Weissiodicranum insularum Reese gen. et sp. nov. is described on six specimens from the Galapagos, Jamaica, and Puerto Rico. The new species is superficially similar to Weissia breutelii C.M., with which it is sympatric in part, but is distinct in having differentiated alar cells and enlarged cells on the dorsal surface of the costa. Thefamilial placement is uncertain due to lack ofsporophytes but the new genus is tentatively assigned to the Pottiaceae. A lectotype is designated for Weissia breutelii C.M. The specimens described below were discovered during a study of herbarium material from the neotropics previously classified as Hymenostomum or Weissia. Close examination of these plants showed that although they superficially resemble W. breutelii C.M. they differ notably in having conspicuously enlarged alar cells, a feature not known in Weissia. The combination of involute leaf margins and inflated alar cells is unique and these plants are here described as a new species in a new genus. WEISSIODICRANUM Reese gen. nov. Habitu Weissio simile sed cellulae omnes foliorum plus minusve epapillosae et in regione alari inflatae satis absimile. TYPE: The type of Weissiodicranum insularum Reese. WEISSIODICRANUM INSULARUM Reese sp. nov. (FIG. 1-4) Plantae parvae nitidae, folia subulata, margine valde involuta, Weissio breutelii simillimae, sed cellulae alares subinflatae, pariete fuscato; fructus ignotus. Plants glossy, darkto yellowish-green, to 1 cm tall but mostly shorter, rhizoids reddish-brown, scanty, only at bases of stems; stems brown below, simple, or repeatedly forked distally when bearing perichaetia, in section showing 1-2 outer layers of small thick-walled cells with dark-brown walls surrounding 2-3 layers of larger thinner-walled cells with yellowish walls, and well-defined central strand of cells with very thin walls; leaves tightly crispatecurled when dry, spreading-ascending and flexuous when wet, mostly 3-3.5 mm long, narrowly subulate above, with a broader yellowish, often decurrent, clasping base; leaf margins entire, undifferentiated, narrowly involute from just above expanded portion of leaf base to apex; median leaf cells thickwalled, square to rectangular, commonly transversely elongate, averaging 7-7.8 x 5.5-6.5 Am, smooth dorsally, moderately bulging ventrally; cells of leaf base yellowish, rectangular, weakly chlorophyllose except along costa, with smooth walls, 68 alar cells in a single row along insertion inflated and with dark walls; costa strong, smooth dorsally, with bulging to bulging-papillose cells ventrally, excurrent as a sharp yellowish multicellular mucro, in section showing a median row of guide cells and dorsal and ventral tracts of stereid cells, outer cells enlarged and chlorophyllose dorsally and ventrally; perichaetia multiple, produced terminally on stem tips but repeatedly overtopped and appearing lateral, with 6-8 archegonia, leaves scarcely differentiated but commonly lacking inflated alar cells; perigonia and sporophytes unknown. TYPE: PUERTO RICO. DISTR. ARECIBO: Reserva Forestal Cambalache, just E of Garrochales, 500 ft., mesic forest over limestone, on thin soil over limestone, 4 Nov 1990, Buck 18289 (holotype, NY; isotypes, BUF, GA, LAF, MO). PARATYPES: ECUADOR. GALAPAGOS: Isla San Cristobal, between Tres Palos and Fresh Water Beach, 150-250 m, very common on soil, 22 May 1977, Gradstein & Weber M-133 (LAF, U); Isla Santa Cruz, vicinity of Academy Bay, below Bella Vista, on shallow soil, 30 Jan 1964, Weber B13007 (COLO, NY). JAMAICA. MANCHESTER PARISH: Marshall's Pen, 3 mi. WNW of Mandeville, 2300 ft., 18?05'N, 77?32'W, dry secondary forest over rough limestone, on soil, 14 Apr 1981, Buck 5777 (NY). PUERTO RICO. DISTR. ARECIBO: Reserva Forestal Cambalache, just E of Garrochales, ca. 175 m, mesic forest on limestone in haystack hills, on limestone, 11 Jun 1988, Buck 16167 (NY, LAF); near Santurce, on the ground, 15 May 1899, Heller & Heller 835 (NY). The new species is known only from the six specimens cited above. The plants show remarkable constancy in all their characters across the wide geo0007-2745/91/308-310$0.45/0 This content downloaded from 207.46.13.40 on Wed, 30 Mar 2016 05:44:59 UTC All use subject to http://about.jstor.org/terms 1991] REESE & BUCK: WEISSIODICRANUM INSULARUM GEN. ET SP. NOV. 309