Pollen Morphology of Eriobotrya and Rhaphiolepis (Rosaceae): Implications for Generic Delimitation and Systematics

The generic delimitation of the two closely related Rosaceae genera, Eriobotrya and Rhaphiolepis, has not yet been investigated by a detailed study of their pollen morphology using scanning electron microscopy. To provide novel diagnostic features and insights into their relationships, we examined the pollen grains of thirty-one species of Eriobotrya and Rhaphiolepis, analyzing five quantitative and two qualitative morphological variables. The findings revealed that Eriobotrya and Rhaphiolepis pollen grains are tricolpate monads that are small to medium in size and vary in shape from prolate to perprolate, predominantly featuring striate ornamentation. Notably, striate-perforate and psilate exine sculptures were found only in Eriobotrya species, while scabrate ornamentation was unique to Rhaphiolepis. The rugulate pattern appeared in both genera. Eriobotrya (E. malipoensis K.C.Kuan) had the smallest pollen grains and the shortest distance between the apices of two ectocolpi, while Rhaphiolepis (R. integerrima Hook. & Arn.) had the largest. Multivariate cluster analysis separated all species from both genera into two distinct clusters. Cluster I contained all Eriobotrya species, whereas Cluster II included all Rhaphiolepis species, demonstrating their morphological distinctness and alignment with recent micro-morphological and molecular evidence. Furthermore, the pollen profile of E. seguinii Cardot ex Guillaumin affirms its taxonomic placement within Eriobotrya. We conclude that pollen morphology offers diagnostic information for delimiting these genera. The observed ornamentation pattern of a shared striate background, with distinct derived ornamentation in each genus, provides a clear morphological foundation for evolutionary investigations within the Maleae tribe. To further clarify generic boundaries and evolutionary processes, future research should integrate these palynological data with micromorphological analyses of other plant parts and genomic information.