Abstract
The genera Anoectangium, Gymnostomum, Hymenostylium, and Molendoa, included in the tribe Pleuroweisieae, are studied in South America. After a thorough revision of both herbarium material and our own recent collections from the area, we recognize eight species among these genera. In Hymenostylium, H. recurvirostrum and H. aurantiacum are accepted, the latter newly reported for the territory. Hymenostylium contextum and H. kunzeanum are placed in the synonymy of H. recurvirostrum and Weissia stillicidiorum and Hydrogonium taylorii of H. aurantiacum. In Gymnostomum, only G. calcareum is recognized in South America. Gymnostomum tenerrimum is considered a synonym of G. calcareum and G. aeruginosum is tentatively excluded from the area. In Molendoa, M. sendtneriana and M. peruviana comb. nov. are recognized. Anoectangium calidum, Molendoa andina, M. subobtusifolia, and Trichostomum glaucoviride are proposed as synonyms of M. sendtneriana and Anoectangium herzogii, A. platyphyllum, A. lechlerianum and Triquetrella cucullata of M. peruviana. Molendoa fuegiana and M. guentheri are excluded from Molendoa and considered synonyms of Didymodon australasiae. In Anoectangium, A. aestivum, A. euchloron and A. stracheyanum are accepted. Anoectangium brachyphyllum and Zygodon tenellus are treated as synonyms of A. euchloron, A. pflanzii of A. aestivum and A. lechlerianum var. laetior and Zygodon linearis of A. stracheyanum. Anoectangium herzogii, A. calidum, and A. lechlerianum var. limbatulum are excluded from Anoectangium. The first is considered conspecific with Molendoa peruviana and the rest with M. sendtneriana. The genus Tuerckheimia represented by T. guatemalensis is excluded from South America. Lectotypes for twenty two names (Anoectangium euchloron f. elata, A. herzogii, A. lechlerianum, A. lechlerianum var. laetior, A. lechlerianum var. limbatulum, A. patagonicum, A. pflanzii, A. sendtnerianum, A. sordidum, A. tenerrimum, Gymnostomum longirostre, G. recurvirostrum, Hymenostylium contextum, H. longopulvinatum, Molendoa fuegiana, Trichostomum glaucoviride, Triquetrella cucullata, Weissia stillicidiorum, W. venezuelensis, Zygodon excelsus, Z. linearis and Z. tenellus) are proposed. A key, descriptions, illustrations and distribution maps are provided for each species.