White Egret Orchid: Rare Flower Species With Frilly Petals To Stabilize Pollination

In the seepage slopes and grassy wetlands throughout South Korea, Japan, China, and Russia, a terrestrial orchid thrives with pure white petals resembling a snowy egret in flight. Formally named Habenaria radiata, the white egret orchid is known for forming small basal rosettes that look like small tricyrtis.

Since ancient times, the pure white petals of Habenaria radiata have been loved by many people. However, its characteristic jagged shape's adaptive significance remains a mystery.

Discovering the Secret of White Egret Orchid

To solve this mystery, a multi-institutional research group studied the orchid's fringed petals as well as the behavior of its pollinators. The collaboration consisted of Associate Professor Suetsugu Kenji and student Abe Yusuke of Kobe University Graduate School of Science, Asai Takeshi and Matsumoto Shuji of Himeji Tegarayama Botanical Garden, and Hasegawa Masahiro of Osaka Museum of Natural History.

The research team conducted A fringe removal experiment in a natural setting to discover the role of petal shape in the reproductive success of the white egret orchid. It is widely accepted that the main function of the petals is to serve as a visual attractant to insects. The researchers hypothesized that the role of the fringe is to get the attention of hawkmoths, the white egret orchid's primary pollinator.

The hawkmoth relies heavily on its vision to recognize flowers, so big flowers with a fringe get its attention easily. It was assumed that fringed flowers have adapted to attract hawkmoths easily because they can conserve more resources when compared to fringeless flowers of the same size.

It can be predicted that removing the fringe of the orchid will reduce the fruit production rate since it indicates the number of times a pollinator visits the flower. However, the study reveals that fruit production did not decline in plants with removed fringe, indicating that the fringe does not have an important role in attracting the hawkmoths. Furthermore, it was found that eliminating fringe in the flowers results in a lower rate of healthy seeds in the fruits, unlike those with intake fringe.

The researchers also performed a detailed behavioral observation of hawkmoths to explore the relationship between pollinator behavior and a reduced number of healthy seeds. It was revealed that hawkmoths do not hover continuously while sipping nectar from white egret orchid. Instead, they grasp onto the fringe of the petal using their midleg. Therefore, it was believed that the fringe provided stability for hawkmoths, allowing them to pass on as much pollen as possible to the orchid.

Evolution of Petal Shape for Orchid Pollination

Most angiosperms or flowering plants depend on animals like bees to help them deliver the pollen grains from the stamen to the stigma. As the insects transport the pollen grains, they receive a reward in the form of nectar. This mutualistic relationship between flowers and insects affects the diversity of flower shapes.

The flower shape has dramatically evolved in some orchid species, such as the moth orchid (Phalaenopsis Aphrodite). Most orchids have at least three petals in their flower, one large and stand out from the other. Biologists believe that this formation of petals evolved along with the insects that serve as their main pollinators.

Most orchid species prefer particular kinds of insects as their pollinators. Because of this, it was assumed that the differences in the petals' structure resulted from orchid evolution aimed at attracting specific insect species.