Taxonomic implications of seed morphology in Melocactus (Cactaceae) from Cuba

Although Melocactus is the second-most diverse cactus genus in Cuba, there is still no consensus regarding species circumscription. Seed morphology has not been used for classifying species in this group in Cuba, despite the taxonomically useful data obtained in some other genera of Cactaceae. In this study, seeds were evaluated for all Melocactus taxa known from Cuba, and seed morphological variability was analysed. Seed descriptions for each studied taxon (or localities) are presented here. We analysed 10 quantitative, and 19 qualitative characters in 50 seeds of 14 accessions. Seeds of the native species of Melocactus of Cuba are small to medium-sized, which place them among the smaller in the Cactoideae, and their shape is circular to broadly oval. Our results show that seven quantitative and six qualitative characters evaluated were suitable to distinguish among taxa. Such characters allowed establishing a general seed pattern for the M. matanzanus and M. curvispinus group, however, seeds in the M. harlowii group were less distinguishable using these characters. Colliculate relief characterized seeds of the M. matanzanus group with the testa border not expanded, while the M. curvispinus group seeds were identified by their ventro-apical keel. The most useful characters for species delimitation in the M. curvispinus group were seed length, and hilum-micropylar region characters. Significant characters that reveal differences within the M. harlowii group are lustre, seed relief and testa border expansion.