Seed plants are classified into two main groups: angiosperms and gymnosperms. These groups represent a monophyletic lineage, indicating that seed plants evolved from a common ancestor. Unlike seedless vascular plants, seed plants exhibit a sporophyte-dominant life cycle, with their gametophytes being predominantly microscopic and developing within sporangia.

Most seed plants are heterosporous, producing two types of spores: microspores and megaspores. Microsporangia generate pollen, while megasporangia are located within ovules. Typically, both microsporangia and megasporangia are found on the same plant, although some species may have them on separate plants. The male cones, or strobili, house microsporangia, while the female cones contain megasporangia.

The ovule is a crucial structure that encompasses the megasporangium and megaspore, eventually developing into a seed post-fertilization. The integument, a protective layer made of sporophyte tissue, surrounds the ovule. Gymnosperms possess a single integument, whereas angiosperms have multiple integuments. The micropyle is the opening at the apex of the integument, allowing for the entry of pollen. In angiosperms, the ovary wall encases the ovule, which later transforms into fruit, making fruits essentially plant ovaries.

Pollen grains, which are the male gametophytes, are encased in a tough outer wall composed of sporopollenin, providing protection. These grains are produced by microspores and are essential for pollination, the process where pollen reaches the ovule. Pollination syndrome refers to the evolutionary adaptations of flower traits in response to various pollen vectors, such as wind, bees, and birds.

Seeds develop from fertilized ovules and contain the embryonic plant, which is protected by a seed coat that allows for dormancy while keeping the seed viable. Within the seed, cotyledons serve as the embryonic leaves that will sprout during germination. The endosperm, surrounding the embryo, provides nourishment for the developing plant. For instance, when consuming seeds like peanuts, the majority of what is eaten is the endosperm, while the small notch represents the embryonic plant.