Gymnosperms are the seed plants that never evolved flowers or fruit. Their seeds sit exposed, usually on the scales of a cone. They include the pines, spruces and junipers in many backyards, along with some far stranger relatives. Their lineage is much older than flowering plants, and features that look old-fashioned, like plain needles and wind-blown pollen, are part of why they still dominate cold, dry and fire-prone land.
The Four Living Groups of Gymnosperms
- Overall: living gymnosperms fall into four groups with 88 genera and more than 1,000 species worldwide.1Encyclopædia Britannica. Gymnosperm
- Conifers: pines, firs and junipers make up by far the largest group, with about 600 to 630 species.2Wikipedia. Gymnosperm
- Cycads: small trees that look like palms, with about 338 species.3Wikipedia. Gymnosperm
- Gnetophytes: a mixed group of about 95 to 100 shrubs and other plants, including the low-sprawling desert plant Welwitschia.4Wikipedia. Gymnosperm
- Ginkgo: a group of just one species, a tall tree with fan-shaped, two-lobed leaves.5Wikipedia. Gymnosperm
In a park or garden, conifers are the easiest to place. They usually carry needles or scales, and their cones are woody or, in junipers, berry-like. Cycads have a stout trunk topped by a crown of stiff, feathery leaves, which is why people so often take them for palms. Ginkgo gives itself away with fan leaves that turn gold in autumn. Gnetophytes are rare in gardens and look the least like the others.
Conifers, cycads and ginkgo share a way of thickening their stems with water-carrying wood and a similar pattern of seed development.6OpenStax Biology. Gymnosperms Even so, those three groups are not closely related to one another.7OpenStax Biology. Gymnosperms Gnetophytes are seen as the gymnosperms most similar to flowering plants in their water-conducting tissue.8OpenStax Biology. Gymnosperms
A few common mix-ups are worth clearing up. The sago palm is a cycad, not a true palm. And not every evergreen is a gymnosperm: holly and many evergreen shrubs are flowering plants.
Reproduction Without Flowers
With no flowers to attract insects, most gymnosperms release huge amounts of pollen into the wind. Pine-type pollen often carries tiny air sacs that add surface area with little weight.9PubMed. Aerodynamics of saccate pollen and its implications for wind pollination The sacs slow how fast a grain falls, so it drifts farther.10PubMed. Aerodynamics of saccate pollen and its implications for wind pollination11PubMed. Aerodynamics of saccate pollen and its implications for wind pollination That is the yellow dust coating cars every spring. It is conifer pollen, released in enormous quantities because wind wastes most of it. It comes from the small, soft male cones, which shed their pollen and then wither. The larger woody cones you find on the ground are the female ones, and they hold the seeds on their scales, exposed rather than enclosed in fruit.
Cycads show an in-between system. They still produce swimming sperm, an ancient trait, alongside a pollen tube.12PubMed Central. Intermediate evolutionary state of motile sperm and pollen tubes in the extant gymnosperm Cycas revoluta Their pollen tubes grow slowly and are not steered toward the egg as they are in flowering plants.13PubMed Central. Intermediate evolutionary state of motile sperm and pollen tubes in the extant gymnosperm Cycas revoluta
Trees also have to grow up before they can make cones. Young pines cannot reproduce; they gain that ability only after a change into a mature phase.14PubMed. Phase-change related epigenetic and physiological changes in Pinus radiata D. Don The switch brings chemical changes in the tree’s DNA that show up right after maturity begins.15PubMed. Phase-change related epigenetic and physiological changes in Pinus radiata D. Don A young planted pine may go years without a single cone, and in many pines the seed cone then takes about two years from pollination to ripe seed.
Wood Built to Keep Water Flowing
Conifer wood moves water through narrow cells joined end to end by small openings called pits. Many conifer pits contain a disk that acts like a valve, sealing off a cell when air gets in.16PubMed. Solid mechanics of the torus-margo in conifer intertracheid bordered pits That matters because an air bubble in the wood blocks water flow to the leaves.17PubMed. Global convergence in the vulnerability of forests to drought Species whose valves seal most tightly resist drought-induced air bubbles best.18PubMed Central. Mechanism of water-stress induced cavitation in conifers: bordered pit structure and function support the hypothesis of seal capillary-seeding
These valve pits let water pass 3 to 44 times more easily than the pits in flowering-plant vessels.19PubMed. Analysis of circular bordered pit function II. Gymnosperm tracheids with torus-margo pit membranes Without this design, water flow through a conifer stem would drop by about 41%.20PubMed. Analysis of circular bordered pit function II. Gymnosperm tracheids with torus-margo pit membranes
In a drought, a tree pulls water upward under tension, much like liquid drawn up a drinking straw. As the soil dries, the tension rises, and too much of it drags air into a cell through a pit. Each blocked cell cuts the water reaching the needles. Enough blockage leaves branches browning, and it can kill the whole tree.
In a garden conifer, water stress shows first as needles yellowing or browning from the tips or from the top down. Watering deeply during long dry spells works better than watering lightly and often, and mulch around the base keeps the roots cooler and moist.
Surviving Freezing Winters
When sap freezes, dissolved air comes out as bubbles that can block cells once the sap thaws. In repeated freezing and thawing tests, juniper showed little damage and fir none.21PubMed Central. Xylem embolism in response to freeze-thaw cycles and water stress in ring-porous, diffuse-porous, and conifer species Oak’s wide vessels were the most vulnerable.22PubMed Central. Xylem embolism in response to freeze-thaw cycles and water stress in ring-porous, diffuse-porous, and conifer species The reason is size: conifer water-carrying cells are thousands of times smaller in volume than oak vessels.23PubMed Central. Xylem embolism in response to freeze-thaw cycles and water stress in ring-porous, diffuse-porous, and conifer species
Conifer wood starts losing water flow to freezing when its cells average wider than about 30 thousandths of a millimetre.24PubMed. Tracheid diameter is the key trait determining the extent of freezing-induced embolism in conifers Conifers with wide cells are as freeze-vulnerable as broadleaf trees with similar cells.25PubMed. Tracheid diameter is the key trait determining the extent of freezing-induced embolism in conifers So conifers in cold climates build narrow cells, while those in mild places use wider ones to move more water.26PubMed. Tracheid diameter is the key trait determining the extent of freezing-induced embolism in conifers
For a cold yard, pick species native to climates as cold as yours, since they build narrower wood. The riskiest time is late winter, when frozen, dry soil meets warm spells that thaw the sap and the needles start losing water the roots cannot replace. Watering evergreens well before the ground freezes helps.
Needles, Scales and Long-Lived Leaves
Juniper needles and scales have a thick outer skin covered by a waxy layer.27Acta Biologica Cracoviensia Series Botanica. ADAPTIVE MORPHO-ANATOMICAL CHARACTERISTICS OF LEAVES AND CONES IN JUNIPERUS SERAVSCHANICA KOM.: STUDIES OF POLYPHENOLIC PARENCHYMA CELLS, SECRETORY TISSUES, SCLEREIDS AND TRACHEIDS Their breathing pores sit sunk into the leaf surface.28Acta Biologica Cracoviensia Series Botanica. ADAPTIVE MORPHO-ANATOMICAL CHARACTERISTICS OF LEAVES AND CONES IN JUNIPERUS SERAVSCHANICA KOM.: STUDIES OF POLYPHENOLIC PARENCHYMA CELLS, SECRETORY TISSUES, SCLEREIDS AND TRACHEIDS Less water escapes on hot, dry or windy days.
Conifer leaves trade between tough, long-lived tissue and fast food-making.29PubMed Central. Drought resilience of conifer species is driven by leaf lifespan but not by hydraulic traits How long a conifer keeps its leaves predicts how well it bounces back from drought better than its wood traits do.30PubMed Central. Drought resilience of conifer species is driven by leaf lifespan but not by hydraulic traits Firs hold on to nitrogen mostly by keeping their leaves for years rather than shedding them.31Biogeosciences. Interactions between leaf nitrogen status and longevity in relation to N cycling in three contrasting European forest canopies
Evergreens still drop needles, because each needle lives a set number of years and then yellows and falls. Shedding of the inner, older needles in autumn is normal. Browning at the branch tips or on new growth signals a problem instead.
Some conifers are deciduous. Larches and bald cypress drop all their needles each autumn, and ginkgo sheds its fan leaves too. A bare larch in winter is not dead.
Resin and Fire-Sealed Cones
Conifers make resin in canals that store and move it through the tree.32PubMed. Resin ducts as resistance traits in conifers: linking dendrochronology and resin-based defences Resin both glues up and poisons attacking insects and fungi.33PubMed. Resin ducts as resistance traits in conifers: linking dendrochronology and resin-based defences Conifers produce a huge variety of these aromatic compounds.34PubMed. Genes, enzymes and chemicals of terpenoid diversity in the constitutive and induced defence of conifers against insects and pathogens Under attack, they shift the mix and amount of resin to fight back.35PubMed. Oleoresin defenses in conifers: chemical diversity, terpene synthases and limitations of oleoresin defense under climate change More resin canals do not always mean a tree resists pests better.36PubMed. Resin ducts as resistance traits in conifers: linking dendrochronology and resin-based defences
On a garden pine, small drips at a pruning cut are normal healing. Many small pitch tubes along the trunk often mean bark beetles. Drought-stressed trees make less resin and get attacked more.
Some pines hold seeds in sealed cones for years.37Journal of Ecology. A 350‐million‐year legacy of fire adaptation among conifers Crown fires drove this trait, and the cones release their seed after the burn.38Journal of Ecology. A 350‐million‐year legacy of fire adaptation among conifers Monterey pine cones open at about 45 °C.39PubMed Central. Seed release by a serotinous pine in the absence of fire: implications for invasion into temperate regions Hot sunny days, not only fire, can therefore open them, letting the tree spread outside fire areas.40PubMed Central. Seed release by a serotinous pine in the absence of fire: implications for invasion into temperate regions
Partners Underground
Conifer roots partner with mycorrhizal fungi, which wrap the roots and help pull nutrients from the soil. One such fungus helped Douglas fir seedlings take up more nitrogen and phosphorus when grown beside ponderosa pine.41PubMed. Ectomycorrhizal mediation of competition between coniferous tree species Pine seedlings grew more with a helpful bacterium plus root fungi than with fungi alone.42PubMed. Interaction with ectomycorrhizal fungi and endophytic Methylobacterium affects nutrient uptake and growth of pine seedlings in vitro The benefit depends on which species pair up.43PubMed. Interaction with ectomycorrhizal fungi and endophytic Methylobacterium affects nutrient uptake and growth of pine seedlings in vitro
Cycads make their own fertilizer. Every living cycad gets nitrogen from bacteria living in special coral-shaped roots.44PubMed. Nitrogen isotopes reveal independent origins of N(2)-fixing symbiosis in extant cycad lineages Most microbes in those roots can turn nitrogen from the air into plant food.45PubMed Central. Cycad Coralloid Roots Contain Bacterial Communities Including Cyanobacteria and Caulobacter spp. That Encode Niche-Specific Biosynthetic Gene Clusters
In a garden, you can protect these partnerships by avoiding heavy fertilizer, which can reduce the root fungi, and by leaving needle litter in place and not compacting the soil. If you grow a cycad, the coral-like knobs at its root crown are healthy, not disease.
Welwitschia and Desert Extremes
Welwitschia grows in the Namib desert yet loses a lot of water through its leaves around midday.46South African Journal of Botany. Ecophysiological studies on Welwitschia mirabilis in the Namib desert Its roots reach soil water other plants cannot use.47Advances in Botanical Research. Welwitschia mirabilis—New Aspects in the Biology of an Old Plant It can therefore afford to sweat water, which keeps its large leaves from overheating.48Advances in Botanical Research. Welwitschia mirabilis—New Aspects in the Biology of an Old Plant It feeds by ordinary daytime photosynthesis rather than the night-time system of cacti.49South African Journal of Botany. Ecophysiological studies on Welwitschia mirabilis in the Namib desert
The plant itself looks odd. It has only two strap-shaped leaves, which grow for its whole life. Wind frays and splits them so the plant looks like it has many. Some plants are thought to be over a thousand years old.
Giant Genomes and Deep History
The seed itself first appeared in the late Devonian, around 360 million years ago.50PubMed Central. Early evolutionary history of the seed Fire-adapted traits in conifers trace back about 350 million years.51Journal of Ecology. A 350‐million‐year legacy of fire adaptation among conifers Gymnosperms dominated dry lands before flowering plants rose.52Palaeogeography, Palaeoclimatology, Palaeoecology. An herbaceous fossil conifer: Gymnospermous ruderals in the evolution of Mesozoic vegetation
Many conifer genomes are over 10 billion DNA letters, several times the human genome.53PubMed Central. Evolution of complex genome architecture in gymnosperms Repeated “jumping gene” segments have piled up over millions of years.54PubMed Central. Novel Insights into Plant Genome Evolution and Adaptation as Revealed through Transposable Elements and Non-Coding RNAs in Conifers The plants remove this extra DNA very slowly.55PubMed. A chromosome-level genome assembly of Platycladus orientalis and comparative genomics reveal pivotal roles of transposable elements in gene duplication and pseudogenization across gymnosperm giga-genomes The size has practical consequences: it made conifer genetics slow to study and makes breeding improved trees harder.
Threats and Uses Today
70% of forest species worldwide work close to the drought level that blocks their wood.56PubMed. Global convergence in the vulnerability of forests to drought Even wet forests face drought-driven die-off.57PubMed. Global convergence in the vulnerability of forests to drought Most gymnosperm habitats in China will face more climate swings, worsening some species’ threat status.58PubMed Central. Spatiotemporal Distribution Patterns and Conservation Priorities of Gymnosperms With Different Leaf Shapes in China Under Climate Change
People rely on these plants in many ways. The yew-derived cancer drug Taxol is itself a treatment and also led to two related approved medicines.59PubMed Central. Nature as a Remarkable Chemist: A Personal Story of the Discovery and Development of Taxol® Docetaxel treats breast cancer, and cabazitaxel treats advanced prostate cancer.60PubMed Central. Nature as a Remarkable Chemist: A Personal Story of the Discovery and Development of Taxol®
Closer to home, most construction lumber and paper comes from conifers. Pine nuts are seeds, juniper berries flavor gin, and turpentine comes from pine resin.