Resumo

ELY, Francisca; TORRES, Fresia; RADA, Fermín  e  LEON, Yelitza. MORPHO-ANATOMICAL STUDY OF TWO TROPICAL CLOUD FOREST ORCHIDS. INCI [online]. 2007, vol.32, n.6, pp.410-418. ISSN 0378-1844.

The morpho-anatomical vegetative structure and water-storing strategies of two orchids of the Venezuelan Cloud Forests, Pleurothallis cardiantha and Maxillaria miniata, are described for the first time. Field work was conducted in a relatively preserved Cloud Forest and a secondary forest of the Botanical Garden of the Universidad de los Andes, Venezuela, located in the same vicinity. Botanical specimens were stored in FAA and submitted to standard plant anatomy microtechnique procedures, including SEM. Monthly leaf-water potentials were recorded during 2004-2005 in order to determine whether these species behave as typical CAM, facultative CAM or C₃ species. Both exhibit xeromorphic characters in their vegetative organs. M. mineata presents pseudobulbs as main water storing structures, thin cartaceous leaves, epidermal and sclerenchymatic tissues associated with siliceous crystals, adaxial hypodermis double layered, single-layered abaxial hypodermis, homogenous mesophyll with well developed collateral bundles, and abundant sclerenchyma. P. cardiantha, in contrast, presents moderately succulent to coriaceous leaves, adaxial epidermal cell forming papillae, heterogenous mesophyll with poorly developed vascular bundles. The water-storing tissues in this species involve the adaxial and abaxial hypodermis, as well as the acuiferous idioblasts located in the spongy parenchyma. The leaf water-potentials registered were high and remained practically invariable during the year, which suggests a typical CAM metabolism in both cases.

Palavras-chave : CAM ; Epífitas ; Maxillaria miniata ; Morfo-anatomía Vegetal; Orchidaceae ; Pleurothallis cardiantha ; Selvas Nubladas Andinas ; Venezuela .