Weird enough that suggestions like this make it into the scientific literature:
Given the large number of new genes with different GC structures in grasses, perhaps the lineage was initiated by a wide hybridization event with another species that had genes with a high GC content, followed by selective gene retention and loss to create today’s Poaceae. The wide hybridization, while most likely to have involved a plant species, could have been prokaryotic or algal and, a prokaryotic origin could explain the higher proportion of intronless Poaceae-specific genes (1).
The above text comes from a paper published just two years ago (one year before the publication of the maize genome) describing the sequence of thousands of maize genes. It’s a wild claim — hybridizing with a prokaryote (bacteria) or algae not the wide cross part — and one I personally don’t think is very likely. But the reason people can make it with a straight face is because grasses are so different from everything that came before them, and so successful.
Grasses look and act almost nothing like the species they’re related to — the grass family belongs to the same order (the next organizational step up) as pineapples. They’re flowering plants but have either discarded things as basic to flowers as petals or modified them into something completely unrecognizable (the petals and sepals of other flowering plants might have become the lemmas, paleas, and/or lodicules of grasses). Grasses have also reversed course from most flowering plants that depend on birds or insects to carry pollen from one plant to another and gone back to good old wind pollination. Yet, without the necessity of appealing to different pollinators to drive speciation, the grass family still encompasses more than ten-thousand species. And in the 50 or so million years or so since the major grass families split from each other, they have reshaped a whole quarter of the earth’s surface (2) creating whole new ecosystems (grasslands) that never existed before.
- Nickolai N Alexandrov et al., “Insights into corn genes derived from large-scale cDNA sequencing,” Plant Molecular Biology 69, no. 1 (January 2009): 179-194.
- H. L. Shantz, “The Place of Grasslands in the Earth’s Cover,” Ecology 35, no. 2 (April 1954): 143-145.