Gymnosperms: Conifers and the Pine

What are gymnosperms?

Gymnosperms are plants that make seeds, but the seeds are naked. They are not covered by an ovary or fruit. The seeds sit on the surface of the scales of a cone. Gymnosperms have no true flowers.

Main groups: conifers (pine, spruce, fir, deodar, cedar, cypress, redwood), cycads (palm-like), ginkgo (one living species) and gnetophytes like Ephedra. They have xylem and phloem, true roots, stems and leaves. Most are trees or shrubs, and most stay green all year (evergreen).

Conifers: tree shape and needle leaves

Conifers grow in cold or dry places such as mountains and northern forests. Their features fit that life.

• Cone-shaped crown: sloping branches let heavy snow slide off instead of breaking them.
• Needle leaves: narrow, with a thick waxy coat and sunken stomata. Little water is lost, which helps in frozen or dry soil.
• Evergreen: leaves are replaced a few at a time, so the tree can make food whenever it is warm enough.
• Resin canals: sticky resin seals wounds and keeps insects away.
• Strong straight trunk with soft wood made of tracheids (long cells that carry water and give strength).

Life cycle of a pine

The big pine tree is the sporophyte (2n). It makes two kinds of cones on the same tree.

1. Male cones are small and grow in clusters. Inside, cells divide by meiosis and make millions of pollen grains (n). Each grain has two air sacs that help it float.
2. Female cones are bigger and woody. On each scale are two ovules. Inside an ovule, one cell divides and forms the female gametophyte with an egg.
3. Pollination: wind carries pollen to the female cone. Most pollen is wasted, so the tree makes a huge amount.
4. A pollen grain sticks near the ovule and grows a pollen tube. This takes many months, so no water is needed for the sperm.
5. Fertilisation: a sperm reaches the egg. The zygote (2n) grows into an embryo. The ovule becomes a seed.
6. The cone ripens in about two years. The scales open and the winged seeds fly out. A seed in good soil grows into a seedling with a ring of needle-like first leaves.

Unlike mosses and ferns, gymnosperms do not need water for fertilisation, and the seed gives the baby plant a food store and a protective coat.

Importance of gymnosperms

• Timber: soft, straight wood for houses, furniture, poles and boats.
• Paper: wood pulp for paper and cardboard.
• Resin: turpentine and rosin for paints, varnish, soap and medicines.
• Food: pine nuts such as chilgoza.
• Medicine: Ephedra gives a drug that opens the airways.
• Environment: forests hold soil, slow water on slopes, store carbon and shelter animals.
• Garden and festival plants: cycads, ginkgo and Christmas trees.

Because many conifers grow slowly, we must cut them carefully and plant new ones.

Try it: cone detective

On a trip to a hill park, pick up a fallen pine cone. Dry it for a day. Do the scales open? Look between the scales for small winged seeds. Count the scales in one row. Next, drop a seed from a height and watch it spin. Compare it with a flower seed such as a pea in a pod. Which one is covered?

Key formulas and definitions

• Key term: gymnosperm = seed plant with naked seeds (no fruit)
• Key terms: cone, ovule, pollen grain, pollen tube, winged seed
• Big pine tree = sporophyte (2n); pollen and egg-bearing parts = tiny gametophytes (n)
• Order: pollen → wind → ovule → pollen tube → fertilisation → seed (about 2 years) → seedling
• Examples: pine, deodar, spruce, fir, cycas, ginkgo, Ephedra

Worked examples

Common mistakes

• Saying gymnosperms have flowers or fruits. They have cones and naked seeds.
• Thinking cones are fruits. A cone is a group of scales that carries spores or seeds.
• Believing all gymnosperms are pines. Cycads, ginkgo and Ephedra are gymnosperms too.
• Saying conifers lose all leaves in autumn. Most are evergreen.