Seasonal patterns of growth and morphology of cultivated Helleborus (Ranunculaceae)

Abstract:

The study is devoted to the investigation of ontogenesis, seasonal rhythm of development, and morphogenesis of shoots in species and cultivars of Helleborus. The phases of shoot development, as well as the order and patterns of their branching, have been established. The type of buds, their number, and the sequence of formation are described. It was found that the pre-generative period in H. purpurascens and H. ‘Red Lady’ lasted 3 years, and the full ontogenetic cycle spans several decades. The transition from monopodial growth of the axial shoot to sympodial branching in H. purpurascens begins during the generative period, whereas in H. ‘Red Lady’ it occurs during the pre-generative period. The pre-generative ontogenetic period in H. foetidus lasts 2 years, with a total development cycle of about 5 years; basiosympodial branching of shoots begins at early stages of the pre-generative period. In representatives of the Acaules group, such as H. purpurascens and H. ‘Red Lady’, lateral monocarpic shoots pass sequentially through the following phases over two years: vegetative bud, vegetative shoot, generative bud, and generative shoot. Vegetative shoots are orthotropic, shortened, with few metamers; renewal buds are formed in the axils of cataphylls, and foliage leaves lack axillary structures. In the representative of the Caulescentes group, H. foetidus, monocarpic shoots sequentially pass through the phases of vegetative bud, vegetative shoot, and mixed vegetative-generative shoot over two years; renewal buds are open, lacking protective scales. All studied species and cultivars exhibited regular mass flowering and fruiting.

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