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Floral Conservatism in Neotropical Malpighiaceae

William R. Anderson
Biotropica
Vol. 11, No. 3 (Sep., 1979), pp. 219-223
DOI: 10.2307/2388042
Stable URL: http://www.jstor.org/stable/2388042
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Floral Conservatism in Neotropical Malpighiaceae
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Abstract

Over 950 species of Malpighiaceae grow in a variety of neotropical habitats and have evolved great diversity in habit, fruit, pollen, and chromosome number. Their flowers, in contrast, tend to be very similar in general architecture, especially in those aspects concerned with the attraction, orientation, and reward of pollinators. The flowers are visited only by Hymenoptera, principally female anthophorid bees and trigonid bees. The anthophorids collect oil from the calyx glands, mix it with pollen, and use the mixture as food for their larvae. The trigonids collect pollen. The usual character-syndrome of the flower seems to be related to and maintained by pollination by oil-bees, and was probably ancestral in the family. Pollination by pollen-collecting bees is probably secondary in many genera and has shifted to primary importance in groups that have lost the calyx glands. Other families such as Polemoniaceae, which have evolved very diverse flowers, reward pollinators with a sugary nectar that attracts a variety of secondary pollinators. This faunal diversity provides a bridge between one character-syndrome in the flowers and another. The specialized rewards and resulting lack of diversity in pollinators in neotropical Malpighiaceae explain why the flowers have remained so conservative in spite of the evolution of great diversity in other aspects of the phenotype. Calyx glands seem to have been lost in most paleotropical lines in the absence of oil-bees, but field observations on the pollination of those plants are practically nonexistent.

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