﻿288 Evans: The genus Plagiochasma 



Usambara, Hoist; and Angola, Welwitsch. In the Underwood 

 herbarium there is a specimen from A. Rehmann's Hepaticae 

 austro-africanae, No. 32, collected by MacLea at Miiller's Farm 

 in the Transvaal and labeled "Plagiochasma muricata Steph." 

 This species was never published but the specimen probably 

 represents P. tenue, because no other species of MacLea's Trans- 

 vaal collection is quoted. Since MacLea's specimen is cited first 

 ^ by Stephani it is even probable that the plant in the Underwood 

 herbarium is part of the type material. The distinguishing 

 characters of P. tenue are said to be the following: the dioicous 

 inflorescence (androecia unknown), the very minute epidermal 

 pores surrounded by four cells, the triangular ventral scales bifid 

 two-thirds with parallel, contiguous, narrowly triangular divisions 

 (the latter of course being really the appendages), and the strongly 

 convex carpocephala. MacLea's specimen shows most of these 

 characters except that the carpocephala are distinctly concave. 

 The other characters, moreover, are subject to variation, the pores 

 being sometimes surrounded by five cells and the ventral scales 

 sometimes having a single appendage and sometimes two more 

 or less divergent appendages. In other words the specimen 

 agrees in all essential respects with P. rupestre. Whether the 

 other specimens quoted by Stephani represent P. rupestre cannot 

 of course be decided, but the probability is that they do. 



If P. rupestre is accepted in the broad sense of the present 

 paper its geographical distribution becomes very extensive. It is 

 not, however, unique in this respect among the Marchantiaceae. 

 Both Targionia hypophylla and Rehoulia hemisphaerica have a 

 similar and even wider range. Probably if P. rupestre extended 

 as far north in Europe as these other two species, it would long ago 

 have been thoroughly known to European writers, and the con- 

 fusion regarding its synonymy would already have been dispelled. 



2. Plagiochasma crenulatum Gottsche 

 Plagiochasma crenulatum Gottsche, Mex. Leverm. 266. 1863. 

 Aytonia crenulata Underw. Bot. Gaz. 20: 66. 1895. 



Thallus pale green above but not glaucous, with a narrow purple 

 border, plane or broadly canaliculate, strap-shaped, sparingly fork- 

 'ith adventive branches, rarely (if ever) innovat- 



