294 



BRYOPHYTA OF SOUTHERN RHODESIA. 



BY 



T. R. Sim, D.Sc, F.L.S., and H. N. Dixon, M.A., F.L.S. 



Bead July 15, 1921. 



The present paper dealing with the Brycphyta, mainly of 

 Southern Rhodesia, consists of three portions. The introductory 

 section has been prepared by the first-named author, who also deals 

 with the second section on the Hepaticae, while the third section, 

 relating to the Mosses, has been the work of the second-named 

 author. 



Contexts. P & g e 



1. Conditions affecting distribution 294 



2. Hepaticae 296 



3. Mosses 



From Southern Rhodesia 298 



From Portuguese Gaza Land 331 



I.— CONDITIONS AFFECTING THE DISTRIBUTION OF 

 BRYOPHYTA IN RHODESIA. 



BY 



T. R. Sim, D.Sc, F.L.S. 



Such a huge area as Rhodesia would naturally be expected 

 to have a very considerable moss flora, but so far very few species 

 have been recorded. This is partly through its being as yet 

 bryologically unexplored, bat much more completely through its 

 natural conditions. 



The greater part of Rhodesia is in a general way a flat 

 plateau, 3,000 to 5,000 feet altitude, with a few higher granite 

 ridges scattered in. These conditions favour mist-laden clouds pass- 

 ing overhead, without depositing rain or dew, and consequently 

 the general atmospheric condition is one of aridity, which becomes 

 more and more pronounced westward, where Rhodesia meets the 

 still drier Kalahari desert in Bechuanaland, and where the aridity 

 may have increased considerably during recent decades through 

 the drying up of the lake district whence its clouds mostly come. 



It is the presence of that dry region, and of the flat arid 

 surface, which leads to rains being few but torrential; mists 

 usually absent, vegetation a scattered and xerophytic scrub inter- 

 mixed with grass, while Bryophyta are almost absent from all 

 western localities, and of comparatively few species even in the 

 east, though what species there are become much more abundant 

 eastward, especially on the escarpment and on the hills and valleys 

 overlooking the sea slope and the Limpopo and Zambesi valleys, 

 where mists are frequent and conditions much more congenial. 



During my recent tour I found mosses almost, absent west of 

 32° East, except at the Falls of the Zambesi, but from there 



