鈥淔LOWERING plants are the most diverse group of plants ever to sit on the Earth,鈥� says William Friedman of the University of Colorado at Boulder. But with no obvious evolutionary predecessors, where did they come from? And how did flowering plants get to be so different from 鈥減rimitive鈥� land plants, such as mosses, ferns and conifers? Tormented by the problem, Charles Darwin called it an 鈥渁bominable mystery鈥�.
Friedman now thinks he has identified the answer in a flowering plant that provides the missing evolutionary link. The species in question is the 鈥渓iving fossil鈥� Amborella trichopoda, which is found only on the Pacific island of New Caledonia and diverged from the rest of the flowering plants 130 million years ago. Using sectioning and a variety of microscopic techniques, Friedman found that the plant鈥檚 embryo sac, which produces the egg, has a different number of cells from those of other flowering plants (Nature, vol 441, p 337).
More significantly, the pattern of cell divisions producing the egg is reminiscent of that in other seed-forming plants such as conifers, rather than in flowering plants, making it a classic 鈥渕issing link鈥� species. 鈥淚t is really fascinating as a possible holdover from primitive seed plants,鈥� says palaeobotanist James Doyle of the University of California at Davis.
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