Atriplex

Atriplex is a plant genus of about 250 species, known by the common names of saltbush and orache. 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 C₃-plants, but most species are C₄-plants, with a characteristic leaf anatomy, known as kranz anatomy.

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.
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 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.
The type species is Atriplex hortensis. The name is derived from Ancient Greek ἀτράφαξυς, "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. 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. 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.

Atriplex lanfrancoi/cana-Clade:
*Atriplex lanfrancoi G. Kadereit et Sukhor. : endemic to Malta and Gozo.
*Atriplex cana C.A. Mey.: from Eastern European Russia to western China.
Atriplex section Atriplex: annual C₃-plants.
*Atriplex aucheri Moq.: in Eastern Europe and West Asia.
* Atriplex hortensis L. - Garden orache, red orach, mountain spinach, French spinach: in Asia, cultivated or naturalized in Europe.
* Atriplex oblongifolia Waldst. & Kit. - Oblong-leaved orache: in Eurasia.
* Atriplex sagittata Borkh. : in Eurasia
Atriplex section Teutliopsis Dumort.: annual C₃-plants.
*Atriplex australasica Moq.
* Atriplex calotheca Fr.: in Northern Europe.
* Atriplex davisii Aellen: from southern Europe to Egypt.
* Atriplex glabriuscula Edmondston - Northeastern saltbush, Babington's orache, smooth orache, Scotland orache, glabrous orache: In central and northern Europe.
* Atriplex gmelinii C.A. Mey. ex Bong. - Gmelin's saltbush: in Asia and North America.
* Atriplex intracontinentalis Sukhor.: from Central Europe to Asia.
* Atriplex laevis C.A. Mey.: in Asia, naturalized in eastern Europe.
* Atriplex latifolia Wahlenb.: in Eurasia.
* Atriplex littoralis L. - Grass-leaved orache: in Eurasia and North Africa.
* Atriplex longipes Drejer - Long-stalked orache: in northern Europe.
* Atriplex micrantha C.A. Mey.: in Asia, naturalized in Europe.
* Atriplex nudicaulis Boguslaw - Baltic saltbush: in Eurasia.
* Atriplex patula L. - Common orache, spreading orache: in Eurasia and North Africa.
* 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 did not reflect the phylogenetical relationships and was rejected by Kadereit et al..
*Atriplex acanthocarpa S. Watson: in North America.
* Atriplex acutibractea Anderson: in Australia.
* Atriplex altaica Sukhor.: in Asia.
* Atriplex angulata Benth.: in Australia.
* Atriplex billardierei Hook. f.: in Australia.
* Atriplex canescens Nutt. - Chamiso, chamiza, four-winged saltbush, grey sagebrush: in North America.
* Atriplex centralasiatica Iljin: in Asia.
* Atriplex cinerea Poir. - Grey saltbush, truganini: in Australia
* Atriplex codonocarpa P.G. Wilson: in Australia.
* Atriplex conduplicata F. Muell.: in Australia.
* Atriplex confertifolia S. Watson - Shadscale : in North America.
* Atriplex cordobensis Gand. & Stuck.: in South America.
* Atriplex deserticola Phil.: in South America.
* Atriplex dimorphostegia Kar. & Kir.: in North Africa.
* Atriplex eardleyae Aellen: in Australia
* Atriplex elachophylla F. Muell.: in Australia.
* Atriplex fissivalvis F. Muell.: in Australia
* Atriplex flabellum Bunge ex Boiss.: in Eurasia.
* Atriplex gardneri D. Dietr. - Gardner's saltbush, moundscale: in North America
* Atriplex glauca L.: in Portugal, Spain and in North Africa.
* Atriplex halimus L. - Mediterranean saltbush, sea orache, shrubby orache: in south Europe, North Africa and southwest Asia.
* Atriplex herzogii Standl.: in North America.
* Atriplex holocarpa F. Muell.: in Australia.
* Atriplex hymenelytra S. Watson - Desert holly: in North America.
* Atriplex hymenotheca Moq.: in Australia.
* Atriplex imbricata D. Dietr.: in South America.
* Atriplex inamoena Aellen: in Eurasia.
* Atriplex intermedia Anderson: in Australia.
* Atriplex isatidea Moq.: in Australia.
* Atriplex laciniata L. - Frosted orache: In western and northern Europe.
* Atriplex lampa Gillies ex Small: in South America.
* Atriplex lehmanniana Bunge: in Eurasia.
* Atriplex lentiformis S. Watson - Quail bush: in North America.
* Atriplex leptocarpa F. Muell.: in Australia.
* Atriplex leucoclada Boiss.: in Eurasia.
* Atriplex leucophylla D. Dietr.: in North America
* Atriplex lindleyi Moq.: in Australia.
* Atriplex moneta Bunge ex Boiss.: in Eurasia.
* Atriplex muelleri Benth.: in Australia.
* Atriplex nessorhina S.W.L. Jacobs: in Australia.
* Atriplex nummularia Lindl. - Old man saltbush, giant saltbush: in Australia.
* Atriplex obovata Moq.: in North America.
* Atriplex pamirica Iljin: in Eurasia.
* Atriplex parishii S. Watson: in North America
* Atriplex parryi S. Watson: in North America
* Atriplex parvifolia Kunth: in South America.
* Atriplex patagonica D. Dietr.: in South America.
* Atriplex phyllostegia S. Watson: in North America.
* Atriplex polycarpa S. Watson - Allscale, desert saltbush, cattle saltbush, cattle spinach: in North America.
* Atriplex powellii S. Watson - Powell's saltbush: in North America.
* Atriplex pseudocampanulata Aellen: in Australia.
* Atriplex quinii F. Muell.: in Australia.
* Atriplex recurva d'Urv.: in Eurasia, endemic to areas around the Aegean.
* Atriplex rhagodioides F. Muell.: in Australia.
* Atriplex rosea L. - Tumbling orache: in Eurasia and North Africa.
* Atriplex rusbyi Britton ex Rusby: in South America.
* Atriplex schugnanica Iljin: in Asia.
* Atriplex semibaccata R. Br. - Australian saltbush, berry saltbush, creeping saltbush: in Australia.
* Atriplex semilunaris Aellen: in Australia.
* Atriplex serenana A. Nelson ex Abrams: in North America
* Atriplex sibirica L.; in Asia, naturalized in Europe.
* Atriplex sphaeromorpha Iljin: in Russia, Ukraine and Caucasus.
* Atriplex spinibractea Anderson: in Australia.
* Atriplex spongiosa F. Muell.: in Australia.
* Atriplex stipitata Benth.: in Australia.
* Atriplex sturtii S.W.L. Jacobs: in Australia.
* Atriplex suberecta I. Verd. - Sprawling saltbush, lagoon saltbush: in Australia.
* Atriplex tatarica Aellen: in Europe, North Africa and Asia.
* Atriplex turbinata Aellen: in Australia.
* Atriplex undulata D. Dietr.: in South America.
* Atriplex velutinella F. Muell.: in Australia.
* Atriplex vesicaria Heward ex Benth. - Bladder saltbush: in Australia.