Riccia cavernosa (Cavernous Crystalwort) is a species of thalloid plant (loosely related to mosses) usually growing on moist soil or mud in damp environments. It was already noted at Jebel Uweinat (in Karkur Murr) by J. Leonard during the 1968 Belgian expedition. It was only observed once, growing on damp mud beside a large guelta in Wadi Wahesh after the 2007 rains. It was unidentified till a recent (2024) observation on the Ouri plain in the Eastern Tibesti some 650km away, in a very similar setting.

Upper Wadi Wahesh (Jebel Uweinat), on damp mud adjacent to large guelta following August 2007 rains.