Xeromorphic leaf types: evolutionary strategies and tentative semophyletic sequences [Acantholippia, Anarthrophyllum, Chuquiraga, Junellia, Mulinum Perezia, ecophysiological anatomy, involution, deflexion, revolution, convergences, semophylesis, evolutionary canalization, South America]
1979
Boecher, T.W. (Copenhagen Univ., (Denmark). Inst. for Planteanatomi og Cytologi)
In order to achieve a versatile and more profound understanding of xeromorphic structure, a detailed anatomical study of leaves from a number of South American xerophytes was undertaken. Ecophysiological and leaf ontogenetic viewpoints were incorporated as well as attempts from a semophyletical angle to look into the background or history of the characters under discussion. Ecophysiological considerations concerned adaptations for withstanding night frosts, drought and overheating. Other topics studied were water absorption from and loss to the atmosphere, and water flux and storing in the apoplast, as well as stomatal distributions and the occurrence and function of air-filled lacunae and various types of trichome. Morphological features included marginal involution, deflexion and revolution, dorsiventrality, the cataphyll-foliage leaf relation, prophyllspines, microphylly and the cushion life form. The discussion concerns problems of multiple adaptation, the meaning of xeromorphism, types of convergent evolution, semophylesis in relation to evolutionary canalization, and finally the delimitation of xeromorphic leaf types. Species treated in detail belong to the genera: Acantholippia, Anarthrophyllum, Chuquiraga, Junellia, Mulinum and Perezia.
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