Seeds are produced by a specific group of plants called seed plants, which fall into two categories: flowering plants (angiosperms) and non-flowering seed plants (gymnosperms). Together, these two groups account for the vast majority of plant life on land. Not all plants make seeds, though. Ferns, mosses, and liverworts reproduce using tiny spores instead.
Flowering Plants: The Largest Seed Producers
Flowering plants, or angiosperms, are by far the most abundant seed producers on Earth. They include everything from grasses and wildflowers to oak trees and apple orchards. What sets them apart is that their seeds develop inside a protective structure: the ovary of a flower, which eventually becomes a fruit.
The process starts when pollen reaches the flower’s female structures. Flowering plants use a unique system called double fertilization. Two sperm cells from a single pollen grain each fuse with a different cell inside the ovule. One creates the embryo (the baby plant), and the other creates the endosperm, a starchy tissue that feeds the embryo as it grows. Meanwhile, the outer layers of the ovule harden into a seed coat that shields the whole package. The ovary surrounding the seed swells into a fruit, whether that’s a juicy peach, a dry bean pod, or the papery husk around a grain of wheat.
Gymnosperms: Seeds Without Fruit
Gymnosperms are the older branch of the seed-plant family. The name literally means “naked seeds,” because their seeds develop on exposed surfaces rather than inside a fruit. Conifers like pines, spruces, and firs are the most familiar examples. Cycads and ginkgo trees also belong to this group.
In most gymnosperms, seeds form on the scales of cones. Female cones contain structures called ovules, each of which holds a single cell that divides to eventually produce an egg. Pollination often happens in a surprisingly elegant way: a sticky droplet oozes from a tiny opening in the ovule, catches drifting pollen grains, then retracts to pull them inside. Once a sperm cell from the pollen fuses with the egg, a zygote forms and begins developing into an embryo. The surrounding tissue of the female cone provides starch to nourish the growing seed. When the cone matures and opens, the seeds are released, sometimes with a papery wing that helps them catch the wind.
What Triggers a Plant to Make Seeds
Seed production doesn’t happen on autopilot. Plants coordinate it with environmental conditions to give their offspring the best shot at survival. Light, temperature, water availability, and even the presence of pollinators all influence when a plant flowers and, consequently, when seeds form. Plants that need long summer days to bloom, for instance, won’t flower until the photoperiod (hours of daylight) crosses a specific threshold.
Internal chemistry matters too. Plant hormones act as signals between developing seeds and the rest of the plant. Research in tomatoes has shown that a hormone called abscisic acid, produced by developing seeds inside a fruit, sends a signal back to the plant that helps regulate how many more flowers it produces. In effect, the seeds a plant has already made influence whether it keeps making more. This kind of feedback ensures the plant doesn’t overcommit its energy.
Why Seeds Were an Evolutionary Breakthrough
Before seed plants evolved, all land plants reproduced with spores. Ferns and mosses still do. The catch with spore-based reproduction is that sperm cells need to swim through a film of water to reach the egg. That limits these plants to moist environments and makes reproduction unreliable in dry conditions.
Seeds solved two major problems at once. First, pollen replaced swimming sperm, meaning fertilization no longer depended on water. Pollen grains can travel on wind or insects across enormous distances, spreading a plant’s genes far beyond its immediate surroundings. Second, the seed itself is a survival capsule: it wraps an embryo in a protective coat along with a food supply and can remain dormant until conditions are right for growth. This allows plants to disperse their offspring across both space and time. A seed can wait out a drought, a harsh winter, or even centuries of unfavorable conditions before germinating.
The most dramatic example on record is a date palm seed recovered from the ruins of Masada, a fortress near the Dead Sea. Estimated to be about 2,000 years old, it was successfully germinated in 2005 and grew into a seedling nicknamed “Methuselah.”
How Long Seeds Take to Develop
The time from pollination to a fully mature seed varies enormously depending on the species. Some fast-growing weeds can produce viable seeds in as little as 7 to 9 days after pollination. Many garden vegetables and annual flowers take a few weeks to a couple of months. At the other end of the spectrum, pine cones can take two to three years from pollination to seed release, spending a full growing season just completing fertilization before the embryo even begins to develop.
The Range of Seed Sizes
Seeds span an astonishing range. The smallest belong to orchids, which produce dust-like seeds so tiny they’re nearly invisible to the naked eye. A single orchid pod can release millions of them. At the opposite extreme, the double coconut (also called the coco de mer) produces the world’s largest seed, a massive nut that can weigh over 40 pounds. The size of a seed generally reflects its strategy: orchid seeds carry almost no food reserves and rely on symbiotic fungi to nourish them after germination, while the double coconut packs enough energy to sustain a large seedling on nutrient-poor island soil.
Plants That Don’t Produce Seeds
It’s worth knowing which plants fall outside the seed-producing club. Ferns reproduce by releasing spores from small clusters on the undersides of their leaves. Mosses and liverworts also use spores, and their reproduction still depends on water for the sperm to reach the egg. Algae, while not technically land plants, also reproduce without seeds. These groups thrived long before seed plants appeared and continue to fill ecological niches where their reproductive strategies work well, particularly in damp, shaded environments.