The spectrum of sexual forms in the forest flora of the Central Ciscaucasia

We examined the sexual status of each of 683 species in the forest flora of the Central Ciscaucasia. In 36.9% (252 species) of seed plants in this flora we found eight forms of sexual differentiation: gynodioecy (79 species, 11.6%), monoecy (55 species, 8.1%), andromonoecy (45 species, 6.6%), gynomonoecy (33 species, 4.8%), dioecy (29 species, 4.2%), polygamomonoecy (5 species, 0.7%), androdioecy (5 species, 0.7%) and trioecy (1 species, 0.1%). Widespread occurrence of gynodioecy (11.6%) most likely reflects an overall high proportion of this sexual form in angiosperms in the temperate zone of the Earth. In the forest flora of the Central Ciscaucasia a high proportion of diclinous species is found in dicotyledonous plants and a low proportion of non-hermaphroditic species -in monocotyledonous plants (39.8 and 25.7%, respectively). Subclasses of angiosperms differ both in degrees of sexual differentiation and in diversity of the spectrum of sexual forms. In our study, at the family level, 40 of 89 families in the forest flora only contain hermaphroditic taxa (Alliaceae, Caprifoliaceae, Fumariaceae, Juncaceae, Orchidaceae, Orobanchaceae, Potamogetonaceae, Primulaceae, Rubiaceae, Solanaceae, Violaceae, etc.). 24 of 89 families have mixed sex expression types (hermaphroditic and non-hermaphroditic) within a family (Poaceae, Asteraceae, Rosaceae, Apiaceae, Fabaceae, Brassicaceae, Scrophulariaceae, Lamiaceae, Cyperaceae, Caryophyllaceae, etc.). Of 89 families of angiosperms, 25 families include species with only unisexual flowers: Aceraceae, Betulaceae, Chenopodiaceae, Euphorbiaceae, Salicaceae, Sparganiaceae, Typhaceae, etc. At the genus level, 195 of 334 genera only contain hermaphroditic taxa (Allium, Epilobium, Festuca, Juncus, Lathyrus, Orobanche, Potamogeton, Rosa, Rubus, Scrophularia, Trifolium, Veronica, Vicia, Viola, etc.); 39 of them include hermaphroditic and non-hermaphroditic taxa (campanula, cerastium, Geranium, Potentilla, Polygonatum, Ranunculus, Silene, Verbascum, etc.), 100 of them are exclusively non-hermaphroditic taxa (Acer, Betula, carex, chenopodium, Euphorbia, Populus, Rumex, Salix, Stellaria, Typha, etc.). Sexual forms of plants have different sets of tools for xenogamy, as well as different flowering strategies and tactics: dioecy (complete idiogamy exclusion), gynomonoecy (presence of sporophytic self-incompatibility systems), andromonoecy (increasing the number of staminate flowers and strict protandry of flowers and whole inflorescences), gynodioecy (xenogamy in female plants) and monoecy (clearly expressed protogyny). Different types of forests (beech, oak, ash, poplar, willow and alder) are characterized by similar values of proportion of non-hermaphroditic species, which ranges from 36.9 to 41.3%.

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