Perfected loneliness
Orchids have come up with a few ideas to always recruit an insect or even a bird, a bat or a frog as a willing pollinator. But what does an orchid do that blooms in an insect-poor area where there isn't even a wind that could carry the pollen to the next bloom?
It is a pitiful little plant: The orchid Holcoglossum amesianum grows on tree trunks in Chinese mountain forests at an altitude of 1200 to 2000 meters and flowers from February to April of all times, when it is the dry season there. Insects are rarely seen at this time of year and are therefore unlikely to be pollinators. There isn't even a wind blowing, which could take over this service in an emergency - certainly not favorable conditions for ensuring the transport of the pollen to its destination.
But H. amesianum wouldn't be a real orchid if it hadn't found a clever way to guarantee pollination even under such adverse conditions. This species of orchid goes its own way, as LaiQiang Huang's team from Tsinghua University in Shenzhen has now observed on almost 2000 flowers of this species.
As a first measure, H. amesianum simply gives a damn about contact with its conspecifics and is content with itself: it decides on self-pollination, which is rather rare in orchids. As a second measure, she developed a sophisticated technique for positioning the pollen precisely on its own pen - although this is spatially separated from the pollen-producing anther by the rostellum typical of orchids.
The orchid proceeds as follows: When the flower is fully open, the cap that previously covered the pollen packet (pollinium) sitting on a stalk folds away. Now the stalk begins to stretch, first tilting forwards and then downwards, maneuvering the pollinium around the rostellum, which protrudes like a nose out of the flower. Once it has circumvented this obstacle, the stalk bends further and further backwards and upwards until finally the pollen packet arrives precisely on the style. The pollinium thus describes a circle of almost 360 degrees on its journey to the female part of the flower and has to brace itself against gravity at times.
Not all flowers succeed in this feat, but about half of all pollen packets reach their destination safely - and once this has been achieved, fertilization is almost guaranteed.
H. amesianum fertilizes itself exclusively with this sophisticated technique, which has not been observed in any other flowering plant so far, cross-pollination is completely foreign to it. The scientists suspect that this self-pollination mechanism is an adaptation to the dry and insect-poor habitat and believe it is possible that other species in similar areas also use this pollination technique.
