Architectural Analysis of Representatives of the Celastrales Order: Structure and Rhythm of Shoot Development in Connection with Adaptations of Species to Different Environmental Conditions

Abstract

Despite the considerable interest of many researchers in the Celastrales order, which is largely due to the great diversity of structural features and almost cosmopolitan distribution (except for some arid regions), no comprehensive biomorphological analysis of its representatives has been undertaken so far. The goal of this work is to analyze the structural and rhythmological features of shoots and shoot systems (vegetative and reproductive) of representatives of the Celastrales order, the volume of which is accepted according to the latest data of molecular phylogenetics (APG IV). The main working tool of such an analysis is the concept of architectural models. Among the studied representatives of the order, the following architectural models are identified (Halle et al., 1978): Rauh, Attims, Champagnat, Mangenot, Scarrone, Stone, McClure, and Tomlinson. The shoot systems belong to three types: (1) polycarpic polycyclic with monopodial or acrosympodial growth and intercalary or pseudoterminal inflorescences with an orthotropic, plagiotropic, and/or mixed orientation of shoots in space and with sylleptic and proleptic shoots at the rhythm of development; (2) monocarpic mono- and dicyclic and terminal inflorescences; and (3) monocarpic monocyclic—once blooming, with sympodial growth and terminal inflorescences and with elongated or shortened shoots. In all these cases, the nature of the blooming of flowers is basipetal. For herbaceous and semiwood representatives (Parnassia, Stackhousioideae), models of shoot formation revealed by Russian biomorphologists are also used (Serebryakova, 1981): monopodial rosette (generative shoots monocarpic monocyclic, with single flowers, and terminal) and sympodial semirosette (generative shoots are monocarpic monocyclic, but with acropetal blooming of flowers in the inflorescence). The taxon as a whole is characterized by the formation of axillary complexes very different in structure and rhythms of development, which allows successfully using these features in characterizing individual species and in establishing evolutionary trends. Thus, for representatives of the Celastrales order, the structural diversity of shoot systems has been revealed which is the basis for the formation of different biomorphs. A high degree of ecological and morphological plasticity is manifested in the individual and intraspecific polymorphism of shoots, the dependence of the ratio of different types of shoots on environmental conditions, the possibility of changing the model during ontogenesis, and the formation of models of transitional character (Celastrus, Tripterygium). The possibility of rapid transformation of the entire shoot system under extreme environmental conditions by the example of the genus Parnassia and the subfamily Stackhousioideae is shown.