Cololejeunea linopteriodes H. Rob. is described in detail with special reference to its exceptional flattened stem structure and reduced lobule, which seem to be adaptations to the growth form of a closely appressed epiphyll. Differences from the similar C. sigmoidea Ast & Tixier and other related species are discussed. Resumen. Cololejeunea linopteroides H. Rob. se describe detalladamente, con especial referencia a caracteristicas como el Idbulo reducido y la estructura plana del tallo, las cuales parecen constituir adaptaciones a su tipo de crecimiento como epifilos muy adheridos al sustrato. Se discute las diferencias con C. sigmoidea Ast & Tixier y otras especies muy relacionadas. In the frame of an ecological and taxonomic investigation of epiphyllous Lejeuneaceae in tropical rainforests of Costa Rica we found a particular species of the genus Cololejeunea. It is similar to C. sigmoidea Ast & Tixier (Jovet-Ast & Tixier 1962) in the extremely reduced lobule consisting of only one cell, rounded leaf shape, sigmoid leaf cells, and stem closely appressed to the substrate. The main difference we found was in stem structure, rounded in C. sigmoidea, but especially flattened in our species. Furthermore, C. sigmoidea was only known from Asia (Mizutani 1978). The Costa Rican species was considered as new to science (as C. gradsteinii nom. inval. by Luicking & Morales in LUcking 1995), but then we discovered C. linopteroides H. Rob. (Robinson 1964), described from Costa Rica and after careful examination of the type it was clear that our new species is identical to that species. Cololejeunea linopteroides and C. sigmoidea are closely related, but different species with C. sigmoidea occurring in Asia and C. linopteroides in the Neotropics. Because of the inconspicuous differences, C. linopteroides might have been frequently confused with C. sigmoidea in the past, and we are sure that further examination of herbarium material from the Neotropics and identified as C. sigmoidea will turn out to be C. linopteroides. In the original description of C. linopteroides (Robinson 1964), nothing was mentioned about the flattened stem or the similarity to C. sigmoidea. It is also incomplete in characterizing the lobule and the female branches. Therefore we describe the species here in detail, and its particular morphological structures i.e., the flattened stem structure and the reduced lobule are discussed in regard to similar species as well as to environmental conditions. COLOLEJEUNEA LINOPTEROIDES H. Rob., THE BRYOLOGIST 67: 457. 1964. TYPE: COSTA RICA. ALAJUELA PROVINCE. San Antonio de Zarcero, Smith 48/312 (us!). Plants mostly epiphyllous, olive to brown when dry. Shoots with leaves 0.7-1.1 mm wide (Fig. lA). Stems brown, 85-105 sm wide, strongly flattened with four large, dorsal, cortical cell rows, forming a plane; in well developed plants one medullary and three small ventral cortical cell rows present (Fig. iB); at rhizoid disks ventral cortical cells merged into rhizoids, thus apparently reduced in transverse section (Fig. IC). Lateral leaves slightly imbricate, oval, at base angulate, spreading, 0.3-0.5 mm long 0.25-0.45 mm broad, margin entire, closely appressed to substrate; from dorsal view lateral leaves only partly covering stem. Lobules reduced (Fig. iD), consisting of one cell with large, ligulate, hyaline papilla. Below the lobule at leaf base two large, inflated, and thick-walled cells present. Leaf cells smooth, sigmoidal in form especially at margin, cells in lower middle and at base elongate-quadrate; marginal cells 5-10 x 15-30 pxm, at the base 20-37 X 35-65 sm. Cell walls thin, without trigones. Oil bodies homogenous (sometimes slightly segmented but may be an effect of dissolution), about 10-15 per cell, botryoidal to elongate 2-3 x 3.0-5.5 pm (Fig. 1G). Gemmae developing on dorsal surface of leaves (Fig. 1E), rounded to slightly triangular, consisting of about 18-20 cells when mature, 50-70 pLm 0007-2745/99/437-441$0.65/0 This content downloaded from 157.55.39.145 on Wed, 20 Jul 2016 04:10:17 UTC All use subject to http://about.jstor.org/terms 438 THE BRYOLOGIST [VOL. 102 E 6Z11 : A~~ ". .I: -{?