The evolutionary tendency of gametophyte decrease persisted within the vascular plant lineage that gave rise to seed plants, while the gametophytes of seedless vascular plants may be seen.

Most seed plants' gametophytes are visible to the naked eye. This shrinkage enabled a significant evolutionary breakthrough in seed plants: small gametophytes may grow from spores held within the sporangia of the sporophyte of the parent. This setup can safeguard the environmental stressors on gametophytes.

As an example, the sporophyte's wet reproductive tissues protect the gametophytes against UV rays and keep them safe from evaporation, this connection also allows for the development.

The growing gametophytes can also get nutrients from the parental sporophyte because to this connection. The free-living gametophytes of seedless vascular plants, on the other hand, must fend for themselves.

Although a few seedless plant species are heterosporous, seed plants are unusual in that the megasporangium is retained within the parent sporophyte. The megasporangium is encased and protected by an integument layer of sporophyte tissue. Megasporangia in gymnosperms are encircled by a single integument, but those in angiosperms are generally enclosed by two.

The entire structure—megasporangium, megaspore, and integument(s)—is referred to as an ovule (as shown in the image attached).

A female gametophyte grows from a megaspore and produces one or more eggs inside each ovule (from the Latin ovulum, small egg).

There are three stages that occur from ovule to seed in a gymnosperm:

• Ovule that has not been fertilized. A fleshy megasporangium is covered by a protective layer of tissue termed an integument in this longitudinal slice through the ovule of pine (a gymnosperm). The micropyle, the single hole through the integument, permits a pollen particle to enter.

• Ovule that has been fertilized. A megaspore matures into a female gametophyte that lays an egg. A male gametophyte was found in the pollen grain that had entered through the micropyle. The male gametophyte creates a pollen tube that releases sperm, fertilizing the egg.

• Gymnosperm seedling Fertilization causes the ovule to develop into a seed, which contains a sporophyte embryo, a food supply, and a protective seed coat formed from the integument. The megasporangium dries up and dies.

Gymnosperms produce “naked” seeds, which are frequently seen on cones.

A typical gymnosperm life cycle includes the dominance of the sporophyte generation, the formation of seeds from fertilized ovules, and the involvement of pollen in transporting sperm to ovules.

Gymnosperms first emerge in the fossil record of plants and dominated numerous Mesozoic terrestrial ecosystems. Gymnosperms and angiosperms are the two monophyletic groupings of living seed plants. Cycads, Ginkgo biloba, gnetophytes, and conifers are examples of extant gymnosperms.

Flowers and fruits are examples of angiosperm reproductive adaptations (pp. 642–649).

Flowers are made up of four different sorts of modified leaves: sepals, petals, stamens (which generate pollen), and carpels (which produce ovules). Ovaries mature into fruits, which frequently transport seeds to other sites by wind, water, or animals.

Flowering plants first appeared some 140 million years ago, and by the mid-Cretaceous (100 million years ago), they had begun to dominate some terrestrial ecosystems. Fossils and phylogenetic studies shed light on the evolution of flowers.

There are several groups of basal angiosperms. Other important angiosperm clades include magnoliids, monocots, and eudicots.

Human well-being is dependent on seed plants.

Humans rely on seed plants for a variety of goods, including food, timber, and numerous medications.

The destruction of habitat threatens the extinction of many plant species as well as the animal species that rely on them.