Mosses + hornworts

Non-vascular plants Bryophyta Ulva and Chlamydomona Mosses, liverworts, hornworts 24,000... 

Bryophyta Bryophytes, liverworts, hornworts, mosses 31,600 No specialized vascular tissues and no real roots must absorb moisture from their aboveground environment. 

The liverworts are one of three classes in the plant phylum Bryophyta. The other two classes are mosses and hornworts. Liverworts are small, green, terrestrial plants. They do not have true roots, stems, or leaves. Instead, they have an above ground leaf-like structure, known as a thallus, and an underground structure, known as a rhizoid. Most liverworts are found in moist environments and they tend to be less resistant to desiccation than their relatives, the mosses. Many liverwort species are found in temperate North America, but most species grow in the tropics. 

Like mosses and hornworts, liverworts are restricted to moist environments for two principal reasons. First, they lack a vascular system for efficient transport of water and food. Second, their sperm cells must swim through water to reach the egg cells. 

There are only a few fossils of liverworts and mosses and there are no fossils of hornworts. This is because the soft tissue of these bryophytes does not fossilize well. The oldest known liverwort fossil is from the late Devonian period, about 350 million years ago. Most botanists believe that they originated long before this. 

Among the land plants, two large groups with more than 30 000 species depend on water for fertilization [32, 35, 73, 85, 98], These are the Bryophyta or liverworts, hornworts, and mosses, and the Pteridophyta or lycopods, horsetails, and ferns. In both groups, two generations alternate between the gametophyte and the sporophyte plant. Within the... 

A resource devoted to mosses, liverworts, and hornworts from Southern Illinois University, Car-bondale... 

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