Foliar Trichomes of Pleurothallidinae (Orchidaceae): Functional Significance

Foliar surfaces of nine pleurothallid orchids (Cryptophoranthus lepidotus L. O. Wms., Octomeria sp., Pleurothallis pidax Luer, P. poeppigii Lindl., P. revoluta (Ruiz & Pav.) Garay, Restrepiella ophiocephala (Lindl.) Garay & Dunsterv., Restrepia muscifera Rchb. f. ex Lindl., Scaphosepalum rapax Luer, Stelis endresii Rchb. f.), four nonpleurothallid orchids (Cyrtopodium punctatum (L.) Lindl., Encyclia cochleata (L.) Lemee, E. tampensis (Lindl.) Small, Paphiope‐dilum hybrid) and five tillandsioid bromeliads (Catopsis nutans (Sw.) Griseb., Tillandsia fas‐ciculata Sw., T. streptophylla Scheidw., T. stricta Soland., T. tectorum E. Morr.) were assayed for permeability to Ca, S and P ions. Compared to leaves of the atmospheric bromeliads, those of the orchids proved less permeable to Ca and S. Moisture exchange profiles were determined for two of the bromeliads and three orchids; bromeliad leaves were able to rehydrate completely, orchid leaves only partially. Absorptive capacities of trichomes borne by five taxa were tested by autoradiographic analysis. Unlike bromeliad trichomes, those of the orchids exhibited no capacity to accumulate 3H‐leucine. These results and other considerations described here suggest that, unlike tillandsioid bromeliads, neither the pleurothallid nor the nonpleurothallid orchids examined in this survey rely heavily on shoots for mineral and moisture procurement.