The effect of floral display on fruit set in orchid populations with different pollination strategies in the Komi Republic (Russia)

Almost a third of the Orchidaceae species have a deceptive pollination strategy. In the absence of nectar, the most important factor in attracting insect pollinators may be the floral display, i.e. the number of flowers in inflorescence. However, the role of this trait in pollination efficiency is still poorly understood, both in deceptive (nectarless) and rewarding (nectariferous) Orchidaceae species. The purpose of this study was to estimate the effect of floral display and plant height on fruit set in Orchidaceae species with various pollination strategies (reward and deceptive) in the Komi Republic (northeastern European Russia). The objects of the study were six threatened Orchidaceae species. Of these, four species, Dactylorhiza cruenta, D. fuchsii, D. maculata, and D. traunsteineri, are characterised by a deceptive pollination strategy, while two species, Gymnadenia conopsea and Platanthera bifolia, offer nectar. It was revealed that deceptive Orchidaceae species bloom earlier than rewarding species, and deceptive species have a lower fruit set (35.4%) compared to rewarding species (90%). The plant height and the time of blooming were related, i.e. early-flowering species were shorter. Statistically significant correlations were found between fruit set and the number of flowers in three deceptive species, Dactylorhiza maculata, D. fuchsii, and D. traunsteineri, and between efficiency of pollination and plant height in Dactylorhiza maculata. Rewarding species, Gymnadenia conopsea and Platanthera bifolia, showed a high fruit set. The fruit set was associated neither with the plant height nor with the floral display.