Family: Amaranthaceae |
Plants glabrous, halophytic, rhizomatous shrubs, often forming mats. Stems flesh and apparently articulated when young, later woody and not articulate. Leaves decussate, fused with each other at the base, decurrent and adnate to the stems, forming fleshy segments; blades forming a narrow time at the top of each segment, basal parts fleshy, margins narrowly scarious, tips broadly acture to obtuse, each leaf pair separated from the next by a furrow that encircles the stems. Inflorescences spikelike sessile thyrses, apparently articulated, terminal on the main stems and some branches, each fertile segment composed of 2 opposite cymes of 3 more or less erect flowers arranged in a row in the axil of a bract., central flowers slight larger than the other two, all flowers more or less tubular in outline. Flowers usually bisexual, sometimes the lateral flowers unisexual; perianths of central flowers oconical or obraconially trapezoid, those of the lateral flowers more tubular; tepals 3-4, united except at the tips, persistent in fruit; stamens 1-2; stigmas 2. Fruits utricle-like, saccate, saccate, almost symmetrical; pericarps membranous; seds vertical, ellipsoid, not enclosed in the pericaprs; test shiny, black, crustaceous, tuberculate to minutely papillose at the embryo-bearing seed margin, areolate at tjhe faces, with long elongated areolae; embryos L-shapeds, perisperm abundant. Arthrocaulon includes two species. One of them Arthrocaulon macrostachyum, grows in Somaliland and Somalia. I. Friis & M.G. Gilbert. As Arthrocenumum. Flora of Somalia 1: 131 Plants perennial herbs or subshrubs, glabrous throughout. Stems woody when old, jointed and apparently leafless when young, made of of cylindrical segments formed from almost completely fused pairs of opposite leaves which cover each internode with their free tips forming a short cupule with tips on oppsite sides; leaf and bark tissue with sclereids. Inflorescences terminal, spikelike, with cymes of 3-flowers sessile in axils of a pair of opposite bracts. Flowers of equal height, central flowers bisexual, lateral flowers sometimes male; perianth segments completely fused, obscurely 3-4-lobed, with truncate tops; stamens 1(-2), adaxial. Fruits surrounded by spongy perianth, pericarp hyaline or woody; seeds ovate to orbicular, testa custaceous, granular or smooth; embryos straight or U-shaped, endosperm present. The Flora of Somalia account states that Arthocnemum included 2 species, one of which grows in Somaliland and Somalia, the other in California. The species in Somaliland and Somalia is now included in Arthrocaulon (Piiraine et al. 2017) which is treated as a genus of 2 species, neither or which grows in California. The only clear difference between the description in the Flora of Somalia and that provided by Piiraine et al. is in the shape of the embryo. The only species of Arthrocaulon to grow in Somaliland and Somalia is Arthrocaulon macrostachyum. It is present in both countries. Piirainen,M., O.Liebisch, & G.Kadereit (2017) Phylogeny, biogeography, systematics and taxonomy of Salicornioideae (Amaranthaceae/Chenopodiaceae) – A cosmopolitan, highly specialized hygrohalophyte lineage dating back to the Oligocene. Taxon 66: 109-132. DOI https://doi.org/10.12705/661.6 Global distribution of Arthrocnemum. Note: GBIF records include introduced and cultivated plants. Consequently, the distribution shown often differs from statements about a taxon's native distribution.
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