Scientists think they have the answer to a puzzle that confused even Charles Darwin：How flowers evolved and spread to become the most important plants on earth?
Flowering plants，or angiosperms (被子植物)，make up about 90% of all living plant species，but how they did this has been a mystery.New research suggests it is due to genome (基因组) size.
Hundreds of millions of years ago，the earth was dominated by ferns (蕨类) and conifers (针叶树) — they were the main plants on the earth.Then，about 150 million years ago，the first flowering plants appeared on earth.They quickly spread to all parts of the world.
Why angiosperms were successful and diverse on earth has been debated for centuries.Charles Darwin himself called it a “mystery”， fearing this apparent sudden change might challenge his theory of evolution.
Kevin Simonin from San Francisco State University in California US and other researchers analyzed data held by the Royal Botanic Gardens, Kew, on the genome size of hundreds of plants，including flowering plants，gymnosperms (a group of plants including conifers) and ferns.They then compared genome size with anatomical (结构上的) features.This provides “strong evidence” that the success and rapid spread of flowering plants around the world is due to “genome downsizing”．
By reducing the size of the genome，which is contained within the nucleus (核) of the cell，plants can build smaller cells.The researchers say genomedownsizing happened only in the angiosperms, and this was “a necessary condition for rapid growth rates among land plants”．,
[理解]
Decide whether the statements are true (T) or false (F)．
1．Angiosperms are rare plants in South Africa.(F)
2．The smaller genome contributed to the success and diversity of angiosperms.(T)
[积累]
1．mystery n． 谜；神秘的事物
2．due to 由于，因为
3．dominate v. 支配，控制
4．diverse adj. 各种各样的，相异的
5．apparent adj. 明显的
6．analyze v. 分析
