"Primitive" Vascular Plants

For convenience, we will group several lineages together because they have several things in common:

1. The sporophyte is the dominant stage in the life cycle.
2. The gametophyte is reduced, but still free-living.
3. These plants all contain vascular tissue (true xylem and phloem), differentiated, generally well developed organs (stems, roots, and leaves), and specialized reproductive structures.

The primitive vascular plants appear very early in the fossil record. While the earliest of these groups consisted only of stems and sporangia or groups of sporangia as specialized organs, later groups demonstrate true leaves and roots and, in some cases, strobili (reproductive structures, sometimes called cones). These groups dominated terrestrial plant life for much of the early history of life on land. Many of them diversified and some even became tree-sized and formed extensive forests in the wet, tropical climates of the time. The great Carboniferous forests covered much of the land during the time just prior to the age of the dinosaurs. Most of the larger members of these plant lineages became extinct during climatic changes that followed, and for most groups very few representatives remain. The extant members of these groups (except for some tree ferns) are usually relatively small. Examine the dominant sporophytes of the following groups: