For many years, scientists thought that the earliest land plants resembled liverworts, which are small and flowerless green plants with leaf-like stems or lobed leaves. Liverworts tend to occur in very moist habitats.
Senior author Philip Donoghue told Seeker that, because of this assumption about liverworts, "huge amounts of time and money have been invested in studying their genomes and developmental biology and physiology, as though they are effectively living museums. This is based largely on the basis that living liverworts lack many of the key features present in all other living land plants, like stomata."
The team's new research instead shows that today's liverworts lack these key features because they lost them over evolutionary time. While liverworts were part of one of the earliest land plant lineages, the ancestral terrestrial plant would have been more like moss, they believe.
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It remains unclear what precise factors led to plants first colonizing land, but Morris said that plant evolution must always "strike a balance between opportunities of open real estate for photosynthesis and enhanced carbon sequestration, while also dealing with the greater challenges of UV radiation, dehydration, gas exchange, and reproduction out of water."
It is intriguing to consider that, as plants were first becoming terrestrial, land-based arthropods emerged, according to recent research conducted by the University of Bristol’s Davide. The large phylum Arthropoda includes insects, spiders, and crustaceans.
As animal life expanded and diversified after the Cambrian explosion, so too did plants. By the time the first dinosaurs walked the earth about 247 million years ago, plants with roots, stems, and seeds had evolved.