TORTULA MUCRONIFERA (POTTIACEAE, MUSCI), A NEW XEROPHYTIC SPECIES OF THE ARABIAN PENINSULA AND JORDAN - STUDIES IN ARABIAN BRYOPHYTES-18

A new xerophytic pottiaceous species, Tortula mucronifera is described from the Arabian Peninsula and Jordan. Because of its mucronate leave s, the ventrally thickened costa by a row of 3-4 elongated, swollen, p apillose cells, 2-3(-4) guide cells and the dorsal stereid band, 3-4 c ells thick, it belongs to the section Crassinerves of the genus Tortul a. In habit it resembles a member of the genus Pottia, while the peris tome (32 filiform, not spirally twisted teeth on a short basal membran e) shows affinities to the genus Desmatodon s.l. It differs from Desma todon s.str. by its peristome teeth, rising directly from the very sho rt basal membrane. From Tortula atrovirens, T. brevissima and T. revol vens var. obtusata it can be easily distinguished by the ovate-ellipti c to spathulate leaves and the strong mucro. Tortula mucronifera is ad apted to very dry regions of the Arabian Peninsula with less than 150 mm rainfall per year.