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Plant Systematics and Evolution

, Volume 151, Issue 3–4, pp 187–202 | Cite as

Floral mimesis inThelymitra nuda (Orchidaceae)

  • Peter Bernhardt
  • Pamela Burns-Balogh
Article

Abstract

Insect pollination occurred inThelymitra nuda R. Br. on sunny days when the ambient temperature exceeded 20 °C. The flower buds on a raceme opened subsynchronously displaying the brightly-colored, actinomorphic perianth and exposed the contrastingly-colored, scented and ornamented column. InT. nuda the staminodes and the filament of the fertile stamen are fused to one another producing an inflated hood over the anther. This staminodal hood is terminated in two non-ornamental, but brightly-colored, central lobes and two terete lateral lobes bearing approximately 400 white trichomes. Each trichome bears a double chain of 30–40 spherical, rugulose cells. Female bees, in the genusLasioglossum (Halictidae), were observed to land directly on the hood and curled their bodies around the four lobed tip of the staminodal complex. The bees attempted to forage on the lobes as if they were collecting pollen from fertile, poricidal stamens. These bees applied thoracic vibration to the yellowish central lobes and actively scraped the trichome clusters (Pseudopollen) with their forelegs. Bees carried the pollinaria ofT. nuda dorsally on their abdomens. Abdominal contact with the rostellum appeared to occur when the female bee disengaged herself from the staminodal hood. Observations made of bees on co-blooming flowers, and analyses of pollen loads collected by bees suggested that the orchid flower mimics the guild of blue-purple flowers that lack floral nectar but offer pollen in poricidal anthers. The models ofT. nuda are co-bloomingLiliaceae in the generaDichopogon andThysanotus. However, nectarless, buzz-pollinated flowers are also extensively distributed over the orchid’s range. More than 30% of the flowers in theT. nuda population had their pollinaria removed, suggesting a high capacity for cross-pollination in an orchid genus usually considered to be self-pollinated via mechanical autogamy. This study confirmed previous predictions that column modifications represented a trend towards pseudanthery.

Key Words

Angiosperms Orchidaceae Thelymitra nuda Liliaceae Dichopogon Thysanotus Halictidae Lasioglossum Syrphidae. — Mimesis pollinaria staminodal hood thoracic vibration trichome cluster. — Flora of Australia 

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Copyright information

© Springer-Verlag 1986

Authors and Affiliations

  • Peter Bernhardt
    • 1
  • Pamela Burns-Balogh
    • 2
  1. 1.Department of BiologySt. Louis UniversitySt. LouisUSA
  2. 2.Department of BotanySmithsonian InstitutionWashington, DCUSA

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