Gymnosperms are a group of seed-producing plants whose seeds are not enclosed within a fruit (or ovary), literally meaning "naked-seeded" plants. They represent an ancient and evolutionarily important plant group, first appearing in the fossil record approximately 360 million years ago during the Devonian period. Modern gymnosperms are classified into four main divisions: Coniferophyta (conifers — pines, spruces, firs, larches, cedars, cypresses, redwoods — the largest and most diverse group, including the tallest living trees and some of the oldest living organisms on Earth), Cycadophyta (cycads — palm-like plants with large compound leaves and massive cones, superficially resembling palms but completely unrelated), Ginkgophyta (represented today by a single surviving species, Ginkgo biloba, sometimes called the "living fossil" since it has remained morphologically unchanged for over 200 million years and once shared the planet with dinosaurs), and Gnetophyta (a diverse group including Ephedra — a shrubby plant from which the drug ephedrine is derived, Welwitschia — a bizarre Namib Desert plant that produces only two leaves throughout its entire lifespan of up to 2000 years, and Gnetum — a group of tropical vines and trees that shows the most angiosperm-like features among gymnosperms).

Like all land plants, gymnosperms display alternation of generations — alternating between a diploid sporophyte generation and a haploid gametophyte generation. In gymnosperms, the sporophyte generation is the large, dominant, familiar plant (the pine tree, cycad, or ginkgo we see), while the gametophyte generation is dramatically reduced and largely dependent on the sporophyte, never becoming free-living or photosynthetically independent as it is in more primitive plants like ferns and mosses. Male gametophytes develop within microsporangia (pollen sacs in male cones): microspore mother cells undergo meiosis to produce microspores, which develop into the male gametophyte (pollen grain), initially retained within the microsporangium until the mature pollen is shed and wind-carried to female cones. Female gametophytes develop within megasporangia within ovules on female cone scales: a megaspore mother cell undergoes meiosis, and one resulting megaspore develops into the female gametophyte (endosperm tissue with egg cells), never leaving the ovule. Fertilisation occurs when pollen reaches the ovule, the pollen tube grows to deliver sperm nuclei to the egg, forming a zygote that develops into an embryo within the seed.

The gymnosperm seed represents a critical evolutionary innovation: a self-contained developmental package allowing reproduction independent of standing water, unlike spores which require moist conditions for fertilisation in more primitive plants. The gymnosperm seed consists of an embryo (the young sporophyte), nutrient-rich endosperm tissue (the female gametophyte, which provides nutrition for germinating seedling), and a protective seed coat (derived from the integument of the ovule). In gymnosperms, this seed sits directly exposed on the surface of an open cone scale — not enclosed within any protective carpel tissue or developing into a fruit as in angiosperms. This naked condition (giving gymnosperms their name) has implications for pollination (gymnosperms typically rely on wind pollination since there is no enclosed chamber guiding pollinators) and seed dispersal (gymnosperms cannot attract animal seed dispersers with fleshy fruits, instead often relying on wings attached to seeds for wind dispersal, as seen in the characteristic winged pine seeds).

Gymnosperms and angiosperms share the innovation of seed reproduction but differ in several fundamental aspects. Seeds: gymnosperm seeds are naked (exposed on cone scales); angiosperm seeds are enclosed within fruits (ovary wall = pericarp). Ovules: gymnosperm ovules are naked on cone scales; angiosperm ovules are enclosed within a carpel/ovary. Flowers: gymnosperms produce cones (strobili); angiosperms produce flowers. Pollination: gymnosperms rely primarily on wind pollination (anemophily); angiosperms additionally use insect, bird, and bat pollination (biotic pollination) enabled by specialised flower structures. Double fertilisation: unique to angiosperms (one sperm fertilises egg → embryo; second sperm fertilises polar nuclei → triploid endosperm); does not occur in gymnosperms. Endosperm origin: in gymnosperms the endosperm is the female gametophyte (haploid); in angiosperms the endosperm is triploid (3n) arising from double fertilisation. Xylem: gymnosperms typically have only tracheids (no vessels); most angiosperms have vessel elements for more efficient water transport.