Spores of Radulaceae (Marchantiophyta) exhibit a level of micromorphological diversity far beyond expectation

Abstract

Abstract Radulaceae is one of the most isolated lineages of leafy liverworts. This family contains three genera and between 200 and 350 extant species worldwide. Most species belong to the genus Radula, which is subdivided into five subgenera and remains taxonomically challenging. In the framework of an integrative taxonomic revision of Radulaceae in tropical America, we are paying special attention to understudied features that may be taxonomically informative, such as spores. Here, we perform the first palynological evaluation of sixteen species of Radulaceae. The spores were processed by standard palynological techniques and described using light and electron microscopy. The spores of Radulaceae are isomorphic monads, apolar in species of the genus Radula and cryptopolar in Cladoradula, usually small to medium-sized, rarely large, inaperturate, with a circular to slightly elongated outline. The spore surface is ornamented with rounded elements, here called Granulate-type ornamentation, or with elongated elements, called Echinate-type ornamentation, and shows differences in each species. The palynological data, especially spore ornamentation, can make an important contribution to Radulaceae taxonomy for separating species or groups of species. The groups found here, however, do not fully correspond to generic and infrageneric circumscriptions as supported by molecular-phylogenetic evidence.

Keywords

• Cladoradula
• liverworts
• palynology
• Radula
• SEM
• taxonomy