Abstract:
Although the family Polytrichaceae contains the largest and structurally most complex of all mosses, a number of distantly related lineages share a relatively reduced gametophytic morphology and have historically been conflated under polyphyletic genera, most notably Oligotrichum s.l. Based on new and newly identified collections, phylogenetic analysis of nucleotide data, scanning electron microscopy and relaxed-clock divergence time estimation, we recognise O. glaciale and O. cavallii under the new genus Delongia, which is more closely related to Psilopilum, Atrichum and Steereobryon than to Oligotrichum. The two species are mutually highly distinct in both morphological and molecular characters, with D. glacialis occurring across the Himalaya from Pakistan to Yunnan and D. cavallii found in the East African Rift Mountains and on the island of Reunion. Divergence time estimation suggests that the lineages represented by the extant species diverged from each other around the Oligocene-Miocene boundary (~23 Ma), contemporaneous with the origins of the East African Rift system and ongoing uplift of the Qinghai-Tibetan Plateau, while Delongia most likely shares a common ancestor in the Eocene (56—34 Ma) either with the arctic-subarctic genus Psilopilum or with Atrichum and Steereobryon.
