Gymnosperms reproduce through seeds that develop on exposed surfaces, typically inside cones, rather than enclosed in fruit. The process relies on wind (and occasionally insects) to carry pollen from male cones to female cones, where fertilization can take anywhere from a few weeks to over a year depending on the species. Unlike flowering plants, gymnosperms never produce flowers or fruit, and their seeds sit “naked” on the scales of cones or similar structures.
Male and Female Cones
Gymnosperms produce two distinct types of cones on the same tree or, in some species, on separate trees. Male cones (called staminate cones) are usually smaller and shorter-lived. They contain tiny sacs where cells divide to produce pollen grains, each of which will eventually carry sperm. Female cones (called ovulate cones) are typically larger and woodier. Inside their scales sit the ovules, each containing the tissue that will produce an egg cell after a series of cell divisions.
In pines, the familiar woody pinecone you pick up off the ground is the mature female cone. The male cones are much less conspicuous, often appearing as small, soft clusters near branch tips in spring before shedding their pollen and falling off.
Pollination by Wind and Insects
Most gymnosperms are wind-pollinated. Male cones release enormous quantities of pollen, visible as yellow dust clouds around conifer forests in spring. A tiny fraction of those grains lands between the scales of a female cone and reaches the ovule.
When an ovule is ready for pollination, it secretes a sticky droplet through a small opening called the micropyle. This pollination drop is an aqueous fluid containing sugars, amino acids, calcium, and defensive proteins. Pollen grains land on it, get pulled inward as the droplet retracts, and are delivered to the interior of the ovule where they can germinate. The droplet’s chemistry may even favor pollen from the same species by controlling sugar composition, giving the tree a basic mechanism for screening out foreign pollen.
Wind is the dominant pollination method across conifers, but some cycads and members of the gnetophyte group rely on insects to carry pollen between cones.
Pollen Tube Growth and the Long Wait
Once a pollen grain reaches the ovule, it germinates and begins growing a pollen tube, a narrow channel that will eventually deliver sperm to the egg. In gymnosperms, this process is dramatically slower than in flowering plants. A spruce pollen tube, for example, grows at roughly 20 micrometers per hour. Flowering plant pollen tubes grow at 300 to 1,500 micrometers per hour, sometimes reaching the egg within minutes or hours.
In pines, the timeline is especially drawn out. Pollination occurs in spring, the pollen tube enters the ovule tissue, and then growth stops entirely. The tube goes dormant from midsummer until the following spring. Fertilization finally happens about 13 months after pollination. The seeds then mature and drop in late summer or early fall of that same year, making the full cycle from cone bud to seed dispersal roughly three years long in species like eastern white pine.
Other gymnosperm families move faster. Most species of cypress and some other conifers complete the journey from pollination to fertilization in just a few weeks.
Swimming Sperm in Cycads and Ginkgo
Conifers and gnetophytes deliver non-motile sperm through their pollen tubes. Cycads and ginkgo trees do something far more ancient: they produce large, multiflagellated sperm that actually swim.
In these groups, the pollen tube grows into the ovule tissue but swells at its base and bursts open, releasing the sperm into a fluid-filled chamber near the egg. The sperm then swim toward the egg cell, apparently attracted to chemical signals from the surrounding tissue. Researchers observing the sperm of the sago palm (a cycad) found that sperm cells changed direction and repeatedly approached specific cells near the egg as if drawn to them. This swimming fertilization is a holdover from the earliest land plants and exists nowhere else among living seed plants.
Double Fertilization in Gnetophytes
One surprising twist in gymnosperm reproduction involves the gnetophytes, a small but unusual group that includes joint firs, gnetum trees, and welwitschia. In Gnetum gnemon, each pollen tube produces two sperm that each fuse with a separate egg cell, creating two diploid embryos per pollen tube. This is a rudimentary form of double fertilization, though it differs from the version seen in flowering plants (where the second fertilization creates a nutrient tissue called endosperm). In gnetophytes, both fertilization events simply produce embryos, only one of which typically survives to maturity.
Seed Structure
A gymnosperm seed has three components packed together: the embryo (the next-generation plant), a food reserve, and a protective seed coat. What makes gymnosperm seeds distinct is the origin of their food reserve. In flowering plants, the nutritive tissue is endosperm, formed during fertilization. In gymnosperms, the food reserve is the female gametophyte tissue itself, which is haploid, containing only one set of chromosomes. The seed coat comes from the parent tree. So a single gymnosperm seed actually contains tissue from three different stages of the life cycle: the outer coat from the parent sporophyte, the haploid food reserve from the female gametophyte, and the diploid embryo from the new generation.
Seed Dispersal
Once seeds mature, gymnosperms use several strategies to spread them. Many pines produce winged seeds that spiral away from the cone on the wind. But wind is only part of the story, especially for larger-seeded species. In a study of four Sierra Nevada pine species, lodgepole pine (with tiny 8-milligram seeds) was almost exclusively wind-dispersed. Jeffrey pine and sugar pine, with seeds 20 to 30 times heavier, also started with wind dispersal when cones opened, but animals removed over 99 percent of those seeds from the ground within 60 days. Nearly all seedlings of those larger-seeded species actually grew from caches buried by squirrels and birds rather than from seeds that simply blew to the ground.
Some gymnosperms skip wind entirely. Yews and ginkgo trees surround their seeds with fleshy, colorful coatings that attract birds and mammals, which eat the flesh and deposit the seeds elsewhere.
Fire-Triggered Seed Release
Some gymnosperms hold their seeds in reserve for years, waiting for the right environmental signal. Lodgepole pine produces serotinous cones, sealed shut by a resinous bond between the scales. These cones stay closed on the tree at maturity and can accumulate over many years. When a wildfire passes through and heats the cones to 45 to 50 degrees Celsius, the resin melts, the scales open, and stored seeds pour out onto freshly cleared, nutrient-rich ground. Normal summer soil temperatures can also open cones that have fallen to the forest floor.
This strategy makes lodgepole pine one of the most aggressive recolonizers of burned landscapes. Populations growing in areas with frequent, high-intensity fires tend to have a high proportion of serotinous cones, while populations in regions with gentler fire regimes produce more conventional cones that open on their own. The trait appears to be genetically controlled, likely by a single gene with two variants.
The Full Life Cycle
Stepping back, gymnosperm reproduction follows the same alternation of generations found in all plants, but the gametophyte generation is reduced to a nearly invisible stage. The tree you see is the sporophyte, the dominant diploid phase with two sets of chromosomes. It produces spores through cell division inside its cones. Those spores develop into tiny gametophytes: the pollen grain (male) and the tissue inside the ovule (female), both haploid with one set of chromosomes. When sperm and egg fuse, the resulting embryo is diploid again, eventually growing into a new tree.
In gymnosperms, neither gametophyte ever lives independently. The female gametophyte stays embedded in the ovule on the parent tree. The male gametophyte travels as a pollen grain but remains just a handful of cells. The sporophyte dominates the life cycle so completely that most people never realize there’s a hidden haploid generation involved at all.