Abstract
SUMMARYThe stomata of Arachnis cv. Maggie Oei, Aranda cv. Deborah, Arundina graminifolia, Bromheadia finlaysoniana, Cattleya bowringiana×C. forbesii and Spathoglottis plicata (Orchidaceae) occur only on the lower epidermis of the leaves and are located within hyperstomatic chambers formed by cuticular ledges extending from the guard cells. Arachnis, Aranda and Cattleya have thick leaves which exhibit Crassulacean acid metabolism, and their stomata open when acidity levels are lowest, or shortly thereafter. Aranda and Arachnis require higher light intensities for sufficient deacidification to permit stomatal opening than Cattleya. Stomata of the thin‐leaved Arundina, Bromheadia and Spathoglottis open during the day. The stomatal rhythms, morphology and distribution, as well as the pathways of carbon fixation and light requirements for deacidification, reflect the natural habitat of each species or the parents of the three hybrids.
Highlights
Arundina graminifo/ia and Bromheadia finlaysoniana have the highest density, followed by Spathoglottis plicata and Cattleya; lowest densities are found in Aranda cv
The guard cells of all six orchids have cuticular ledges which extend over the stomata! pore to form hyperstomatic chambers
The present findings show that maximum stomatal opening in these orchids can occur very early in the morning (Cattleya, Fig. 3g), just before noon (Arundina, Fig. 4g), during the early afternoon (Bromheadia, Fig. 5g and Spathoglottis, Fig. 6g), in the evening (Arachnis, Fig. lg) and at night (Aranda, Fig. 2g)
Summary
Maggie Oei (thick and leathery leaves) and Aranda cv. Deborah (Arachnis hookeriana X Vanda lamellata; thick and rigid leaves) were obtained from the nursery of the Botany Department, University of Singapore, Cattleya bowringiana X C. forbesii (very thick and very rigid leaves), Arundina graminifolia (herbaceous leaves), Bromheadia finlaysoniana (leathery, but not very thick leaves) and Spathoglottis plicata (thin leaves) were obtained from the Orchid Collection of the Singapore Botanic Gardens. Healthy and uniform mature leaves from the mid-stem region of plants of flower-bearing age were selected for observation. Plants were brought into a partially shaded courtyard one week in advance to allow for acclimatization. In the case of Arachnis and Aranda, measurements were taken on leaves of plants growing in the field. All determinations were made during 2 weeks of successive 24-h periods
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