Seed Plants

The first known seed plants occurred in the fossil record about 360 million years ago during the Devonian period. These photosynthetic vascular plants produce seeds, and all are heterosporous. Seed plants are unique because a mature megagametophyte and an immature young plant are contained together in a drought resistant case, the seed coat, which may allow for longer survival periods if germination conditions are not suitable.

Seed plants have stems, true roots, and leaves with a cuticle and stomata for aerial gas exchange. Most have non-flagellated or non-motile sperm and require other pollination vectors such as wind, insects, or birds.

Unlike many nonseed plants, the sporophyte is the larger, dominant generation which maintains itself by photosynthesis and nutrient uptake. The gametophyte, however, is greatly reduced and nutritionally dependent on the sporophyte.

Seed plants are separated into two divisions: