ABSTRACT
The Platanthera Rich. (Orchidoideae) comprise a speciose genus of orchids primarily in the northern hemisphere, with up to 200 known species worldwide. Individual species are known to self-pollinate, but many rely on insect pollinators with characteristics such as floral color, timing of floral odor emissions, nectar rewards, and spur length associated with particular pollination syndromes. As with many orchids, some orchid-pollinator associations are likely highly co-evolved, but we also know that some Platanthera spp. are the result of hybridization events, which implies a lack of pollinator fidelity in some cases. Some Platanthera spp. occur in large numbers which, coupled with the numerous Platanthera-pollinator systems, make them accessible as study species and useful for co-evolutionary studies. Due to the likely effects of climate change and ongoing development on Platanthera spp. habitats, these orchids and their associated pollinators should be a focus of conservation attention and management. However, while there is a fairly substantial literature coverage of Platanthera-pollinator occurrence and interactions, there are still wide gaps in our understanding of the species involved in these systems. In this systematic review, we outline what is current knowledge and provide guidance on further research that will increase our understanding of orchid-insect co-evolutionary relationships. Our review covers 157 orchid species and about 233 pollinator species interacting with 30 Platanthera spp. We provide analyses on aspects of these interactions such as flower morphology, known insect partners of Platanthera species, insect-Platanthera specificity, pollination visitor timing (diurnal vs. nocturnal), floral rewards, and insect behavior affecting pollination outcomes (e.g., pollinia placement). A substantial number of Platanthera spp. and at least a few of their known pollinators are of official (IUCN) conservation concern - and many of their pollinators remain unassessed or even currently unknown - which adds to the urgency of further research on these co-evolved relationships.
ABSTRACT
Orchids often have specific pollinators, which should provide reproductive isolation, yet many produce natural hybrids. Platanthera dilatata and P. stricta differ in floral morphology but often co-occur, overlap in flowering, and are reputed parents of P. xestesii. We used motion-triggered video detection units to monitor floral visitors of P. dilatata and P. stricta on Vancouver Island, Canada. Pollinia removal in P. dilatata was observed using histochemical staining, and cross-pollinations were performed to determine compatibility. From 1,152 h, 753 videos were recorded; 655 contained insects and 91 contained arachnids. Bumblebees, butterflies, and moths removed pollinia from P. dilatata. No pollinia removal was observed from P. stricta. Five videos showed insects moving between Platanthera species. Pollinia removal rates were low. Hand-pollinations resulted in capsule development and seed production. This study adds to the known diversity of insects interacting with these orchids, and highlights regional differences in floral visitors.
