriplex pamparum           Atriplex serenana         Atriplex leucophylla     Atriplex watsonii             Atriplex acanthocarpa     Atriplex polycarpa           Atriplex canescens     Atriplex phyllostegia         Atriplex obovata     Atriplex powellii             Atriplex parishii         Atriplex hymenelytra     Atriplex parryi         Atriplex lentiformis                     Atriplex undulata       Atriplex patagonica       Atriplex lithophila     Atriplex atacamensis               Atriplex braunii     Atriplex oreophila           Atriplex retusa       Atriplex rusbyi     Atriplex quixadensis           Atriplex sagittifolia     Atriplex vulgatissima               Atriplex cordubensis     Atriplex lampa         Atriplex crenatifolia           Atriplex coquimbana       Atriplex costellata     Atriplex repanda           Atriplex sorianoi     Atriplex spegazzinii             Atriplex boecheri     Atriplex nitrophiloides           Atriplex rotundifolia     Atriplex imbricata                 Atriplex argentina     Atriplex oesteophora       Atriplex asplundii             Atriplex cinerea     Atriplex rhagodioides         Atriplex isatidea     Atriplex nummularia             Atriplex halimus     Atriplex leucoclada                       Atriplex billardierei       Atriplex holocarpa     Atriplex vesicaria         Atriplex spongiosa         Atriplex semibaccata       Atriplex muelleri       Atriplex suberecta     Atriplex eardleyae                 Atriplex centralasiatica     Atriplex siberirica         Atriplex rosea     Atriplex sphaeromorpha               Atriplex dimorphostegia     Atriplex laciniata       Atriplex tatarica         Atriplex moneta     C3 Atriplex clade   sect. Teutliopsis         Atriplex australasica     Atriplex glabriuscula       Atriplex micrantha         Atriplex latifolia     Atriplex oblongifolia             Atriplex calotheca     Atriplex prostrata         Atriplex patula     Atriplex chilensis         sect. Atriplex   Atriplex aucherii     Atriplex hortensis         Atriplex crassifolia             Atriplex lanfrancoi     Atriplex cana       Halimione   Halimione portulacoides     Halimione verrucifera       Archiatriplex clade   Extriplex californica     (13 other taxa)

Selected species not yet investigated phylogenetically:

Excluded species:

• Extriplex:[29]
  • Extriplex californica (Moq.) E.H.Zacharias (Syn. Atriplex californica Moq.)
  • Extriplex joaquinana (A.Nelson) E.H.Zacharias (Syn. Atriplex joaquiniana A.Nelson)
• Halimione Aellen:[6]
  • Halimione pedunculata (L.) Aellen (Syn.: Atriplex pedunculata L.)
  • Halimione portulacoides (L.) Aellen (Syn.: Atriplex portulacoides L.)
  • Halimione verrucifera (M.Bieb.) Aellen (Syn.: Atriplex verrucifera M.Bieb.)
• Stutzia E.H.Zacharias:[29]
  • Stutzia covillei (Standl.) E. H. Zacharias (Syn. Atriplex covillei (Standl.) J. F. Macbr.)
  • Stutzia dioica (Nutt.) E. H. Zacharias (Syn. Atriplex suckleyi (Torrey) Rydberg, Atriplex ovata (Rydb.) Clem. & E. G. Clem.)

• Davidson, Alan (1999): Orach. In: Oxford Companion to Food: 556. ISBN 0-19-211579-0
• Everitt, J.H.; Lonard, R.L.; Little, C.R. (2007). Weeds in South Texas and Northern Mexico. Lubbock: Texas Tech University Press. ISBN 0-89672-614-2