Abstract
<p>Three-month-old seedlings of 11 species of the subfamily Cactoideae (<em>Melocactus bahiensis</em>, <em>Melocactus curvispinus</em>, <em>Echinopsis eyriesii</em>, <em>E. mirablis</em>, <em>E. peruviana</em>, <em>Oreocereus celsianus</em>, <em>Rebutia flavistyla</em>, <em>Rebutia minuscula</em>, <em>Astrophytum myriostigma</em>, <em>Mamillaria columbiana</em>, and <em>M. prolifera</em>) have been studied. These plants exhibit a uniseriate epidermis, covered by a thin cuticle. Except for <em>E. peruviana</em> and <em>A. myriostigma</em>, no hypodermis could be detected. The shoots of all studied specimens consist mainly of cortex parenchyma with large thin-walled cells. The pith parenchyma is composed of much smaller cells. Due to the fact that the cortex parenchyma comprises the largest portion of the cross-sectional area, it can be concluded that it is the main water-storing tissue. The extent of vascular tissue development varies. Collateral vascular bundles are present in the stele. The studied seedlings contain various ergastic substances, in particular inclusions of calcium oxalate (all studied species), starch (<em>Mammillaria prolifera</em>, <em>E. mirabilis</em>, and the genus <em>Melocactus</em>), inulin-like inclusions, and occasionally lipid drops (some <em>Echinopsis</em> species).</p><p>Thus, it was found that all studied plants have a highly specialized anatomical and morphological structure. At the same time, the epidermis and hypodermis are poorly developed. Accordingly, the adaptation to arid conditions of the examined seedlings involves an increased growth of the water-storing tissue and the production of ergastic substances.</p>
Highlights
Cactaceae is a specialized family, whose members are perennial stem succulents
The aim of our work is to study the anatomical and morphological structures of the stems of Cactoideae seedlings and to define their adaptation features at the early stages of development
Small prismatic crystals of calcium oxalate can be found in the epidermal cells
Summary
Cactaceae is a specialized family, whose members are perennial stem succulents. According to the acknowledged classification, this family includes four subfamilies, 130 genera and 1870 species [1]. Due to their ecological and biological characteristics, Cactaceae plants are sensitive to environmental changes [2]. Representatives of the largest subfamily, Cactoideae Eaton, are the most specialized succulents among four Cactaceae subfamilies. Their characteristic morphological features are the complete reduction of leaves, the presence of areoles, and the green succulent stem. Cactoideae seedlings possess a thickened succulent hypocotyl with a conical or spherical shape and diversely formed cotyledons: subulate, triangular, in the form of small tubercles, or even completely reduced [5,6]
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