The primary examples of non-seed vascular plants are ferns and horsetails. They possess vascular tissue that is efficient at carrying water and enables them to grow larger than non-vascular plants. They reproduce and spread using spores rather than seeds.
Spores are reproductive single cells that ferns and horsetails release into the wind. They are extremely lightweight, so they can be carried long distances before they settle and begin growth. The spores do not grow into the familiar forms of ferns, but instead into tiny gametophytes that produce eggs and sperm. The sperm they produce must swim through a layer of water to find and fertilize another gametophyte, so ferns and horsetails usually rely on damp environments to reproduce. Some species have evolved to survive in drier environments. Once fertilized, the egg in a gametophyte begins to grow into the sporophyte.
The sporophytes of ferns and horsetails are the larger and much more obvious versions of these plants. This is a reversal from earlier in plant evolution, where the gametophyte is the larger, dominant stage. It is the sporophyte that produces spores. While the sporophyte has two copies of each chromosome, the spores it produces and the gametophytes that grow from them have only one copy.