Revisión sistemática de Riella subgen. Trabutiella (Riellaceae, Sphaerocarpales)

Abstract

Species of the genus Riella have been systematically divided into two subgenera, namely Euriella and Trabutiella depending on their smooth or winged involucres. Subgenus Trabutiella is less diverse currently including only 4 species and one variety. In the context of a worldwide revision of the genus Riella, complete revision of this subgenus was conducted in order to describe species morphological boundaries and to evaluate their taxonomic significance. After this revision 7 species are recognised. Riella affinis and R. heliospora, the only monoecious species of subgenus Trabutiella. Riella heliospora can be distinguished from R. affinis by the presence of a spore wing, the lower density of spines with distinct areolae in the distal face and by the conspicuous triradate mark in the proximal face. In the dioecious group, R. cossoniana is characterised by its obovate involucres, with 8-10 large wings extending from the tip to the base, > 6 cells high and spherical spores with concave proximal face and short distal face spines < 5 μm. Riella echinata can be distinguished by its ovate involucres widest below middle, with 8- 10 short wings < 5 cells high not reaching the base of the involucre and triangular spores with conspicuous reticulate distal face with spines> 7μm. Riella gamundiae shows intermediate characters with involucres similar to those of R. echinata and spores as R. cossoniana. Riella paulsenii is characterised by its spore showing both truncate spines and papill ae. A new species is described as Riella mediterranea Segarra-Moragues, Puche, Sabovljevic, Infante & Heras, that is characterised by its acuminate involucres with 11-15 low wings < 5 cells high and its densely spinose spores with spines up to 15 μm with truncate and enlarged apices.