The angiosperms, commonly referred to as the flowering plants, are the dominant plants in most terrestrial ecosystems, but how they came to be so successful is considered one of the most profound mysteries in evolutionary biology. Hundreds of millions of years ago, ferns and conifers were the dominant plant species on Earth; then, about 150 million years ago, angiosperms suddenly appeared, rapidly spread, and diversified to such an extent that they now comprise 90 percent of all living plant species. Charles Darwin called their proliferation an "abominable mystery," fearful that this apparent sudden leap might challenge his theory of evolution. While the cause of their high diversity has been attributed largely to coevolution with pollinators and herbivores, their ability to outcompete the previously dominant ferns and conifers has been the subject of many hypotheses. Common among these is that the angiosperms alone developed leaves with smaller, more numerous stomata and more highly branching venation networks that enable higher rates of transpiration, photosynthesis, and growth. How angiosperms pack their leaves with smaller, more abundant stomata and more veins is unknown, but Kevin Simonin and Adam Roddy have shown that this ability is linked to simple biophysical constraints on cell size. Simonin and Roddy's research provides strong evidence that the success and rapid spread of flowering plants around the world was the result of genome downsizing. Since the genome is located in the nucleus of the cell, a smaller genome allows a plant to build smaller cells. This in turn allows greater carbon dioxide uptake and carbon gain from photosynthesis, the process by which plants use light energy to turn carbon dioxide and water into glucose and oxygen, and maximizes the productivity of the plant's photosynthetic process. The researchers say that genome downsizing happened only in the angiosperms and was "a necessary prerequisite for rapid growth rates among land plants."

The author of the passage cites Darwin's sentiment toward the rapid emergence and proliferation of the angiosperms most likely in order to

(A) emphasize the importance of the enigma of the plants' success.
(B) explain the basis for Darwin's fear that his theory would be undermined.
©illustrate an example that contradicts Darwin's theory.
(D) show that the evolution of flowering plants is inconsistent with Darwin's theory.
(E) suggest that Darwin's fear that his theory would be challenged was unwarranted.



The primary purpose of the passage is to

(A)argue that Darwin's theory of evolution cannot explain the rapid emergence and proliferation of flowering plants.
(B) compare the prevalence of angiosperms to that of ferns and conifers.
(C) discuss the reasons a wide variety of species evolved within the angiosperm group.
(D) explain how flowering plants evolved smaller genomes.
(E)present evidence suggesting an explanation for the remarkable efficiency and productivity of flowering plants.