Сhlorenchyma in stem of succulent plants from the genus Euphorbia L. (Euphorbiaceae)

Abstract

The necessity of photosynthesis execution by stems causes the structural and functional changes in plants. The stems of majority of succulent plants of the genus Euphorbia L. are covered only with the epidermis for a long time. In plants of some species the palisade parenchyma can appear which can be considered as a secondary or consequential tool to perform photosynthesis function by their stems. The anatomical structure of green annual stems of 23 Euphorbia species was examined. For 12 of them the palisade parenchyma has been established. The palisade parenchyma in the stem differs from such in the leaf by cells form and size as well as cells arrangement. The presence or absence of palisade parenchyma in the primary cortex indicates the level of specialization of stem tissues to perform the assimilation function. As the degree of development of palisade parenchyma depends on the amount of solar radiation, the presence and number of palisade parenchyma does not directly confirm the adaptation to the growth in conditions of a certain degree of aridity. Its appearance is could be caused also by growth under high insolation. Undoubtedly, appearance of palisade parenchyma in the stems of stem-succulent plants is correlated with reduction of leaves and probably is consequence of this.