The floral biology of Platanthera dilatata (Pursh) Lindl. (Orchidaceae)

Boland, J. Todd (Jeffrey Todd) (1993) The floral biology of Platanthera dilatata (Pursh) Lindl. (Orchidaceae). Masters thesis, Memorial University of Newfoundland.

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Abstract

The floral ecology of Platanthera dilatata (Pursh) Lindl. in St. Phillip's, Newfoundland, was investigated during the 1990-1992 flowering seasons. For comparison, two additional populations from eastern Newfoundland and a population from southwestern Alberta were also examined. Pollinators were restricted to the nocturnal Noctuidae and diurnal Hesperiidae. While pollinators were rarely observed, pollination exclusion experiments indicated that insect vectors are required for capsule set. Percentage capsule set for the St. Phillip's site was similar in all three seasons (range = 47.7-56.0%). Two populations from eastern Newfoundland showed similar capsule set values while the population in southwestern Alberta had significantly higher capsule set (66.8%). Capsule set was determined to be pollinator-limited. Microhabitats had no effect on capsule set. P. dilatata has a number of physical characteristics which increased its opportunity for pollination. These include an extended blooming period, sequentially-produced flowers which are long-lived, long receptivity-time for flowers and continual odour production. The adaptations are particularly advantageous during periods of unfavourable weather and low pollinator activity. Additionally, it was observed that some populations can have seed production dramatically reduced due to insect damage and fungal infection.

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