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AOBPreview originally published online on September 26, 2008
Annals of Botany 2008 102(6):899-909; doi:10.1093/aob/mcn180
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© The Author 2008. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Comparative Anatomy and Morphology of Nectar-producing Melastomataceae

Isabela Galarda Varassin1,*, Darin S. Penneys2 and Fabian A. Michelangeli3

1 Universidade Federal do Paraná, Departamento de Botânica, Centro Politécnico, Curitiba, PR 81531-980 Brazil
2 Department of Botany, California Academy of Sciences, Golden Gate Park, San Francisco, CA 94118, USA
3 New York Botanical Garden, 200th Street and Kazimiroff Blvd, Bronx, NY 10458, USA

* For correspondence. E-mail isagalarda{at}ufpr.br

Received: 12 May 2008    Returned for revision: 8 July 2008    Accepted: 15 August 2008    Published electronically: 26 September 2008

Background and Aims: Most neotropical Melastomataceae have bee-pollinated flowers with poricidal anthers. However, nectar rewards are known to be produced in about 80 species in eight genera from four different tribes. These nectar-producing species are pollinated by both vertebrates and invertebrates.

Methods: The floral morphology and anatomy of 14 species was studied in six genera of nectar-producing Melastomataceae (Blakea, Brachyotum, Charianthus, Huilaea, Meriania and Miconia). Anatomical methods included scanning electron microscopy, and serial sections of paraffin-embedded flowers.

Key Results: All vertebrate-pollinated melastome flowers have petals that do not open completely at anthesis, thus forming a pseudo-tubular corolla, while closely related species that are bee pollinated have rotate or reflexed corollas. In most species, nectar secretion is related to stomatal or epidermal nectaries and not filament slits as previously reported. Moreover, the nectar is probably supplied by large vascular bundles near the release area. Blakea and Huilaea have nectary stomata located upon the dorsal anther connective appendages. Brachyotum also has nectary stomata on the anther connectives, but these are distributed lengthwise along most of the connective. Meriania may release nectar through the anther connective, but has additional nectary stomata on the inner walls of the hypanthium. Miconia has nectary stomata on the ovary apex. Charianthus nectaries were not found, but there is circumstantial evidence that nectar release occurs through the epidermis at the apex of the ovary and the lower portions of the inner wall of the hypanthium.

Conclusions: Nectar release in Melastomataceae is apparently related to nectary stomata and not filament slits. The presence of nectary stomata on stamens and on ovary apices in different lineages suggests that the acquisition of nectaries is a derived condition. Nectary location also supports a derived condition, because location is strongly consistent within each genus, but differs between genera.

Key words: Blakea, Brachyotum, Charianthus, Huilaea, Meriania, Melastomataceae, Miconia, nectaries, nectary stomata, pollination


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