Architecture of the Dwarf Shrub Thymus petraeus (Lamiaceae) in the Conditions of Southern Siberia

The structure of Thymus petraeus individuals has been studied architecturally. It has been established that in the south of Siberia the species occurs in similar habitats: in true, meadow, sandy steppes and their petrophytic variants on the slopes and low rocky peaks of hills. According to the classification proposed by I.G. Serebryakov (1964), T. petraeus is a vegetatively semimobile dwarf shrub with a system of the main root that is persistent throughout its life and with rooting runners. Three architectural units that differ in the spatial position of the compound skeletal axis (orthotropic–plagiotropic, plagiotropic, and orthotropic) have been identified in the structure of T. petraeus individuals. Each architectural unit consists of the main compound skeletal axis, compound skeletal axes of the 1st order, formation shoots, branching shoots, and enrichment shoots. It is shown that the structure of individuals can be formed by repeating only two architectural units. It is established that the structure of individuals growing in the true steppes and their petrophytic variants is built at the expense of the repetition of orthotropic–plagiotropic and plagiotropic architectural units. That in sandy steppes is built at the expense of repetition of plagiotropic and orthotropic architectural units. The features of T. petraeus development in specific ecological and coenotic conditions are shown. In this regard, we have characterized (1) morphological polyvariance, which is based on changes in the structure of shoots (shortened and elongated) and the composition of architectural units (no compound skeletal axes of the 1st order or enrichment shoots); (2) dimensional polyvariance, manifested in a change in the length and number of compound skeletal axes; and (3) dynamic polyvariance, associated with fluctuations in the duration of the monopodial growth of shoots formation (from 2 to 5 years) and the architectural unit as a whole (from 6 to 20 years). The revealed modifications of architecture do not lead to a change in the life form of the dwarf shrub, but reflect the mechanisms of its adaptation.