Atriplex

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.^{[6][7][8][9][10]}

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 3-5 perianth lobes and 3-5 stamens. Female flowers are usually lacking a perianth, but are enclosed by 2 leaf-like bracteoles, have a short style and 2 stigmas.^{[6][7][8][9][10]}

After flowering, the bracteoles sometimes enlarge, thicken or become appendaged, enclosing the fruit but without adhering to it.^{[6][7][8][9][10]}

The chromosome base number is x = 9, except for Atriplex lanfrancoi, which is x=10.^[11]

A few Atriplex species are C₃-plants, but most species are C₄-plants, with a characteristic leaf anatomy, known as kranz anatomy.^[11]

•  
  Atriplex elegans
•  
  Atriplex hymenelytra
•  
  Atriplex lentiformis
•  
  Atriplex nummularia
•  
  Atriplex suberecta
•  
  Atriplex patula, female flower with bracteoles and ovule

The genus Atriplex was first formally described in 1753 by Carl Linnaeus in Species Plantarum.^[1][12][13] The genus name was used by Pliny for orach, or mountain spinach (A. hortensis).^[14]

The genus evolved in Middle Miocene, the C₄-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 C₄ 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 C₄ 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.^[11]

The type species (lectotype) is Atriplex hortensis.^[15] 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^[7]-300^[11] species, with new species still being discovered. An example includes Atriplex yeelirrie, formally described in 2015.^[16]

Traditional taxonomy of Atripliceae based on morphological features has been controversial.^[17] 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.^[17] After phylogenetic research, Kadereit et al. (2010) excluded Halimione as a distinct sister genus. The remaining Atriplex species were grouped into several clades.^[11]

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 ^[18]). 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.^[18]

Cladogram of estimated divergences within the genus Atriplex

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)

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.^[11]

Atriplex species are used as food plants by the larvae of some Lepidoptera species; see the list of Lepidoptera which feed on Atriplex.^[20] They are also sometimes consumed by camels.^[21] 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.^[22] 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.^[23][24][25]

The favored species for human consumption is now usually garden orache (A. hortensis),^[26][27][28] 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.^[29] Its seed has been found among apparent evidence of cereal preparation and cooking at Late Iron Age villages in Britain.^[30] 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^[31]). 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.^[32] 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.^[33][32]

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.^[34] 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.^[35] 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.^[36][37] Old man saltbush (Atriplex nummularia) has also been successfully used to rehabilitate old mining sites around Lightning Ridge (Australia).

• Barbara Hulme, producer of Atriplex hybrids

• 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