The surprising genealogy of the orchid. Evolved at least 90 million years ago - long before today's flowering plants
orchid. Photo: Ariel Shalit
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There are elegant orchids, some flashy, some sensational and some just weird. But even though these unusual flowers have thrilled plant lovers for centuries, evolutionary biologists struggle to place them in the plant family tree and identify their relatives.
Now, scientists say, studying the DNA of orchids is turning up plenty of surprises. The main one is that orchids actually belong to the asparagus series - they are closer to these vegetables than to the more showy flowering plants that they were previously associated with. "They are so strange, so different from anything else," said Dr. Ken Cameron, an orchid researcher at the New York Botanical Garden in the Bronx.
Another discovery is that orchids, long considered a late product of plant evolution, are actually very ancient and appeared more than 90 million years ago.
For the most part, experts easily identify the creatures closest to a certain organism, but sometimes - as in the case of orchids - the appearance can be misleading, leading in many directions or in no direction at all. One of the problems is that the orchid flowers have undergone considerable evolutionary developments. Orchids have evolved a variety of forms and subparts, sometimes to attract certain pollinating animals. In the process, elements of the flower's structure that might have indicated its evolutionary history may have been distorted or lost.
One of the oddities of orchid flowers is related to their unusual reproductive structure. The reproductive organs, which are usually separated, have fused during evolution into a single organ within a typical orchid flower. "You look into an orchid and say, 'Where are all the pieces?'" says Cameron. "This flower is like nothing else."
The DNA tests expanded the range of findings of the researchers, who until now were content with direct observations. They compared a large variety of gardens, between the orchids themselves and between orchids and other flowering plants. Cameron and his colleagues discovered that orchids undoubtedly belong to the Asparagus series. "People found it hard to believe," Cameron said. But the asparagus series is large and diverse, and includes the amaryllis, the onion, the iris and the daffodil, as well as the agave and yucca flowers.
Scientists say the evolutionary history of orchids has been blurred by the unusual characteristics of their pollen. While the pollen of most plants is almost indestructible, the pollen of orchids is often extremely fine and leaves no trace in the form of fossils. "In other plant groups, you can find a fossil and conclude from it that the group should be at least the same age as the fossil," said Dr. Mark Witten, a botanist at the Florida Museum of Natural History, "but regarding orchids, this is mostly speculation."
Now, when genetic information is used to build an evolutionary tree of these plants, it turns out that the orchids formed their own branch at a fairly early stage - they were the first of the asparagus series. The orchid branch is also older than the palm branch, and since there are palm fossils that are 90 million years old, orchids cannot be younger.
The evolutionary tree also showed that the orchids grew on the ground and in the course of evolution moved to cling to other plants. This finding indicates that it is possible that growing on trees, which are a less utilized habitat, helped orchids develop the large variety of species that characterizes them.
But according to Cameron, even though the DNA tests provided these answers, researchers could have found clues to the orchid's history even earlier if they had not focused exclusively on the conspicuous and magnificent orchid species.
One of the intriguing aspects of the plants belonging to the asparagus series is that their seeds are enclosed in a unique, black and hard shell. Since most orchids have very thin seed pods, the chances of them being relatives seemed slim. But Cameron discovered that the seed type of some of the more unknown orchids matched that of asparagus. He pointed out that the Neovidia, an unusual orchid from Borneo, and the Vanilla orchid, which produces the vanilla used in food preparation, have seeds of this type.
In fact, Cameron points out that the tiny black dots characteristic of some types of vanilla ice cream are actually those black, hard-shelled seeds, showing the orchids' obvious connection to asparagus. And hence the answer to a long-standing scientific riddle has been on the tip of the tongue for a long time.
New York Times
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