Newly Discovered Orchid Doesn't Bother With Photosynthesis or Opening Its Flowers

A new species of orchid has been discovered on the small Japanese island of Kuroshima. Though not readily recognized as an orchid, it nonetheless resides in the tribe Epidendroideae. Although the flowers of its cousins are often quite showy, this orchid produces small brown blooms that never open. What's more, it has evolved a completely parasitic lifestyle. 

The discovery of this species is quite exciting. The flora of Japan has long thought to be well picked over by botanists and ecologists alike. Finding something new is a special event. The discovery was made by Suetsugu Kenji, associate professor at the Kobe University Graduate School of Science. This discovery was made about a year after a previous parasitic plant discovery made on another Japanese island a mere stones throw from Kuroshima (http://bit.ly/2dYN12L).

Coined Gastrodia kuroshimensis, this interesting little parasite flies in the face of what we generally think of when we think of orchids. It is small, drab, and lives out its entire life on the shaded forest floor. Like the rest of its genus, G. kuroshimensis is mycoheterotrophic. It produces no leaves or chlorophyll, living its entire life as a parasite on mycorrhizal fungi underground. This is not necessarily bizarre behavior for orchids (and plants in general). Many different species have adopted this strategy. What was surprising about its discovery is the fact that its flowers never seem to open. 

In botany this is called "cleistogamy." It is largely believed that cleistogamy evolved as both an energy saving and survival strategy. Instead of dumping lots of energy into producing large, showy flowers to attract pollinators, that energy can instead be used for seed production and persistence. Additionally, since the flowers never open, cross pollination cannot occur. The resulting offspring share 100% of their genes with the parent plant. Although this can be seen as a disadvantage, it can also be an advantage when conditions are tough. If the parent plant is adapted to the specific conditions in which it grows, giving 100% of its genes to its offspring means that they too will be wonderfully adapted to the conditions they are born into. 

As you can probably imagine, pure cleistogamy can be quite risky if conditions rapidly change. In the face of continued human pressures and rapid climate change, cleistogamy as a strategy might not be so good. That is one reason why the discovery of this bizarre little orchid is so interesting. Whereas most species that produce cleistogamous flowers also produce "normal" flowesr that open, this species seems to have given up that ability. Thus, G. kuroshimensis offers researchers a window into how and why this reproductive strategy evolved. 

Photo Credit: Suetsugu Kenji

Further Reading:

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A New Species of Parasite Discovered in Japan

A new species of parasitic plant has been discovered on the Japanese island of Yakushima. A small population was found by Suetsugu Kenji during a survey of the lowland laurel forests that cover much of the island. Despite being an authority on parasitic plants of this region, Professor Suetsugu did not recognize these plants. As such, a specimen was collected for a closer look.

An in depth examination revealed that this was indeed a new species. It has been named Sciaphila yakushimensi in honor of the island on which it was discovered. It belongs to a family of plants called Triuridaceae. They are closely related to the family Alismataceae and many members of this family have foregone photosynthesis for a parasitic lifestyle.

S. yakushimensi is what we call a mycoheterotroph. It parasitizes mycorrhizal fungi, taking the nutrients it needs and giving nothing in return. The fungi themselves are getting their nutrient needs from the trees that grow in the forest. As such, S. yakushimensi could not exist without an intact forest to support its fungal host.

This is the troubling part. Only two populations of S. yakushimensi have been discovered. Its parasitic lifestyle makes it difficult to get an accurate estimation of its numbers. These plants live most of their lives underground, only appearing when it is time to flower. Because of this, researchers are already suggesting that this species be considered endangered.

Sadly, its native forest is under constant threat of logging. Much of this region remains unprotected. Since mycoheterotrophs like S. yakushimensi rely on an intact forest capable of supporting its host fungi, any disturbance that threatens the forest can spell disaster for these parasites. Far from being a detriment to the forests in which they live, parasitic plants like S. yakushimensi can serve as a very important reminder of how crucial it is to preserve entire ecosystems rather than single species.

Photo Credit: Yamashita Hiroaki

Further Reading:

https://www.tsumura.co.jp/english/kampo/plant/090/090_01.html