The Long History of Plants

All the wars of the world,
all the Caesars,
have not the staying power
of a lily in a cottage garden.
-Reginald Farrer

Plants were probably the most important biological structure to appear on the planet. They changed the soil, the atmosphere and provided a basis for the growth of multicellular organisms. We frequently see fossils of ferns but these came relatively late in the evolutionary process even though they do predate flowering plants.

What was the first plant? Scientists believe that the first plant, and the ancestor of all plants, was the liverwort. Liverworts are very simple plants that are thought to have evolved as land plants from aquatic green algae. They have  no roots or leaves.

Liverworts absorb water through hair like structures called rhizoids. The water is transported via osmosis rather than through the xylem transport system that is present in more advanced plants. Chlorophyll is present so photosynthesis does take place. The gas exchange (carbon dioxide in oxygen out) is accompanied through simple pores rather than stomata.

While fossils of the liverwort plants have not been found what have survived are fossilized spores. Similar to spores from modern day plants, these structures have a heavy duty exterior coat which fossilizes well. The oldest liverworts spores were believed to be those found in the Czech Republic and Saudi Arabia. The spores were dated at between 461 and 463 million years old.

Recently paleontologists in Argentina set this date back to 471 to 473 million years. Researchers from the Department of Paleontology at the Argentine Institute of Snow, Ice and Environmental Research in Mendoza, Argentina collected samples of sediment from Rio Capillas, in the Sierras Subandinas in the Central Andean Basin of northwest Argentina. They dissolved these sediment samples in acid and found the ancient liverwort spores. Surprisingly, they found spores belonging to 5 different genera of liverwort indicating that land plants had already begun to diversify.

Paleontologists are now theorizing in light of this diversification of genera that land plants may have originated during the Ordovician period, 488 to 472 million years ago or during the late Cambrian period, 499 to 488 million years ago. Speculation is that they originated on Gondwana the southern mega continent that eventually divided into Antarctica, South America, Africa, Madagascar, Australia-New Guinea,  New Zealand, Arabia and the Indian subcontinent.

Given the general hardiness of plants and their long journey one sometimes wonders why the individual plant is so easy to kill.