Vegetative anatomy and its systematic significance in the Dryadella Luer (Orchidaceae: Pleurothallidinae)

Dryadella comprises 54 neotropical species with a disjunct distribution in the Andean region and the Atlantic Rainforest. This work investigated the vegetative anatomy of 13 species of Dryadella, and Masdevallia infracta selected as an outgroup, to search for distinctive characteristics of the genus, characters to differentiate disjunct Atlantic Rainforest and the Andean groups, and the traditional infrageneric classification, based mainly in vegetative characters. Twenty-seven anatomical vegetative characters were analysed in light microscopy-LM and scanning electron microscope-SEM and evaluated by Cluster and Principal Coordinates Analysis - PCoA. Results from statistical and Cluster analysis exhibited morpho-anatomical similarity among Dryadella species. PCoA indicated separation between Dryadella ataleiensis and D. pusiola from other species with average support by silhouette analysis. The two most relevant characteristics to distinct clusters were the shape of the ramicaul in cross-section, and the ornamentation of leaf cuticle in the adaxial surface. Statistical analyses indicated that endemic groups of the Atlantic Rainforest and the Andean region do not present morpho-anatomical differences, and infrageneric sections are not supported by the characters investigated. This similarity may be related to the recent origin and rapid diversification of species, as shown in previous studies on Pleurothallidinae. Therefore, the morpho-anatomical characters observed here are stable and may be useful for taxonomy and genus characterisation.