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AOBPreview published online on March 29, 2005
Annals of Botany, doi:10.1093/aob/mci134
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© The Author 2005. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oupjournals.org
Received October 18, 2004
Revised November 30, 2004
Accepted February 18, 2005

Article

Comparative Structure and Pollen Production of the Stamens and Pollinator-deceptive Staminodes of Commelina coelestis and C. dianthifolia (Commelinaceae)

WILLIAM C. HRYCAN 1 and ARTHUR R. DAVIS 1*

1 Department of Biology, 112 Science Place, University of Saskatchewan, Saskatoon, Canada SK S7N 5E2

* To whom correspondence should be addressed.
ARTHUR R. DAVIS, E-mail: davisa{at}duke.usask.ca


  Abstract

• Background and Aims Flowers of Commelina coelestis and C. dianthifolia provide pollen alone as a floral reward, and rely on visual cues to attract pollinators. Three stamen types, all producing pollen, occur in each of these species: two cryptically coloured lateral stamens, a single cryptically coloured central stamen and three bright yellow staminodes that sharply contrast with the blue to purple corolla. The objective was to compare the stamen structure and pollen characteristics of each of the three stamen types, and to test the hypothesis that the staminodes are poor contributors of viable pollen for the siring of seed. The pollination roles of the three stamen types and the breeding systems of both species were also explored.

• Methods Light, fluorescence and scanning electron microscopy were utilized to examine stamen morphology and pollen structure and viability. Controlled hand pollinations were used to explore the breeding system of each species. Filament and style lengths were measured to investigate herkogamy and autogamy.

• Key Results Pollen from all stamen morphs is viable, but staminode pollen has significantly lower viability. Pollen polymorphism exists both (a) between the lateral and central stamens and the staminodes, and (b) within each anther. Lateral and central stamens have thicker endothecia with a greater number of secondary cell wall thickenings than the staminodes.

• Conclusions Both species are entomophilous and facultatively autogamous. Lateral stamen pollen is important for cross-pollination, central stamen pollen is utilized by both species as a pollinator reward and for delayed autogamy in C. dianthifolia, and the staminodes mimic, by means of both colour and epidermal features, large amounts of pollen to attract insects to the flowers. Pollen from all three anther morphs is capable of siring seed, although staminode pollen is inferior. The thin staminode endothecium with fewer secondary thickenings retards staminode dehiscence.

Keywords: Commelina coelestis, C. dianthifolia, floral mimicry, deception, staminode, pollen polymorphism, pollen viability, autogamy, endothecium, raphide crystals.
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