Structure of the seed coat of the species of Asteraceae. II (tribe Heliantheae)

Abstract

We present the study of the structure of the seed coat of 52 species from 31 genera (Acmella, Ambrosia, Aspilia, Balsamorhiza, Blainvillea, Borrichia, Chrysogonum, Clibadium, Delilia, Echinacea, Eclipta, Engelmannia, Helianthella, Helianthus, Heliomeris, Heliopsis, Iva, Lindheimera, Parthenium, Ratibida, Rudbeckia, Sanvitalia, Silphium, Sphagneticola, Synedrella, Synedrellopsis, Tithonia, Verbesina, Xanthium, Zaluzania, Zinnia) of ten subtribes of the tribe Heliantheae of the Asteraceae family. The study of the seed coat structure was carried out by scanning electron microscopy. It has been established that the species of the tribe have a distinctly sculptured or smooth, well-developed testa, which remains until the full maturity of the achenes. The sculpture of the seed surface in most species is determined by the exotesta cells. The several types and subtypes of the structure of exotesta cells due to the degree and type thickening of cell walls were revealed. The sculpture of the surface of the seeds of the species that make up the tribe is diverse. The shape and specifications of the thickening of the walls of the exotesta cells within the genus and subtribe are diverse, as a result, it is not possible to identify the characters inherent in the entire Heliantheae tribe, as well as its subtribes and genera. The division of the Heliantheae tribe into subtribes is not supported by the results of our study. The conservative nature of the characters of the testa cells structure allows to use them in solving problems of taxonomy of genera, phylogenetics, to establish the degree of homogeneity of taxa united in genera and subtribes of the Heliantheae tribe.