Orthostichella Müll. Hal. is a genus of nine species (O. capillicaulis, O. hexasticha, O. longinervis, O. muelleri, O. pachygastrella, O. pandurifolia, O. rigida, O. versicolor and O. welwitschii) found only in tropical and subtropical regions of the New World and Africa. One species (O. hexasticha) is restricted to the Caribbean, one (O. pachygastrella) is found only in the continental regions of the New World, two (O. capillicaulis and O. pandurifolia) are restricted to continental Africa, and one (O. longinervis) is found only in Madagascar and the Mascarene Islands. The other species occur in both Africa and the New World. Orthostichella is predominantly epiphytic and often grows in dense, pendent masses. It has a complex morphology with creeping primary stems or stolons, and erect or pendent, stipitate or evenly foliose secondary stems that are irregularly branched. It lacks a stem central strand and its axillary hairs are usually reddish throughout. Its branches often end in filiform attenuations or stolons. The stolons, stems and branches can abruptly transform from one structure to another, or they can seamlessly intergrade one into another. The leaves are often spirally ranked, they have elongate, smooth, firm-walled leaf cells and weakly developed alar cells. The costae in Orthostichella are wildly variable. In some species most leaves are ecostate, however, some leaves can be found with double or single costae. In other species most leaves have a single or double costa, but ecostate leaves can also be found. In one species (O. longinervis) the leaves always have long, single, subpercurrent costae. Orthostichella has elongate-flexuose, roughened setae, ovoid to short-cylindrical capsules, long-rostrate opercula and mostly hairy, cucullate calyptrae. The Orthostichella peristome is diplolepideous and reduced. Exostomes and endostomes are yellowish white and nearly the same length. The more or less linear exostome teeth are lightly, horizontally striate on the dorsal (outer) surface at base. The endostome has a low basal membrane with filamentous, narrowly perforate segments and cilia are usually absent. Orthostichella appears best placed in the Neckeraceae by virtue of its neckeroid peristome, creeping stolons, stipitate stems with differentiated stipe leaves, foliose pseudoparaphyllia and leaves with weakly developed alar cells. Within the Neckeraceae Orthostichella seems best placed near Porotrichum, but the genus appears isolated by virtue of its non-complanate leaves that are often arranged in spiral rows. Additional new combinations include: Orthostichidium quadrangulare (Schwägr.) n. comb., Orthostichidium pentastichum (Brid.) n. comb. and Hildebrantiella phleoides (Desv. ex Brid.) n. comb.
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Vol. 110 • No. 1