Models of Shoot Formation in Plants in Light of Molecular Genetic Data by a Case Study of Minuartia s.l. (Caryophyllaceae): I. Monopodial Models

Molecular phylogeny has gained an increased importance in plant taxonomy in recent years. However, comparison of sequences of the particular chloroplast or nuclear genes or even whole genomes at times leads to novel and rather unexpected results in the field of plant systematics. After publication of phylogenetic data, the genus Minuartia s.l. underwent taxonomic revision, since it proved to be a paraphyletic group according to the cladistic approach. The revision revealed new and reinstated the earlier eliminated genera, including Cherleria L., which contains 19 species. The genus Cherleria is of particular interest in view of the significant habitual differences across the species. Therefore, an urgent need arises for a search for novel taxonomically significant characters to clarify the relationships between intrageneric taxa. For this purpose, we studied biomorphological characteristics of six model Cherleria spp. specimens and identified the most significant ones taxonomy-wise: specifically, shoot formation model, morphology of the cushion, shoot branching pattern, presence or absence of specialized vegetative shoots for spatial colonization, growth strategy, and structure of the monocarpic shoot. Analysis of biomorphological traits of the studied species revealed four growth strategies: (a) strategy of centrifugal propagation; (b) strategy of centrifugal propagation with sparse radially oriented specialized lateral shoots of the semi-rosette type; (c) strategy of vector propagation by active branching at the early stages of development, with subsequent “attenuation” of lateral axes formation; (d) strategy of vector propagation with semi-rosette plagiotropic shoots with the subsequent packing of the internal environment of the cushion due to orthotropic rosette shoots. Comparison of the molecular phylogeny and biomorphology data that we obtained allows us to identify biomorphological apomorphies: monopodial plagiotropic-semi-rosette–orthotropic-rosette model of shoot formation with specialized semi-rosette shoots for colonization of a territory and the presence of dicyclic monocarpic shoots; it also allows us to identify plesiomorphies: monopodial rosette model of shoot formation, formation of a tightly packed cushion, and monocyclic simply arranged monocarpic shoots. On the basis of these data, we put forward an assumption that a monopodial rosette model was the initial shoot formation model for the genus Cherleria.