AOBPreview originally published online on May 24, 2004
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Annals of Botany 94: 129-132, 2004
© 2004 Annals of Botany Company
Pseudopollen in Dendrobium unicum Seidenf. (Orchidaceae): Reward or Deception?
1 School of Earth, Ocean and Planetary Sciences, Cardiff University, PO Box 914, Park Place, Cardiff CF10 3YE, UK and 2 School of Biosciences, Cardiff University, PO Box 915, Cardiff CF10 3TL, UK
* For correspondence.
Received: 28 January 2004; Returned for revision: 1 March 2004; Accepted: 15 March 2004. Published electronically: 24 May 2004
• Background and Aims In 1987, Kjellsson and Rasmussen described the labellar trichomes of Dendrobium unicum Seidenf. and proposed that these hairs function as pseudopollen. Pseudopollen is a mealy material that superficially resembles pollen, is usually laden with food substances and is formed when labellar hairs either fragment into individual cells or become detached from the labellum. However, the trichomes of D. unicum are very different from pseudopollen-forming hairs found in other orchid genera such as Maxillaria and Polystachya. Moreover, Kjellsson and Rasmussen were unable to demonstrate the presence of food substances within these trichomes and argued that even in the absence of food substances, the hairs, in that they superficially resemble pollen, can still attract insects by deceit. The aim of this paper is to investigate whether the labellar trichomes of D. unicum contain food reserves and thus reward potential pollinators or whether they are devoid of foods and attract insects solely by mimicry.
• Methods Light microscopy, histochemistry and transmission electron microscopy.
• Key Results Dendrobium unicum produces pseudopollen. Pseudopollen here, however, differs from that previously described for other orchid genera in that the pseudopollen-forming trichomes consist of a stalk cell and a ‘head’ of component cells that separate at maturity, in contrast to Maxillaria and some Polystachya spp. where pseudopollen is formed by the fragmentation of moniliform hairs. Moreover, the pseudopollen of Maxillaria and Polystachya largely contains protein, whereas in D. unicum the main food substance is starch.
• Conclusions Flowers of D. unicum, rather than attracting insects solely by deceit may also reward potential pollinators.
Key words: Amyloplast, deception, histochemistry, mimicry, protein, pseudopollen, reward, starch, transmission electron microscopy, trichome.
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