Morphological and molecular evidence reject conspecificity of Malagasy and Mascarene Parablechnum (Polypodiopsida, Blechnaceae)

Under the current treatment of the Blechnaceae, only one species of the fern genus Parablechnum is recognised in the western Indian Ocean, often referred to as P. marginatum. Two varieties are current-ly recognised within it: a type variety present in the Mascarene Islands of Reunion and Mauritius and P. marginatum var. humbertii in Madagascar. Recent molecular evidence suggested that these two varieties are not closely related, questioning their conspecific status. To collect further evidence to support a taxo-nomic decision, we performed a morphological study based on 57 herbarium specimens comparing traits from general morphology, cross section of the fertile pinnae, sporangia and spores. As a result, Malagasy specimens can be distinguished morphologically from the Mascarene ones by pinna apex and pinna sec-tion, the presence of sporangiasters and spore ornamentation. Additionally, spore size analyses resulted in statistically significant differences between both varieties. Our results, aligned with the available phyloge-netic data, support that these two taxa should be recognised as separate species and, hence, we propose the necessary new combination and provide full descriptions.

Automated summary

Through morphological study and analysis of spore size, we found that the Madagascar variety of Parablechnum marginatum can be morphologically distinguished from the Mascarene variety, and there are statistically significant differences in spore size between them. Our results, consistent with phylogenetic data, support the recognition of these two taxa as separate species.