Comparative anatomy of the absorption roots of terrestrial and epiphytic orchids

The present study compared roots of terrestrial and epiphytic Orchidaceae, analyzing the anatomical characteristics from an ecological point of view. The material was collected at three different sites in Minas Gerais/Brazil and was fixed in FAA. Transverse sections were obtained by freehand sections or from material previously embedded in Paraplast(R) or Historesin(R). The prominent characteristics of the epiphytic group were: significant smaller perimeter, epidermis with 3 or more cell layers, U-thickened exodermal cell walls, O-thickened endodermal cell walls, and a low ratio between the caliber and the number of protoxylem arches. The terrestrial group presented simple or multiseriate epidermis, and exodermis and endodermis with typical Casparian strips. The anatomical characteristics should have evolved with several adaptations to distinct environments during evolutionary process.