Avyekin Y. Morphogenesis and reproductive ability of rare caudiciform succulents in the conditions of introduction

The research focuses on the features of the formation of succulent variations in caudiciform succulents from the family Apocynaceae on the pregenerative stage of ontogenesis and is aimed at finding ways of their reproduction in greenhouse conditions. We have studied three succulent caudiciform species: Adenium obesum, Petopentia natalensis, and Fockea edulis. These species are rare and endemic plants that have a protected status and are listed in the Red List of South Africa and IUCN Red List. The study of morphogenesis has defined two strategies for the development of succulent signs in the model objects. The first is characterized by the active development of the hypocotyl already at the stage of seedlings and the formation, in the future, of the extended basal part of the stem and the thick main root. The second is the formation of an expanded basal part of the stem at the stage of the juvenile plant, without modification of other organs. We have found that the formation of the extended basal part of the stem is due to the combined medullary-cortical primary thickening. The secondary thickening in immature plants in the basal part of the stem occurs in two individual ways: in A. obesum, cambium generates continuous rings of phloem and parenchymatous xylem; in P. natalensis and F. edulis retains the bundle type of the vessel elements. The thickening of the main root in A. obesum and F. edulis occurs due to the formation of parenchymatous xylem. The formation of periderm is a characteristic of seedlings A. obesum and juvenile plants of P. natalensis, F. edulis, which most likely is an evolutionary adaptation to arid climate conditions. Our research has shown that the modifications of the stems in the studied taxa according to their morphological features do not correspond to the term "tuber", "caudex" or "rootstock".