On the structure of leaf and trichomes, and its bearing on the taxonomy of Leandra and Miconia (Miconieae, Melastomataceae).

ABSTRACT

The literature reveals difficulties in taxonomic and phylogenetic delimitations of Miconia Ruiz & Pav. and Leandra Raddi (Melastomataceae), it’s suggested that leaf anatomical characters, particularly the trichomes, can be useful within the genera. Characters related to the trichomes and leaf blade structure of 15 species of Miconieae (five species of Leandra and ten species of Miconia) were evaluated as a taxonomic criterion to separate the selected species. In addition, some considerations were made about the structure of the leaves, which can be affected by environmental factors. Leaf samples were obtained from herbaria and anatomically investigated using optical microscopy and scanning electron microscopy. Leaves are hypostomatous, dorsiventral or isobilateral, and exhibit epidermis in general with non- glandular and glandular trichomes. A hypodermis has been found only in Miconia theaezans. Conical trichomes and mixed trichomes (non-glandular and glandular) are present only in the five species of Leandra. Dendritic trichomes have been found in species of both genera. Leaf features of potential taxonomic significance are the trichome types, presence of hypodermis, number of layer palisade parenchyma, occurrence of gelatinous fibers, midrib structure, and margin structure. Xeromorphic and sclerophyllous features are present in Leandra and Miconia species, and Leandra microphylla may be considered a xerophyte.

Keywords:
Conical trichome; dendritic trichome; hypodermis; leaf margin; mesophyll structure; midrib structure.