Leaf Characteristics of the Flora of the High Plateau of Itatiaia, Brasil

Abstract

The high-mountain flora at Itatiaia, Brasil, consists of graminoid plants intermingled with evergreen shrubs with xeromorphic leaves which at first glance look all rather similar. Leaf characteristics such as leaf size, degree of hairiness, maximal potential hydration level, leaf-area development, degree of sclerophylly, and degree of succulence were determined for 30 common species. Xeromorphic features, though clearly developed in the flora, are not extreme. Leaves are small, varying from nanophyllous to mesophyllous; leaf-area development values and sclerophylly values are fairly high, and succulence values rather low. Four strategy types in the leaves of the Itatiaia species can be identified, and are discussed in terms of the cost-income model of leaves presented by Orians and Solbrig (1977). Maximal potential hydration levels are rather constant during the course of the relatively dry winter season, thus suggesting that the plants are predominantly hydrostable. For two species, variability in leaf parameters of plants occurring on sites with contrasting water conditions are discussed and interpreted in terms of their ecological amplitude. IN GRISEBACH'S (1872) WELL-KNOWN ACCOUNT of the vegetation of the world, an early attempt was made to correlate leaf morphology and climate. In 1915 and 1916 Bailey and Sinnott reported on correlations between leaf-margin features of dicotyledonous species and their distribution in the broad climatic zones of the world. Since then the theme of leaf characteristics as expressions of local macroclimate has frequently recurred in botanical literature, particularly in palaeobotanical studies (e.g., Wolfe 1971, Dolph 1979, Dolphl and Dilcher 1979). Leafsize spectra for specific vegetation types, particularly for tropical forests, have been calculated and compared as a contribution toward a characterization of the structural composition of the communities (cf. De Sloover et al. 1965b, and Werger and Ellenbroek 1978 for several references); also changes in leafsize spectra in a successional series have been compared (e.g., Barkman 1979). Leaf consistency has long been regarded as an important indicator of environmental conditions. Schimper (1898) discussed hygromorphic and xeromorphic structures in leaves in terms of adaptations to physiologically wet and dry habitats respectively. Significant contributions in this respect were the work of Huber (1925), who pointed out the importance of a plant's ability to regulate the osmotic value of its plasma under changing environmental water conditions, and the results of Miiller-Stoll (1947-1948), who complemented the findings of Firbas (1931) in showing that xeromorphic characters in bog plants diminish under nitrogen fertilization. Beadle (1966) pointed out a similar role for phosphate in Australian xeromorphic plants, and Steubing and Alberdi (1973) also showed that sclerophylly (though differently defined) increases with decreased availability of phosphate. Walter (1968, 1972, 1973; Walter and Kreeb 1970) discussed various examples of xeromorphic (or peinomorphic) features in plants stressing the great differences in water-balance strategies in xeromorphously appearing