Breeding System of <i>Thymus mongolicus</i> (Lamiaceae)

Abstract

Abstract—Thymus mongolicus (Ronniger) Ronniger (Lamiaceae) is a valuable medicinal and aromatic plant. T. mongolicus is the implicitly polycentric dwarf shrub widely distributed in different environments of Tuva. The breeding system of T. mongolicus was studied in three steppe and meadow habitats. Statistically significant differences between bisexual and pistillate flowers of T. mongolicus were established based on three morphological features of the flower: the length of the upper lip of the corolla and the length of stamen filament of the upper and lower stamens (p 0.0001–0.016). The length of the upper lip of corolla of the bisexual flower is 1.3 times longer than that of the pistillate flower; the lengths of stamen filaments of upper and lower stamens of bisexual flowers are 3.7 and 4.1 times longer (respectively) than the length of staminodes of pistillate flowers. The stamens of the pistillate flowers are underdeveloped and do not form fertile pollen. The frequency of females occurrence in coenopopulations is insignificant (2.1–3.4% of the total number of generative individuals), and females are absent in some phytocoenoses. Reproduction of T. mongolicus occurs both by seed and vegetatively. The distribution of T. mongolicus individuals by ontogenetic groups showed that both pregenerative individuals (33.0–38.1% of the total number of individuals) and generative individuals (31.2–63.7%) are well represented in cenopopulations. Analysis of the ratio of genets and ramets in the steppe petrophyte coenopopulation showed the significant predominance of the vegetative individuals in all ontogenetic groups: in general, there are 3.7 times more ramets than genets. In the meadow coenopopulation, the germination of seeds and the spread of generative individuals is prevented by the relatively high total projective cover of the herbage. It can be assumed that the low occurrence of T. mongolicus females is a-ssociated with a low seed renewal and specificity of offspring inheritance.