Phylogeny and taxonomy of the complex thalloid liverwort family cleveaceae cavers
Rubasinghe, Sumudu Chandima Kumari
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Liverworts (Phylum Marchantiophyta) form the earliest diverging lineage of extant land plants and hold a key position in the evolutionary history of land plants. The family Cleveaceae, first defined in 1881 by Leitgeb by its complex thallus anatomy and star-shaped epidermal pores with strongly thickened radial walls, is now included within Marchantiopsida (Complex Thalloid Liverworts). The family is widely distributed in warm temperate to arctic regions throughout the Northern Hemisphere, but very rare in South America and absent from Australia and New Zealand. Since Cleveaceae was described, the number and names of genera and species recognized within the family have changed many times, with three genera currently accepted: Athalamia (12 to 15 species), Sauteria (2 to 5 species) and Peltolepis (1 or 2 species). However, no robust phylogenetic frame work or taxonomic monographs of the family have previously been undertaken and the species diversity within the genera remains uncertain. The study presents the first robust phylogenetic framework for the family, based on three chloroplast genes (psbA, rpoC1 and rps4) and one nuclear ribosomal region (26S) sequenced for 54 ingroup accessions representing a substantial part of the geographic range of the family (except South America) and a large part of its morphological diversity. Samples sequenced include the type species of the three currently accepted genera as well as those of previously synonymised genera; Clevea, Spathysia, Gollaniella and Sauchia. The current circumscription and relationships of the genera were tested using Maximum Parsimony, Bayesian and Likelihood inferences. Cleveaceae was strongly supported as monophyletic with four main lineages resolved within the family, two corresponding to Peltolepis and Sauteria and two composing a polyphyletic Athalamia. The latter is therefore divided into a more narrowly defined Athalamia and a fourth genus, for which Clevea is the earliest published name. Inferred evolutions of twelve morphological characters, that are useful or have been used in classifications of Cleveaceae, were reconstructed using maximum parsimony and maximum likelihood methods. The misleading influence of homoplasy on past morphological classifications and phylogenies is discussed. The study also presents the first worldwide taxonomic revision of Cleveaceae based on around 2300 specimens studied, including all available type specimens. The monographic work is based on morphological and anatomical characters reviewed using dissecting, compound and scanning electron microscopes including both herbarium and fresh material collected on field excursions during the study. Ventral scale morphology, position and aggregation of androecia and shape of receptacle were found to be valuable characters in generic and species delimitation. The traditional definition of genera of Cleveaceae based mainly on two characters (carpocephalum stalk position and anatomy) was rejected. A total of seven species were recognized from 25 formerly described names including one new necessary combination: Clevea hyalina (Sommerf.) Lindb., C. spathysii (Lindenb.) Müll.Frib., C. pusilla (Steph.) Rubasinghe & D.G.Long comb. nov., Athalamia pinguis Falc., Sauteria alpina (Nees) Nees, S. spongiosa (Kashyap) S.Hatt., and Peltolepis quadrata (Saut.) Müll.Frib. Nine excluded and doubtful species are listed along with reasons for their exclusion. Generic and species keys are presented based on vegetative, reproductive and spore morphological characters. For each genus and species, descriptions, illustrations, and distribution maps are given along with ecological, taxonomic and nomenclatural notes.