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Sztein et al. characterize IAA (auxin) metabolism in liverworts, mosses, and tracheophytes in order to explore its roles in land plant evolution. Their data appear to define two strategiesa biosynthesis-degradation strategy for regulating free IAA levels in liverworts vs. a conjugation-hydrolysis strategy in mosses and tracheophytes. These different metabolic strategies may have influenced the developmental mechanisms operating in land plant evolution. (see p. 1544)
Evolution of vegetative propagules
Moody, Diggle, and Steingraeber explore the evolutionary origin of the vegetative propagules of Mimulus gemmiparus (Scrophulariaceae), an annual in which sexual reproduction is very rare. Comparative developmental analysis of M. gemmiparus and the presumed sister species Mimulus guttatus shows that the evolution of the propagule, a bulbil, has involved both the incorporation of features present in shoots of M. guttatus and the acquisition of novel features. (see p. 1512)
Endosperm development in Platanus
Floyd et al. describe endosperm development in Platanus (Platanaceae), a basal eudicot. Comparison with several closely and distantly related taxa points to greater diversification of endosperm construction patterns than previously thought. Their study provides a model for future work on the evolution of reproductive characters in the angiosperms, and brings us one step closer to an understanding of the remarkable events associated with the origin and early radiation of flowering plants. (see p. 1523)
Serpentine ecology
Rajakaruna and Bohm give the first description of soil/plant variation within a serpentine site, using two physiologically differentiated races of Lasthenia californica (Asteraceae) growing in the Jasper Ridge Biological Reserve of Stanford University. Their study emphasizes the importance of physiological adaptations to different edaphic conditions as a driving force in the diversification of flowering plants. (see p. 1576)
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