Arthrocaulon is a genus of halophytic (salt-tolerant) flowering plants in the family Amaranthaceae (sometimes placed in Chenopodiaceae), order Caryophyllales. It belongs to subfamily Salicornioideae and was established in 2017 by Piirainen & G. Kadereit, comprising species formerly classified under Arthrocnemum. The type species is Arthrocaulon macrostachyum.
Plants of this genus are much-branched subshrubs that form clumps up to a metre in height. They have horizontal woody stems that may root at the nodes, branching into erect, jointed, succulent green stems. The leaves are reduced to small, scale-like structures that clasp the stem with their tips free. The minute flowers are arranged in groups of three within terminal, cylindrical spikes; the perianth is conical with three teeth. The hermaphrodite flowers are wind-pollinated, and the fruit is small with a membranous pericarp containing a single seed.
The genus currently includes three recognised species: A. macrostachyum (the type), A. meridionalis, and A. franzii. Plants are adapted to saline environments, accumulating high concentrations of sodium and chlorine ions, and are found in coastal and inland salt marshes, alkali flats, and other saline-soil habitats.
Distribution
The genus Arthrocaulon is native to Macaronesia, the Mediterranean region, the Arabian Peninsula, and extends to Senegal and Angola in West Africa. The type species, A. macrostachyum, is found along the coasts of the Mediterranean Sea and Red Sea, ranging into the Jordan Valley, and eastwards through the Middle East into Iran and Pakistan, where it grows in coastal salt marshes and muddy swamps immediately inland from mangrove stands.
Ecology
Arthrocaulon species are halophytes — plants adapted to life in saline environments. They grow in coastal and inland salt marshes, alkali flats, and other habitats with high soil salinity. A. macrostachyum germinates best at 200–400 mM NaCl and can germinate at concentrations exceeding 800 mM NaCl. Approximately 60% of its dry mass is ash, largely from accumulated sodium and chlorine ions. The plants are metal-tolerant: they can survive cadmium concentrations toxic to most plants and bioaccumulate the metal, offering potential for phytoremediation of contaminated sites. They also play a pioneering role in the recovery of oil-contaminated coastal soils in the Persian Gulf region.
Taxonomy Notes
The genus Arthrocaulon was established in 2017 by Piirainen & G. Kadereit to accommodate species previously placed in Arthrocnemum, within subfamily Salicornioideae. Family placement is disputed: Wikipedia and APG classification treat the genus within Amaranthaceae, while GBIF retains it under Chenopodiaceae, reflecting the traditional split of these two families.
