Plants in the Ordovician Period escape the oceans

The Ordovician period, 490 million years to 443 million years ago, has the continents of Laurentia, Balitic, Siberia and Gondwana separating further. The world is warm and moist at the beginning of this era.

Algae moves from salty seas and invades some fresh water areas on the planet.

Liverwort appears next. This is a low growing plant, with dark green ribbon like leaves. Liverwort begins to climb out of the ocean onto the surrounding land, but not very far and mostly into caves along the water’s edge. It has no vascular system to carry water to parts of the plant not in water so it can not travel far. It produces spores, with male and female cells. When the spore is fertilized a stalk forms carrying the fertilized spore away from the plant 3″ or so. The spore then splits open and the spores with in are released. Liverwort has survived to this day but not quite the same as it was then. Liverwort Riccia is likely the closest to the liverwort of the Ordovician era.

The first mosses appear at the edge of the land during the Ordovician era. Like liverwort they have no vascular system so must remain in wet areas so the water will be carried to all their parts. But they make their own food using sunlight.

Fungi are in the water at this time. The fungi that gets dumped on shore forms an alliance with algae dumped on shore and together they create lichen.

It is not easy for the plants to escape the water onto land. First they have to deal with gravity. There won’t be any water buoyancy to hold them upright. Second they don’t yet have a way to move moisture from the water supply to areas of the plant away from water. They also have no way to waterproof the cells to keep the moisture in but let CO2 and O2 exchange. Despite this the plants move onto the land a few million years before the critters are able to do so.

Right now liverwort and mosses are the only plants to lack vascular systems to transport water.

This era began warm but ends as one of the coldest the planet will see. Most of the land is covered in ice and is shifting deeper over the south pole. The oceans are shallow, most of the water is in ice sheets covering a good part of the land. Most of our critters are going to be extinct when this period is done.

More information:
Study shows how ancient plants and soil fungi turned the Earth green
Learning to live on land, how some early plants overcame an evolutionary hurtle