Variable pollinator dependence of three Gastrodia species (Orchidaceae) in modified Canterbury landscapes

Pollination is an ecosystem service affected by anthropogenic activity, often resulting in reduced fruit set and increased extinction risk. Orchids worldwide have a wide range of pollination systems, but many New Zealand orchids are self-pollinating. We studied the pollination system of three saprophytic native orchids from the genus Gastrodia in modified landscapes in Canterbury, New Zealand: G. cunninghamii, G. minor, and an undescribed taxon G. “long column”. The species showed two distinct pollination systems. Gastrodia cunninghamii and G. minor were autonomous selfing species. In contrast, G. “long column” had almost no fruit set when pollinators were excluded, and was visited by the endemic New Zealand bee Lasioglossum sordidum, which acted as a pollen vector in order to produce fruit. Visitation rate by L. sordidum varied among four sites around Christchurch, and natural fruit set in G. “long column” ranged from 76% where L. sordidum were abundant to 10% where bees were not observed. Oddly, some of the highest natural fruit-set rates were at a highly modified urban site. Therefore, while some Gastrodia species are dependent on native pollinators, they can still persist in highly modified landscapes.