Genus of plants
Pseudolithos is a genus of succulent flowering plants of the family Apocynaceae, indigenous to arid areas of Somalia, Yemen and Oman. 
Description and naming.
The plants were first described as a genus in 1965; the name "Pseudo-lithos" means "false-stone" and refers to their pebble-like appearance. It was originally proposed as "Lithocaulon" earlier in 1956, but this name was already in use for a genus of fossil algae. All species in this genus are highly succulent, small in size, and exhibit tessellation on their stems' surface. Their small flowers appear on the spherical body's surface.
Taxonomy.
Phylogenetic studies have shown the genus to be monophyletic, and most closely related to the widespread "Caralluma" stapeliads of North Africa. Marginally more distantly related is a sister branch comprising the genera "Echidnopsis" and "Rhytidocaulon".
References.
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