Seed morphology of species of Spergula and Spergularia (Caryophyllaceae) occurring in Ukraine and its taxonomic significance

The micro- and macromorphological characteristics of seeds of species of the genera Spergula and Spergularia in the flora of Ukraine were studied in order to identify new diagnostic characters useful for solving taxonomic issues. The ultrastructure of the seed surface was studied using a scanning electron microscope. Seeds of some species of these genera are similar in appearance (especially with a wide wing — Spergula morisonii and Spergularia marina), which can be one of the confirmations of the close taxonomic affinity of these genera. The results of our study showed that the ultrastructure patterns of the surface of seeds of Spergula and Spergularia species differ among themselves within these genera but for some species can be used as diagnostic characters for their identification. The data obtained confirm the results of our previous research on the taxonomic status of some representatives of the studied taxa (Fedoronchuk, 2023). In particular, taking into account the similarity of seed ultrastructure and other characteristics that have been proposed previously, we consider Spergula vulgaris a synonym of Spergula arvensis subsp. arvensis, S. vernalis — a synonym of S. morisonii, Spergularia media — a synonym of Spergularia marina, and Spergularia salina — a synonym of Spergularia marina. Differences in the surface ultrastructure of Spergula sativa and Spergula arvensis subsp. arvensis, which is consistent with our understanding of the taxon (Fedoronchuk, 2023) as Spergula arvensis subsp. sativa, as well as between Spergula maxima and Spergula arvensis subsp. arvensis, accordingly we propose — Spergula arvensis subsp. maxima. Compiled descriptions of the surface ultrastructure of seeds of Spergula and Spergularia species collected in the territory of Ukraine can be used as a model for assessing the possible variability of the morphological characters of these species in other regions of the world.