Sexual forms and their ecological correlates of woody gymnosperms and angiosperms in Siberia

A principal goal of comparative biology is to determine the presence of correlations between morphological and ecological characters to gain an insight into the evolution and adaptive significance of organismal traits. This approach has been used in seed plants to understand the evolution of separate sexes from hermaphroditism. 326 species of woody seed plants belonging to 80 genera and 31 families are found in Siberia. Woody seed plants are characterized by a high degree of sexual differentiation: 26 species of gymnosperms form unisexual strobili and 126 species of angiosperms have unisexual flowers. At the family level, 16 of 31 families in Siberian flora contain hermaphroditic taxa (Ericaceae, Fabaceae, Caprifoliaceae, Ranunculaceae etc.). Five of 31 families have mixed sex expression types (hermaphroditic + nonhermaphroditic) within a family (Rosaceae, Grossulariaceae, Lamiaceae, Rhamnaceae, Thymelaeaceae). For the rest of the families, 10 of them are exclusively nonhermaphroditic (Salicaceae, Betulaceae, Ephedraceae, Pinaceae, Cupressaceae etc.). At the genus level, 52 of the 80 genera only contain hermaphroditic taxa (Rhododendron, Cotoneaster, Rosa, Spiraea, Caragana, Lonicera etc.), 5 of them contain hermaphroditic and nonhermaphroditic taxa (Daphne, Ribes, Dryas, Pentaphylloides, Thymus), 23 of them are exclusively nonhermaphroditic taxa (Juniperus, Epherda, Salix, Betula, Rhamnus etc.). In woody plants of Siberia four sexual forms are revealed: dioecy (114 species; 35.0%), monoecy (29 species; 8.9%), gynodioecy (6 species; 1.8%) and andromonoecy (3 species; 0.9%). We analyzed the relationship between sexual forms of plants and a number of their ecological and biological characteristics: life forms, mode of pollination, the structural features of fructifications, habitat type, zonal group and an ecological group. It is shown that dioecious plants are likely to be microphanerophytes, hygrophytes, have Eurasian or Asian-American areas, dry fructifications and grow in harsh alpine or arctic conditions. Monoecious plants are usually trees, megaphanerophytes or mesophytes with anemophilous pollination and dry fructifications, having Eurasian areas and being the main boreal species in Siberia. We revealed a highly unequal distribution of the general number of woody plants and the ratio of diclinous and hermaphrodite species in seven floristic provinces depending on their heat supply. Future work aimed at untangling the complex web of trait correlations with dioecy in terms of their presence, cause, and priority will be critical for understanding the ecological mechanisms responsible for the evolution of separate sexes from combined sexes in flowering plants. The article contains 3 figures, 58 ref.

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