Monograph of the Genus Radula Subgenus Amentuloradula (Radulaceae, Marchantiophyta)
Chatchaba Promma, Matt A. M. Renner and Rui-Liang Zhu
Illustration of Radula caledonica
242 pp.
8 January 2025
ISBN: 978-1-943751-17-4
Abstract. Radula (Marchantiophyta: Radulaceae) is one of the largest genera of liverworts with wide dis-tribution and high species diversity in wet tropical and subtropical regions. Five subgenera, Amentuloradula, Metaradula, Odontoradula, Radula, and Volutoradula, are currently accepted in this genus. Circumscription of taxa within Amentuloradula, however, has been challenged by homoplasy and morphological plasticity. In this study, a worldwide revision of subg. Amentuloradula, we present a comprehensive phylogenetic analysis and recognize 34 species in two sections: Amentulosae (30 species) and Longilobae (four species). The five accepted subgenera of Radula are all supported in the phylogeny, and subg. Amentuloradula is distinguished from the other subgenera by a combination of character states. Most of the species in this subgenus can be recognized by the presence of microphyllous and/or amentulose branches (absent in some species and sect. Longilobae), absence of the perigynium (present in some species and sect. Longilobae), having ovoid to ellipsoidal capsules containing a few hundred large (30–50 μm) spores or long-cylindrical capsules containing thousands of small spores in sect. Longilobae. Species are defined by the possession of two or more diagnostic morphological characters and monophyly. Molecular phylogenetic evidence, which is congruent with morphological results, supports the resurrection of the following five taxa: R. caledonica is reinstated from synonym of R. formosa, R. spicata is reinstated from synonymy of R. formosa as R. formosa var. spicata, R. recurvilobula is resurrected from the synonym of R. amentulosa, R. sainsburyana and R. vagans are resurrected from the synonym of R. helix. Radula ligula and R. flavifolia are newly resolved as members of subg. Amentuloradula. Radula iwatsukii and R. scariosa var. nodulosa are proposed as new synonyms of R. scariosa. Seven new species are described: R. cathayanafrom China, R. ectophylla from Malaysia, R. resupinatiramosa from Malaysia and Papua New Guinea, R. subamentulosa from Fiji, R. tambuyukonensis from Malaysia, R. trapezoides from China, Indonesia, Malaysia, and Thailand, and R. yangioides from Malaysia and Thailand. Species of subg. Amentuloradula are distributed from Tropical and Subtropical Asia to Australia, New Zealand, and the Pacific to South America. The centre of diversity is in Australasia with 15 species occurring in the region. A key to sections and species of subg. Amentuloradula is provided, and each species is fully described and illustrated with a complete synonymy, detailed data on habitat and distribution, line drawings, color plates, and SEM plates. With the revision, the number of Radula species is raised to 245.