AOBPreview originally published online on June 11, 2004
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Annals of Botany 94: 33-41, 2004
© 2004 Annals of Botany Company
Pollination and Reproductive Biology of Twelve Species of Neotropical Malpighiaceae: Stigma Morphology and its Implications for the Breeding System
1 Departamento de Biologia, Caixa Postal 549, Universidade Federal de Mato Grosso do Sul, 79070-900 Campo Grande, Mato Grosso do Sul, Brasil and 2 Departamento de Botânica, Caixa Postal 6109, Universidade Estadual de Campinas, 13083-970 Campinas, São Paulo, Brasil
* For correspondence. E-mail msigrist{at}nin.ufms.br
Received: 8 August 2003; Returned for revision: 19 September 2003; Accepted: 18 February 2004. Published electronically: 11 June 2004
• Background and Aims This study on reproductive biology examines the stigmatic morphology of 12 Brazilian Malpighiaceae species with regard to their pollination and breeding system.
• Methods The species were studied in natural populations of a semi-deciduous forest fragment. Style tips were processed for observation by SEM and pollen-tube growth was analyzed under fluorescence microscopy. The breeding system was investigated by isolating flowers within waterproof bags. Floral visitors were recorded through notes and photographs.
• Key Results Flowers are yellow, pink or white, protogynous, herkogamous and sometimes lack oil glands. While Banisteriopsis pubipetala has functional female flowers (with indehiscent anthers), 11 species present hermaphrodite flowers. Stigmas of these species may be terminal, with a slightly concave surface, or internal, consisting of a circular cavity with a large orifice, and are covered with a thin, impermeable cuticle that prevents pollen from adhering, hydrating, or germinating. Malpighiaceae have a special type of ‘wet’ stigma, where a secretion accumulates under the cuticle and is released by mechanical means—mainly rupture by pollinators. Even though six species show a certain degree of self-compatibility, four of them present a form of late-acting self-incompatibility, and the individual of B. pubipetala is agamospermous. Species of Centris, Epicharis and Monoeca bees pollinate these flowers, mainly collecting oil. Some Epicharis and Monoeca species collected pollen by vibration. Paratetrapedia and Tetrapedia bees are pollen and oil thieves.
• Conclusions The Malpiguiaceae species studied are pollinator-dependent, as spontaneous self-pollination is limited by herkogamy, protogyny and the stigmatic cuticle. Both the oil- and pollen-collecting behaviours of the pollinators favour the rupture of the stigmatic cuticle and the deposition of pollen on or inside the stigmas. As fruit-set rates in natural conditions are low, population fragmentation may have limited the sexual reproduction of these species.
Key words: Malpighiaceae, Banisteriopsis spp., Dicella bracteosa, Heteropterys intermedia, Mascagnia spp., Stigmaphyllon lalandianum, Tetrapterys spp., pollination, reproduction, stigma morphology, oil-collecting bees, Monoeca.
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