Caroxylon is a genus of shrubby flowering plants in the family Amaranthaceae (order Caryophyllales). The genus was originally described by Thunberg in 1782 and was historically treated as a section within the larger genus Salsola, but has been resurrected as a distinct genus in modern taxonomic treatments based on molecular phylogenetic evidence. Species are dwarf shrubs to shrubs (rarely small trees), typically found in arid and semi-arid regions of the Old World.
Plants are characterized by alternate, often succulent leaves that are terete or semiterete and linear, occasionally with a spiny apex. The small, usually bisexual flowers are sessile, borne solitary or in clusters within simple or paniculate spikes, and are protandrous. Each flower has five tepals that develop distinctive wing-like outgrowths in fruit, functioning as an anemophilous (wind-dispersed) diaspore. Five stamens with appendaged anthers are present, inserted on a glandular interstaminal disc. The fruit is a utricle enclosed by the persistent, winged fruiting perianth.
The genus includes well over 100 species, with notable members including Caroxylon imbricatum (formerly Salsola imbricata), C. aphyllum, C. vermiculatum, and C. dendroides. The greatest species diversity is in southern Africa, with significant representation across North Africa, the Middle East, and Central Asia.
Distribution
Caroxylon is distributed across drier areas of the Old World, spanning southern Africa, Madagascar, northern Africa, the Mediterranean islands of Europe, the Canary Islands, Socotra, Ukraine, Russia, western Asia, Central Asia, India, and western and northern China to Mongolia. The genus is centered in the Old World desert belt, with the highest species diversity occurring in southern Africa. A few species extend along seashores and into disturbed, semi-humid habitats.
Ecology
Caroxylon species are predominantly plants of arid and semi-arid environments, occupying desert and semi-desert scrub, dry shrublands, and saline or alkaline soils across the Old World. They are well-adapted to drought and high temperatures, with succulent leaves that reduce water loss. A minority of species occur along seashores, on ruderal sites, or in naturally disturbed ground, occasionally penetrating into adjacent semi-humid areas. The winged fruiting perianth facilitates wind dispersal (anemochory) across open landscapes.
Taxonomy
Caroxylon was originally described by Carl Peter Thunberg in 1782 (Nov. gen. 2: 37). It was later subsumed into the broad genus Salsola (Chenopodiaceae, now placed in Amaranthaceae) and treated as a section within that genus for much of the 19th and 20th centuries. Multiple generic synonyms have been applied to elements of what is now recognized as Caroxylon, including Salsolaria Moq. (1840), Hypocylyx Wol. (1886), Darniella Maire & Weiller (1939), Climacoptera Botsch. (1956), Nitrosalsola Tzvelev (1993), and Xylosalsola Tzvelev (1993).
Molecular phylogenetic studies in the early 21st century demonstrated that the traditional Salsola was polyphyletic, leading to the resurrection of Caroxylon as a distinct genus within the tribe Salsoleae (subfamily Salsoloideae, family Amaranthaceae). Many species previously placed in Salsola have been transferred to Caroxylon, resulting in a genus of over 100 accepted species as of 2024.
