Leaf secretory structures in Ceiba (Malvaceae - Bombacoideae): ontogeny, anatomy and histochemistry

Abstract

The description of secretory structures in Malvaceae is controversial, and results in conflicting interpretations. Amid conflicting interpretations, therefore, the present study aims to describe the ontogeny diversity and histochemistry in Ceiba, emphasizing the secretory structures in leaves of C. erianthos, C. jasminodora, C. pentandra, and C. speciosa. All analyzed species present mucilaginous, crystalliferous, and phenolic idioblasts. These structures are randomly arranged in the mesophyll, epidermis, petiole cortex, and parenchymatic tissue of the midrib. However, in C. jasminodora and C. pentandra, secretory structures are only found in the midrib area. The development of mucilaginous idioblasts is asynchronous and, when mature, they coalesce forming large structures full of mucilage. Clavate-type pluricellular glandular trichomes were also detected scattered randomly on both leaf surfaces. Their ontogeny is described, and histochemical tests showed the presence of lipophilic substances. Extrafloral nectaries were observed in the middle third of the midrib, on the abaxial side of the leaflets. They originate from the protoderm and ground meristem of the midrib cortex. It is expected that these results will help consolidate knowledge of secretory structures in Malvaceae, leading, in turn, to the elucidation of phylogenetic relationships.