﻿Evans: The genus Plagiochasma 287 



but that it differs in the more crispate margin of the thallus, 

 in the fact that it is wholly convolute when dry, and in its less 

 conspicuous median canal when moist. They likewise quote a 

 specimen collected by Ecklon and Pappe at the Cape of Good 

 Hope, and although they doubtfully refer this specimen to P. 

 rupestre, Lindenberg expresses the opinion that it may be P. 

 mexicanum. Stephani adds no differential characters of impor- 

 tance, stating merely that the epidermal cells are surrounded by. 

 five or six cells with strongly thickened radial walls, that the 

 epidermal cells have trigones, that the ventral scales have a 

 single appendage, narrowly lanceolate and long-attenuate, and 

 that the carpocephalum is excised at the apex with obtuse, 

 recurved-connivent horns. A portion of the type specimen from 

 the Gottsche herbarium showed most of these characters, although 

 some of the epidermal pores were bounded by only four cells 

 (Fig. I, E). The specimen showed nothing, however, to justify 

 the maintenance of P. mexicanum as a valid species. 



Of P. lanigerum authentic material was distributed in Spruce's 

 Hepaticae Spruceanae. In the original description the ventral 

 scales were said to be obliquely triangular and acuminate and the 

 elaters to have four spirals. Stephani adds an account of the 

 epidermal cells, which are said to have trigones, and of the pores, 

 which are said to be surrounded by five cells. He states further 

 that the single appendage of the scales is as long as the basal part, 

 lanceolate in form, and acute, and that the elaters have from two 

 to four spirals. It will be seen at once that there is nothing in 

 either description which would not apply to the variable P. 

 rupestre, and Spruce's specimens amply support this position. 



In addition to the four species just discussed there are several 

 others recognized by Stephani which are evidently very closely 

 related to P. rupestre. Among these are the following: P. 

 dschallamim, P. tenue, P. algericum, P. nepalense, P. chlorocarpum, 

 P. validum, P. caerulescens , P. brasiliense, P. peruvianum, and P. 

 sub planum. It is probable that some of these will prove to be 

 synonymous with P. rupestre, but unfortunately authentic 

 material has not been available for study. A possible exception 

 may be made in the case of P. tenue, which Stephani quotes from 

 three South African regions: the Transvaal, MacLea, Wilms; 



