Structure of the seed coat of the Asteraceae species. I. Tribes Arctotideae, Cardueae, Mutisieae, Vernonieae

Abstract

The sculpture of the seeds surface and the anatomic structure of the seed coat of 35 species from 28 genera from 4 tribes of the Asteraceae: Arctotideae (Arctotis, Berkheya, Gazania), Cardueae (Acroptilon, Alfredia, Ancathia, Berardia, Carthamus, Cirsium, Echinops, Klasea, Lamyropappus, Olgaea, Onopordum, Rhaponticum, Serratula, Silybum, Synurus, Syreitschikovia, Takeikadzuchia), Mutisieae (Adenocaulon, Dicoma, Gochnatia, Jungia, Leibnitzia, Trichocline, Trixis) and Vernonieae (Vernonia) are investigated by methods of the light and scanning microscopy. The seed coat of the studied species is well developed and remains until the complete maturity of cypselas. The structure of the cells of an exotesta has a basic meaning for the characteristic of a seed coat. Cells of the exotesta have mainly one type of structure on all surfaces of the seed, however there are types at which cells of the exotesta are presented by several types. For example, Acroptilon repens has thin-walled cells alternating with thick-walled cells on all surface of the seed. The exotesta cells of Dicoma schimperi have different structure in apical and basal parts of the seed. As a result of this research it is established that the morphological differences of exotesta cells are caused by form, size, dimensional orientation of cells in relation to the seed axis and also degree of thickenings of tangential and radial walls of cells. The complex of the revealed features of a seed coat characterizes specifics of taxon at the species level. The features of seed coat structure, the characteristic for each separate tribe, are not established.

Keywords

• anatomy; cypselas; scanning electronic microscopy (sem); seed coat; systematics