Atriplex (/ˈætrɪplɛks/[2]) is a plant genus of about 250 species, known by the common names of saltbush and orache (/ˈɒrɪtʃ,-ətʃ/;[3][4] also spelled orach). It belongs to the subfamilyChenopodioideae of the familyAmaranthaceaes.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.[5] 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.[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]
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 C4Atriplex 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]
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
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.[18]
Atriplex praecox Hülph. – Early orache: in northern Europe.
Atriplex prostrata Moq. – Spear-leaved orache, thin-leaved orache, triangle orache, fat hen: in Eurasia and North Africa.
C4-Atriplex-Clade: containing the majority of species. The traditional classification into sections (sect. Obione, sect. Pterochiton, sect. Psammophila, sect. Sclerocalymma, sect. Stylosa) did not reflect the phylogenetical relationships and was rejected by Kadereit et al. (2010).[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]
Uses
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).
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.
^ abcStanley L. Welsh: Atriplex - online, In: Flora of North America Editorial Committee (ed.): Flora of North America North of Mexico, Volume 4: Magnoliophyta: Caryophyllidae, part 1., Oxford University Press, New York. 2003, ISBN0-19-517389-9.
^ abcdGelin Zhu, Sergei L. Mosyakin & Steven E. Clemants: Chenopodiaceae: Atriplex - online, In: Wu Zhengyi, Peter H. Raven, Deyuan Hong (ed.): Flora of China, Volume 5: Ulmaceae through Basellaceae., Science Press und Missouri Botanical Garden Press, Beijing und St. Louis, 2003, ISBN1-930723-27-X.
^ abcWalsh, Neville G. "Atriples". Royal Botanic Gardens Victoria. Retrieved 16 July 2022.
^ abcJacobs, Surrey W.L. "Atriplex". Royal Botanic Garden Sydney. Retrieved 16 July 2022.
^ abcdefgGudrun Kadereit, Evgeny V. Mavrodiev, Elizabeth H. Zacharias & Alexander P. Sukhorukov: Molecular phylogeny of Atripliceae (Chenopodioideae, Chenopodiaceae): Implications for systematics, biogeography, flower and fruit evolution, and the origin of C4 Photosynthesis. - American Journal of Botany 97(10): 1664-1687, 2010.
^Linnaeus, Carl (1753). Species Plantarum. Vol. 2. pp. 1052–1053. Retrieved 19 June 2022.
^Carl Linnaeus (1753), "Atriplex", Species Plantarum, vol. 2, Lars Salvius/Biodiversity Heritage Library, pp. 1052–1054, retrieved 19 May 2015
^Sharr, Francis Aubi; George, Alex (2019). Western Australian Plant Names and Their Meanings (3rd ed.). Kardinya, WA: Four Gables Press. p. 61. ISBN9780958034180.
^ abcBrignone, Nicolás F.; Pozner, Raúl E.; Denham, Silvia S. (October 2019). "Origin and evolution of Atriplex (Amaranthaceae s.l.) in the Americas: Unexpected insights from South American species". Taxon. 68 (5): 1027. doi:10.1002/tax.12133. S2CID214371753.
^Tasmanian name, also transcribed trucanini, trucaninny, trugannini, trugernanna, etc. The plant was the namesake for Truganini, among the last of her people.
^ abPearce, Kelly & Jacob, Robin (2004): Saltbush lifts sheep meat vitamin content. Farming Ahead153(October): 63. PDF fulltextArchived July 23, 2005, at the Wayback Machine
^Norman, Hayley C.; Freind, Colby; Masters, David G.; Rintoul, Allan J.; Dynes, Robyn A. & Williams, Ian H. (2004): Variation within and between two saltbush species in plant composition and subsequent selection by sheep. Aust. J. Agr. Res.55(9): 999–1007. doi:10.1071/AR04031 (HTML abstract)
^Wilson, A.D.; Harrington, G.N. (1980). "Nutritive value of Australian browse plants". International Livestock Centre for Africa. Addis Ababa: 291.
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