Orchid Family Tree Explains Widespread Diversity

There are an estimated 25,000 orchid species in the world. This outnumbers mammal, reptile and bird populations combined. While botanists have long questioned the vast diversity of this flower, a recent study developed the extensive and very old family tree of orchids by sequencing gene structures of chloroplasts.

"It was surprising that many classic characteristics of orchids -- the tiny, dust-like seeds, the role of fungi in triggering germination, the fused male-female flower parts that define the orchid flower -- did not trigger the acceleration in species formation," Thomas Givnish, first author and professor of botany at the University of Wisconsin-Madison, said in a news release.

Chloroplasts transform solar energy into sugar. The researchers examined chloroplasts from 39 orchid species. Additionally, they added genetic data of 150 more species to their analysis. From this, they made connections between molecular orchid families and existing fossils, and were able to create a branching structure that indicates how many million years ago each major group of orchids originated.

According to their study, they found that extensive mountain ranges, such as the Andes and New Guinea Highlands, greatly accelerated species' diversification. Other factors included the plants' changing evolution while living on top of trees (a system known as epiphytism) while being pollinated by orchid bees, moths, or butterflies; and the development of pollinia, or packages of hundreds to thousands of pollen grains dispersed as a unit.

The researchers found three waves of accelerated speciation--the development of more biological species--beginning 60, 40 and 33 million years ago. Givnish noted that the first acceleration of speciation was sparked by pollinia, while the second, greater acceleration was sparked by epiphytism and clouds and rain in tropical mountains. The greatest acceleration of them all was the uplifting of the Andes.

"Many hypotheses advanced by previous investigators proved to be correct, but some of the defining characteristics of orchids -- their tiny seeds, their requirement for fungi to germinate, and their fused pistils and anthers -- were not themselves responsible for the high rate of orchid speciation," Givnish added in the release. "Only later, when the orchids acquired pollinia, started to grow in trees, and then colonized the cloud forests along extensive mountain ranges in the tropics, did the orchids' unrivalled diversification begin."

Their findings were recently published in the Proceedings of the Royal Society B.

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