Liverworts

Liverworts, along with mosses and hornworts, are classified by botanists as bryophytes – non-flowering plants that lack vascular (conductive) tissue. It is possible, even likely, that liverworts were among the first plants to make the transition to life on land. Their appearance varies according to the stage in which you see them, but the plants we think of when we think of liverworts are very small (less than an inch in diameter and about 4 inches in length) and can be relatively flat, growing very close to the ground. Liverworts have two basic stages, the dominant one being the flattish, leaf-like gametophyte. It produces male sex organs (antheridia) which produce sperm and female organs (archegonia) which produce eggs. The stalked, fringed, palm tree-like structures in the photograph are egg-producing archegonia, and the stalked, lobed structures are antheridia. Both are less than an inch tall and are produced on the same plant (unlike 80% of liverwort species that produce their sex organs on separate plants). The sperm must reach an egg in order for fertilization to take place, and it usually does this by swimming through rain water or dew. Once fertilization occurs, the second stage of the plant, or sporophyte, develops. The sporophyte produces spores, some of which will grow into gametophytes and the cycle (called alternation of generations) will repeat itself.

About these ads