Structural characteristics of the leaves of two species of Tetramerium an endemic to Mexico

Abstract

In taxonomic studies, in addition to floral characteristics, the structural characteristics of the vegetative organs also contribute to the taxonomic determination of the species. To provide information regarding these characteristics in the genus Tetramerium, a structural, micromorphological and histochemical analysis of cross sections of the leaves was performed using histochemical techniques and optical and scanning electron microscopy of two of its species, T. glutinosum, endemic to Mexico, and the widely distributed T. tenuissimum, was conducted. The two species presented amphistomatic leaves; double palisade chlorenchyma on adaxial and abaxial surfaces, leaf unifacial; vascular bundle sheaths with kranz anatomy; intradermal and subepidermal cystoliths of various shapes and sizes; nonglandular trichomes osteolate with a thin-walled conical head, glandular trichomes, including a new type, the straight, bright-ringed tricellular trichomes, and a variety of multicellular glandular trichomes. The glandular trichomes secrete waxes or oleoresins and mucilage deposited on the surfaces abaxial and adaxial in the form of platelets, granules and threads or strands. The histochemistry of the cystoliths highlights the presence of proteins and polysaccharides as a product of the possible superposition of the cell wall and plasmalemma lamellae. All these characteristics are typical of species from semi-arid habitats and correspond to the defense function against biotic and abiotic agents assigned to trichomes and their secretions in other studies of various genera and families, as well as to the adaptation function to these habitats of the kranz structure, which was novel for the genus Tetramerium.