AOBPreview originally published online on March 5, 2004
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Annals of Botany 93: 499-505, 2004
© 2004 Annals of Botany Company
Lip Anatomy and its Implications for the Pollination Mechanisms of Bulbophyllum Species (Orchidaceae)
1 Departamento de Ciências Farmacêuticas, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, Ribeirão Preto, SP, 14040-903, Brazil, 2 Departamento de Ciências Biológicas, Universidade Estadual de Feira de Santana, Rod. BR 116, km 03, Feira de Santana, BA, 44031-460, Brazil and 3 Departamento de Botânica, Instituto de Biologia, Universidade Estadual de Campinas, CP 6109, Campinas, SP, 13083-970, Brazil
* For correspondence. E-mail spadua{at}fcfrp.usp.br
Received: 10 September 2003; Returned for revision: 7 December; Accepted: 6 January 2004 Published electronically: 5 March 2004
• Background and aims The lip structure of six Brazilian and one Asiatic species of Bulbophyllum with wind-assisted fly pollination (B. involutum, B. ipanemense and B. weddellii) and non-wind-assisted fly pollination (B. epiphytum, B. glutinosum, B. regnellii and B. rothschildianum) was studied to investigate the presence of secretory tissues related to these pollination mechanisms.
• Methods The lip study was carried out through scanning electron microscopy (lip surface) and light microscopy (anatomical features).
• Key Results In most of the species studied, the osmophores (odour glands) were located in the lobes and in the upper surface of the lip callus. Differences in the lip structure were observed between the two groups (the presence of a nectary and the extent of osmophore surface), depending on the mechanism of pollination. Nectaries were found in the cavity callus in B. ipanemense, B. involutum and B. weddellii, even though their pollinators were presumably attracted by the instinct to oviposit.
• Conclusions These findings corroborate the hypothesis that, because pollination in these species is dependent on an unpredictable external factor (wind), nectar is necessary to keep the insect in the flower for a long period. Despite the occurrence of a liquid-like nectar in the flowers of B. epiphytum, B. glutinosum, B. regnelli and B. rothschildianum, no anatomical evidence for nectaries was found in the lips of these species, although a similar structure may occur in another region of the flowers. This observation agrees with the fact that pollination by lip movement in the latter species requires only gravity, with no additional mechanism being needed to keep the flies in the flower.
Key words: Anatomy, Bulbophyllum, nectary, Orchidaceae, osmophores, pollination, scanning electron microscopy.
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