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Ecological Aspects of Flower Evolution. I. Phyletic Evolution

L. van der Pijl
Evolution
Vol. 14, No. 4 (Dec., 1960), pp. 403-416
DOI: 10.2307/2405990
Stable URL: http://www.jstor.org/stable/2405990
Page Count: 14
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Ecological Aspects of Flower Evolution. I. Phyletic Evolution
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Abstract

1. Floral ecology received a new impetus and background by Darwin. In the beginning of the 20th century the importance of cross-pollination, selection and adaptation were doubted, but during the second quarter of this century attention increased again. 2. Biosystematic research and population genetics have given a new basis for the evolutionary importance of pollinator-specificity, floral barriers and cross-pollination, as well as for the danger of self-pollination. 3. Tropical ecology also provided support. In Cycadaceae pollination by beetles was and is important. Coniferae are a sideline. The anemophily of Amentiferae proved to be secondary, as tropical relatives are entomophilous. The tropical Polycarpicae are more primitive in respect to pollination. 4. Paleontology shows that beetles must have stood at the cradle of the flower. Clear traces of cantharophily persist in Polycarpicae and some Monocotyledones. Many "neutral and organizational" characters of the first families may have been adaptive in regard to gnawing beetles-as epigyny, syncarpy, staminodes, early sympetaly and even angiospermy itself. 5. The primitive attractions (still important in Polycarpicae) were: (a) pollen with an odor; (b) solid food tissues on sterile organs; (c) diffuse nectar secretion, leading later to nectaries; (d) deceit, trapping of non-adapted beetles by odors. Traps are still used in morphologically primitive groups and have arisen again in Orchids. This provided irregular pollination, dependent on incidental situations. 6. In regard to the differentiation of higher flowers a position is taken on the criticisms of anti-Darwinists like Goebel, Troll, Melin, Good, Nelsson, who denied the adaptive nature of specialized flower structures. Much of their criticism can be disproved, and pure morphology and physiology seem insufficient grounds. The ecological concepts of Darwin, Muller, and followers rightly took into consideration the importance of higher pollinators as regular and more reliable flower-visitors. 7. Researches on the senses of insects provide another new basis for adaptational concepts, by demonstrating the preference of bees for zygomorphy, nectarguides, dissected contours, deep flowers, and the attractive importance of other characters of flower-classes for special pollinators.

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