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Look to the lilies

作者:印氟各    发布时间:2019-03-07 11:18:01    

By Bob Holmes FORGET the botany you learnt in school—even if it was only last year. It looks as if a brand-new family tree, unveiled in St Louis, will overturn many old ideas about who’s related to whom in the world of green plants. “Ever since Darwin, people have been speculating on this stuff, but it was more akin to art criticism than to science,” says Brent Mishler, a botanist at the University of California at Berkeley and one of the leaders of a five-year, 200-person effort to build a more rigorous plant family tree. In the past, botanists had to rely on their intuition and plants’ physical appearance to classify species. But now molecular biologists have worked out the DNA sequences of dozens of genes in a rapidly growing list of plants, creating a rich new source of evolutionary information. And in the past few years, botanists have developed objective ways of combining all the available information to determine the phylogeny, or family tree, that best fits all the observations. Mishler and his colleagues chose representative species spanning the breadth of green plant diversity, and completed their work just in time for the botanical congress. “Now we have a bigger, more comprehensive phylogeny for the green plants than we have for the animals,” he says. The new family tree looks different from the old one in several important ways. For example, the broad-leaved plants, or dicots—once thought to represent a single group of flowering plants—turn out to be several separate lineages, some of which are more primitive than both other dicots and narrow leaved grasses, or monocots. Water lilies, for instance, are one such group. The new family tree also identifies the most primitive “living fossil” among the flowering plants, a small flower called Amborella—so little known that it has no common name—that grows only on the Pacific island of New Caledonia. Until recently, many botanists also thought that land plants evolved twice, with one lineage leading to mosses and liverworts and the other to ferns and higher plants. But the new tree shows unequivocally that all land plants evolved from a single common ancestor. However, other experts on classification warn that the new family tree is unlikely to be the last word on green plants. “We’re at the stage where it looks very simple,” says John Taylor, who studies fungi at the University of California at Berkeley. “As we learn more, we’re not going to be so smug.” More on these topics:

 

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