Background and aims: Aeschynanthus, a Gesneriaceae genus with more than 160 species in subtropical SE Asia, has red and tubular flowers associated with sunbird pollination syndrome. However, direct evidence of exact pollinators and their efficiency is lacking. Inhabiting in the northern edge of Aeschynanthus distribution where the putatively specific pollinator sunbird is absent, A. acuminatus has changed to reddish green flower and widely opened corolla tube in Taiwan. We thus investigated the pollination biology of A. acuminatus to increase our understandings on extremely rare observation of ornithophily in Asia north of Himalayas region.
Results: Two species of passerines, Yuhina brunneiceps (カンムリチメドリ) and Alcippe morrisonia (メジロチメドリ), were observed effectively visiting A. acuminatus. The high natural fruit set (60%) and conspecific pollen transfer rate (95%) indicate high reproductive success which appears to be the result of accurate pollen placement on the pollinators. In addition, the existence of a major peak in long-wavelength (red) spectrum of floral reflectance and the copious (58.7 µl) and diluted (6.8%) nectar with abundant hexose sugars are consistent to generalized-bird pollination syndromes.
Conclusions: The complement of generalized-passerines as pollinators in A. acuminatus with high pollination efficiency appears to play an important role in successful colonization to Taiwan as we discovered its pollination traits are closely matching the generalized-bird pollination syndromes.