Taxonomy and phylogeny of the liverwort genus Mannia (Aytoniaceae, Marchantiales)

Abstract

The genus Mannia (Aytoniaceae, Marchantiales) was first described by Opiz in 1829 and it is still not clear how many species it comprises worldwide. The generic and subgeneric division of Mannia has long been confused and several attempts have been made to subdivide it into smaller genera. Morphologically it is typically characterised by a small, rather narrow thallus, cup-shaped involucres and the lack of a pseudoperianth. It includes both xeromorphic and mesomorphic species, which are all drought- tolerant. Mannia occurs almost exclusively in the northern hemisphere with exceptions in Africa and South America. It is found on rock, rocky soil or rock crevices in arctic - alpine and Mediterranean climates.

A worldwide revision of the genus has not been previously attempted, and earlier treatments focused on thallus morphology and limited geographic regions.

This study comprises the first worldwide revision of Mannia and about 1600 specimens were studied, including all available type specimens, from both dried and fresh material collected on several field trips. The monographic work is based on reviewed morphological and anatomical characters using dissecting, compound and scanning electron microscopy. Surface ornamentation of spores has been studied and with their relatively large spores reaching up to about 90 μm diameter, the species within Mannia show striking spore ornamentation patterns, which are found to be species -specific and have proved to be a very valuable tool in identification and synonymy. Most spore characters are constant with only size showing large variations though this can nevertheless be diagnostic. The species status of M. sibirica is confirmed and its close relationship to M califo-rnica is contrary to former assumptions.

A total of seven species are recognised from 22 formerly described names: (1) M. androgyna (L. ) A. Evans, (2) Mannia sihirica (Milll. Frib) Frye & L. Clark, (3) Mannia califarnica (Gottsche ex Underw. ) L. C. Wheeler, (4) Mannia fragrans (Balbis) Frye & L. Clark, (5) newly described Mannia asiatica Schill & D. G. Long, (6) Mannia triandra (Scop. ) Grolle and (7) Mannia pilosa (Hornem. ) Frye & L. Clark. Eleven excluded or doubtful taxa are listed. Vegetative, generative and spore keys have been developed and for each species descriptions, illustrations and distribution maps are given along with ecological, taxonomic and nomenclatural notes.

Most species have a wide distribution range except for M androgyna, which is restricted to areas with a Mediterranean climate and M asiatica, which only occurs in high mountains of the Himalayas along the fringes of the Tibetan plateau. The distribution of M californica is extended from North America into Europe, Asia, India and Africa. M fragrans is reported new to India and M californica new to Austria, although the latter specimen shows some atypical morphological features. Some formerly assumed local endemic species are shown to be conspecific with more widespread taxa.

A parsimony analysis based on morphological characters including all Mannia species and 16 other taxa is inconclusive. A study of character evolution showed that homoplasious characters were a common feature in Mannia and related genera.

Reconstructions of phylogenetic relationships using chloroplast trnL-F and nuclear ribosomal LSU were based on 35 samples. Only five out of the seven accepted Mannia species could be included in the molecular study. Some species are represented multiple times but from different countries. Targionia bypopbylla and Athalamia byalina were used as outgroup taxa.

Maximum Parsimony and Bayesian analyses were conducted on individual and combined datasets. All phylogenetic tree topologies showed polytomies but suggest that Mannia has evolved from within its sister genus Asterella and that the genus falls into two main clades. Mannia is paraphyletic with Asterella gracilis a close relative to M. triandra and M pilosa. Because of incongruent tree topologies morphological and molecular data sets were not combined. Based on mainly spore characters in combination with molecular results a new infrageneric classification of Mannia is presented.