Taxonomic Revision Of Meteorium (Meteoriaceae, Musci)

Meteorium Dozy & Molk. including 37 species, is a genus of predominantly epiphytic, frequently pendent mosses distributed in tropical and subtropical Asia, Australasia and the Americas. Since it was established, the circumscription of the genus has been in dispute throughout its taxonomic history. The taxonomy of this genus is considered very difficult due to its great variation and inavailability of sporophyte in most occasions. Up to now, there is no comprehensive taxonomic revision on Meteorium. Thus, it is necessary to carry out a world wide taxonomic revision on this genus.The Meteorium are taxonomically revised based on field studies, examination of 2500 speciemens from 22 herbaria, and an extensive review of relevant literatures. During the study, morphological variations shown within and between populations were studied, and the taxonomic significance of the major gross morphological characters were evaluated. Some conclusions are summarized as follows:Meteorium is a natural group, which is characterized by terete foliate plants usually become black with age. Axillary hairs have 1-2 short brown basal cells and 1-4 short hyaline apical cells. The leaves are often auriculate and plicate, with a single costa. Leaf cells are mostly oblong-rhomboidal and unipapillose. The setae are elongate and usually roughened. The peristomes are hypnalean and densely papillose. The calyptra is cucullate and hairy.All species of Meteorium have similar pseudoparaphyllia, cross section of stem and perichaetial leaves, thus, these characters have been confirmed no taxonomic value. Axillary hairs, setae, calyptrae and peristome structure are useful characters for generic classification, but they are nearly identical within Meteorium. However, the plant sizes, shapes of leaves and leaf cells are found to be the most reliable diagnostic characters for the circumscription of species, although sometimes these characters are variable within and between populations of the same species and changed with environmental conditions. The distribution and peristome structure of Meteorium suggested that it is a primitive group in Meteoriaceae, and closely related to Papillaria, Toloxis, Cryptopapillaria and Chrysocladium. The synapomorphic characters for them include terete shoots, similar axillary hairs, a totally papillose exostome outer surface and only slightly serrulate or subentire leaf margin.In this study, nine species are recognized in the present treatment. Among them, four species (M. latifolium, M. teres, M. pseudoteres, M. sinuatum) are restricted to the tropical and subtropical regions of New World, and the other species (M. papillarioides, M. atrovariegatum, M. buchananii, M. elatipapilla, M. polytrichum) occur in eastern and southeastern Asia, and Australasia. Five species are numerated as dubious taxa because of the unavailability of type specimens. Eleven species are excluded from Meteorium. Seventeen species are reduced to synonymies. Four new combinations, Toloxis intricata, Neodicladiella nitens, Neodicladiella deppei and Pseudotrachypus undulifolius are proposed. Three species, M. teres, M. gerale and M. rigidum are lectotypified. The identity of M. polytrichum-M. atrovariegatum-M. subpolytrichum-M. buchananii and M. sinuatum-M.deppei-M. illecebrum was clarified. A key and descriptions of the species are presented. The taxonomic history, synonymies, distribution, and representative specimens are included.