Gynodioecy of Origanum vulgare ssp. gracile (Lamiaceae) in Tajikistan

Gynodioecy has been identified to occur in the herbaceous polycarpic Origanum vulgare ssp. gracile growing in Tajikistan and is here described in detail for the first time. The investigated populations of O. vulgare ssp. gracile form two types of flowers, perfect and pistillate, on different individuals. In pistillate flowers, stamens are represented by staminodes. The size of many parts of the corolla and androecium of perfect flowers is significantly larger than in pistillate flowers. Four criteria have been identified that make it possible to reliably distinguish flowers of different sexual forms: the size of the corolla and its parts, the difference between calyx tube length versus corolla tube length, the position of the anthers, and the rate of development of stamens. Perfect flowers are characterized by strictly pronounced protandry. According to the pollen/ovule ratio (from 825 to 953), O. vulgare ssp. gracile is facultatively xenogamous. Hermaphrodites predominated (from 58.9 to 76.2%) in five of the investigated populations. The frequency of females in O. vulgare ssp. gracile was shown to be most dependent on annual precipitation. Finally, we discuss the presence and distribution of gynodioecy within the genus Origanum and its adaptive significance for the existence of populations of O. vulgare ssp. gracile.