Diverse large lepidopteran pollinators promote the naturalisation of Crinum asiaticum in invaded and disturbed habitats, despite apparent floral specialisation

Abstract

Crinum asiaticum is phenotypically specialised with white, scented, very long-tubed flowers, suggesting that only long-proboscid hawkmoths may be effective pollinators. However, this species has frequently escaped cultivation in many tropical and subtropical regions. We therefore investigated the reproductive biology of C. asiaticum to understand how it is able to naturalise, despite phenotypic specialisation. We examined the ability for autonomous selfing and reliance on sexual versus vegetative reproduction in C. asiaticum var. sinicum, using a group individuals growing and propagating naturally in a suburban botanical garden. We also analysed the floral syndrome, recorded floral visitors, determined the pollination effectiveness of floral visitors, and reviewed records of floral visitors at different observation sites. Sexual reproduction provides a much greater potential for dispersal than vegetative reproduction in C. asiaticum var. sinicum. This plant does not perform autonomous selfing and shows poor self-compatibility. The floral syndrome strongly points to long-proboscid hawkmoth pollination, whereas both hawkmoths and swallowtail butterflies with varied tongue lengths were observed as floral visitors because the nectar can accumulate to high levels and therefore fills the majority or all of the perianth tube. Both butterflies and hawkmoths effectively deposited pollen on stigmas. Thus, natural propagation should be attributed to sufficient cross pollination by local lepidopterans. Our findings suggest that autonomous selfing and vegetative reproduction may not be necessary for naturalisation and long-term persistence of plant populations in highly disturbed habitats or new ranges, even if the plants exhibit an extremely specialised floral syndrome.