Spore variability in Hepaticae: a case study on four short-lived <i>Riccia</i> L. species

In the present study, we tested the variability of spore morphology in freshly collected plants of <i>Riccia bifurca</i> Hoffm., <i>R. glauca</i> L., <i>R. sorocarpa</i> Bisch. and <i>R. warnstorfii</i> Limpr. ex Warnst. at the individual and population scale, and examined the taxonomical power of distinct characters that are used in the literature for species delimitation in the genus <i>Riccia</i>. Spore size, number of areolae across the distal spore side, and wing width were determined from permanent preparations of spores, using three individuals of each of the four tested species. Statistical analyses, including power analyses, were carried out, in addition to evaluation using light microscopy images. Our results suggest that individual spore characteristics are subject to high variability at the individual and population level. Owing to the high dispersion of the collected data, the boundaries for these characteristics are obscured across different species. Generally, although the specific morphology of the spores does differ across <i>Riccia</i> species, several characters are too strongly specified in the literature and should be used only in a statistical context and in combination with additional, often qualitative, characters.