Abstract
Supposed syntype specimens of Frullania mexicana comprise two morphologically distinct species. One is the authentic F. mexicana, consistent with its original description in Synopsis Hepaticarum. A lectotype is designated for that species based on a specimen in C.G. Nees von Esenbeck’s herbarium, now in STR. The other was listed by F. Stephani as ‘F. mexicana’ in Species Hepaticarum, but is not that species. Rather, it is described here as new based on a specimen deposited in Stephani’s herbarium, now in G. Frullania clarkii sp. nov. differs from F. mexicana in having involute versus more or less flat dorsal lobes; a ligulate, instead of triangular to narrowly triangular proximal portion of the lobule; broadly ovate underleaves with repand margins versus obovate underleaves with plane margins; and 4-keeled versus 8–10 keeled perianth. Its closest morphological affinities are with F. laxiflora and F. planifolia.