# Atriplex

Atriplex (/ˈætrɪplɛks/) is a plant genus of about 250 species, known by the common names of saltbush and orache (/ˈɒrɪtʃ, -ətʃ/; also spelled orach). It belongs to the subfamily Chenopodioideae of the family Amaranthaceae s.l.. The genus is quite variable and widely distributed. It includes many desert and seashore plants and halophytes, as well as plants of moist environments. The generic name originated in Latin and was applied by Pliny the Elder to the edible oraches. The name saltbush derives from the fact that the plants retain salt in their leaves; they are able to grow in areas affected by soil salination.

## Description

Species of plants 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 leaves are arranged alternately along the branches, rarely in opposite pairs, either sessile or on a petiole, and are sometimes deciduous. The leaf blade is variably shaped and may be entire, tooth or lobed.
The flowers are borne in leaf axils or on the ends of branches, in spikes or spike-like panicles . The flowers are unisexual, some species monoecious, others dioecious. Male flowers have three to five perianth lobes and three to five stamens. Female flowers are usually lacking a perianth, but are enclosed by two leaf-like bracteoles, have a short style and two stigmas.
After flowering, the bracteoles sometimes enlarge, thicken or become appendaged, enclosing the fruit but without adhering to it.
The chromosome base number is x = 9, except for Atriplex lanfrancoi, which is x=10.
A few Atriplex species are C$_3$-plants, but most species are C$_4$-plants, with a characteristic leaf anatomy, known as kranz anatomy.
* Atriplex elegans
* Atriplex hymenelytra
* Atriplex lentiformis
* Atriplex nummularia
* Atriplex suberecta
* Atriplex patula, female flower with bracteoles and ovule

## Taxonomy

The genus Atriplex was first formally described in 1753 by Carl Linnaeus in Species Plantarum. The genus name was used by Pliny for orach, or mountain spinach (A. hortensis).
The genus evolved in Middle Miocene, the C$_4$-photosynthesis pathway developed about 14.1–10.9 million years ago (mya), when the climate became increasingly dry. The genus diversified rapidly and spread over the continents. The C$_4$ Atriplex colonized North America probably from Eurasia during the Middle/Late Miocene, about 9.8–8.8 mya, and later spread to South America. Australia was colonized twice by two C$_4$ lineages, one from Eurasia or America about 9.8–7.8 mya, and one from Central Asia about 6.3–4.8 mya. The last lineage diversified rapidly, and became the ancestor of most Australian Atriplex species.
The type species (lectotype) is Atriplex hortensis. 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 250-300 species, with new species still being discovered. An example includes Atriplex yeelirrie, formally described in 2015.
Traditional taxonomy of Atripliceae based on morphological features has been controversial. 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. After phylogenetic research, Kadereit et al. (2010) excluded Halimione as a distinct sister genus. The remaining Atriplex species were grouped into several clades.
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 (based on page 7 of). This work suggested that the Americas were colonised by C4 Atriplex from Eurasia or Australia. Furthermore, that in the Americas Atriplex first appeared in South America, where two lineages underwent in situ diversification and evolved sympatrically. North America was then colonised by Atriplex from South America, then one lineage later moved back to South America.
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.
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) :

## Distribution and habitat

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.

## Ecology

Atriplex species are used as food plants by the larvae of some Lepidoptera species; see the list of Lepidoptera which feed on Atriplex. They are also sometimes consumed by camels. 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.

## Uses

The favored species for human consumption is now usually garden orache (A. hortensis), 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. Its seed has been found among apparent evidence of cereal preparation and cooking at Late Iron Age villages in Britain. 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. 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.
A study on A. 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. 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. 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. Old man saltbush (Atriplex nummularia) has also been successfully used to rehabilitate old mining sites in Australia.