Systematic relevance of seed coat anatomy in the European heathers (Ericeae, Ericaceae)

The anatomy of the seed coat of the European species of tribe Ericeae (Calluna, Daboecia and Erica) of the Ericaceae family was studied, and the taxonomic importance of their characters was analyzed. The seed coat is mostly formed by a one-cell layer with thick, pitted inner walls and thin outer walls that collapse at maturity over the inner walls. The cell junctions are either raised with anticlinal walls up to four times the height of the periclinal walls or are not raised with similar values for the height of both the anticlinal and periclinal walls. Three main cell junction types were found and described. The thickness of the inner walls is variable, but there is a large overlap among the results for different species. Calluna vulgaris is the only species with no pits, and E. multiflora has a pitted pattern on its inner walls, which is distinctive from the rest of the species. Our main results agree with the external seed morphology, and valuable new data were obtained for certain groups such as the E. cinerea-E. terminalis or the E. scoparia complex. The similarities that are found in seed coat characters are not in accordance with the classical taxonomic delimitation of infrageneric groups within Erica.