Data from: The pollination of Habenaria rhodocheila (Orchidaceae) in South China: When butterflies take sides

Habenaria is one of the largest terrestrial genera in the family
Orchidaceae. Most field studies on Habenaria species with greenish-white
and nocturnal scented flowers are pollinated by nocturnal hawkmoths and
settling moths. However, H. rhodocheila presents reddish flowers lacking a
detectable scent and fails to fit the moth pollination syndrome. We
investigated the pollinators, breeding system and functional traits of H.
rhodocheila in South China and found that two diurnal swallowtail
butterflies Papilio helenus and P. nephelus (Papilionidae) were the
effective pollinators. When butterflies foraged for nectar in the spur,
the pollinia became attached between the palpi. A triangular projected
median rostellar lobe was found at the entrance (sinus) of the spur of H.
rhodocheila. This lobe divided the spur opening into two entrances forcing
butterflies to enter their proboscides through the left or right side.
When the projection of median rostellar lobe was removed, the site of
pollinium attachment changed to the eyes of the butterflies, leading to a
higher rate of pollinium removal but lower rate of pollinium deposition.
Our quartz glass cylinder choice experiment suggested that visual rather
than olfactory cues provided the major stimuli for butterflies to locate
these flowers. Hand pollination experiments suggested this species was
self-compatible but pollinator dependent. However, the proportion of seeds
with large embryos produced in self-pollinated fruits was significantly
lower than in cross-pollinated fruits, indicating a significant inbreeding
depression. Unlike many other orchid species, fruit set was higher than
rates of pollinium removal, indicating a high level of pollination
efficiency in a species with friable pollinia. Shifts from moth to
butterfly pollination in the genus Habenaria parallel other orchid
lineages providing insights in the potential for pollinator-mediated
floral trait selection.