Botany Terms Starting With G
Botany Glossary: G
Gametophyte
/ gah-MEE-toh-fyt / · Greek gametes, spouse; phyton, plant
Gametophyte is the haploid, multicellular phase of a plant's life cycle that produces gametes by mitosis, alternating with the diploid sporophyte generation.
In bryophytes such as mosses, the gametophyte is the dominant, conspicuous generation, consisting of leafy shoots 1 to 10 centimeters tall that photosynthesize and bear antheridia and archegonia. Ferns produce heart-shaped prothallus gametophytes 5 to 10 millimeters across on moist soil, each bearing both male and female sex organs on the same thallus. In flowering plants, the gametophyte is microscopic: the male gametophyte within a pollen grain comprises just two or three cells totaling less than 100 micrometers in diameter, while the female gametophyte within the ovule consists of seven cells arranged in a precise pattern.
This dramatic reduction in gametophyte size across land plant lineages reflects a long evolutionary trend toward sporophyte dominance.
The female gametophyte of flowering plants, called the embryo sac, typically contains eight nuclei arranged in seven cells, including the egg cell and two polar nuclei that together participate in double fertilization, a process unique to angiosperms.
Gametophytes are always large, leafy plants. In seed plants they are microscopic structures hidden inside pollen grains or ovules and never live independently.
In the common haircap moss (Polytrichum commune), the leafy green plant that carpets forest floors is the gametophyte generation. This structure can grow up to 40 centimeters tall and lives for several years, producing sperm and eggs at its tips. The sporophyte, by contrast, is a short-lived stalk that depends on the gametophyte for water and nutrients.
Gamopetalous
/ gam-oh-PET-uh-lus / · Greek gamos (union) + petalon (leaf, petal)
Gamopetalous describes a flower whose petals are fused, either at the base or along most of their length, forming a single corolla unit such as a tube, bell, or funnel.
Gamopetalous flowers have petals fused into tubes, bells, or funnel shapes that range from barely connate at the base to deeply tubular with flared limbs. Morning glory flowers form a single funnel-shaped corolla from five fused petals, creating a continuous structure rather than separate parts. Tobacco plants (Nicotiana tabacum) in the family Solanaceae develop narrow floral tubes up to 8 centimeters long that suit long-tongued hawkmoths, which are the primary pollinators.
Degree of fusion directly affects nectar access, restricting entry to pollinators with sufficient tongue or bill length and thereby promoting specialization between flower and pollinator.
Petal fusion has evolved independently in many unrelated plant families, a pattern botanists call convergent evolution. In the family Convolvulaceae alone, which includes morning glories, all roughly 1,900 species share the gamopetalous condition despite occupying habitats from tropical forests to temperate roadsides.
Gamopetalous flowers have no petals. They have petals that are fused together into a single corolla unit rather than remaining separate.
In the common foxglove (Digitalis purpurea), the five petals are fused into a tubular corolla roughly 4 to 5 centimeters long. Bumblebees, which have bodies long enough to reach the nectar at the tube's base, are the primary pollinators. This tight fit between tube length and pollinator body size illustrates how the gamopetalous condition can drive pollinator specificity.
Japanese Morning Glory →Germination
/ jer-mih-NAY-shun / · Latin germinare (to sprout)
Germination is the resumption of active growth by a viable seed after a period of dormancy, beginning with water uptake and culminating in emergence of the embryonic root and shoot.
Germination begins with imbibition, the rapid uptake of water that rehydrates dry seed contents and reactivates metabolic enzymes. Swelling pressure from imbibition can exceed 1,000 kilopascals, sufficient to rupture the seed coat and allow radicle emergence. Wheat (Triticum aestivum) seeds germinate within 48 hours of reaching adequate soil moisture at temperatures between 12 and 25 degrees Celsius, with the radicle anchoring the seedling before the coleoptile pushes upward through the soil.
Light, temperature, and the balance between gibberellins and abscisic acid all regulate whether dormancy breaks, ensuring germination occurs under conditions favorable for seedling survival.
Some seeds require specific environmental cues before germination can proceed. Seeds of the smoke bush (Ceanothus species) germinate only after exposure to chemicals in wildfire smoke, a response that synchronizes seedling establishment with the nutrient-rich, competitor-free conditions that follow a burn.
Germination starts when leaves appear above the soil. Germination begins underground when the seed resumes metabolic activity and the radicle emerges, well before any leaf reaches the surface.
In radish (Raphanus sativus) seeds sown in moist soil at 20 degrees Celsius, the radicle typically emerges within 3 to 4 days. The root tip elongates at roughly 1 centimeter per day during early establishment, anchoring the seedling and beginning mineral uptake before the hypocotyl arches above the soil surface.
Gibberellin
/ jib-er-EL-in / · Gibberella fujikuroi (the fungus it was first found in)
Gibberellin is a class of diterpenoid plant hormones that promote stem elongation, seed germination, and fruit development by stimulating cell division and elongation in target tissues.
Gibberellins are synthesized primarily in young leaves, developing seeds, and root tips, then transported through the phloem and xylem to target tissues throughout the plant. Their most dramatic effect is stem elongation: gibberellins trigger degradation of DELLA proteins, which normally suppress growth genes, causing internodal cells to divide and elongate rapidly. More than 130 structurally distinct gibberellins have been identified across plants and fungi, though only a few, particularly GA1 and GA3, show strong biological activity in most species.
Farmers apply gibberellin sprays to Thompson Seedless grapes to increase berry size by up to 50 percent and to malting barley to accelerate uniform germination before brewing.
Gibberellins were first identified not in a plant but in the fungus Gibberella fujikuroi, which causes "foolish seedling disease" in rice. Japanese plant pathologist Eiichi Kurosawa demonstrated in 1926 that a secretion from this fungus caused rice seedlings to grow abnormally tall, leading to the isolation of gibberellic acid in the 1950s.
Mycology →Gibberellin only affects plant height. Gibberellins also regulate seed dormancy, the transition to flowering in long-day plants, sex determination in cucumbers, and fruit set without fertilization.
In dwarf pea plants (Pisum sativum) carrying the le mutation, which blocks a step in gibberellin biosynthesis, stems remain roughly half the height of wild-type plants. Applying as little as 0.1 micrograms of GA1 per plant restores near-normal internode length within days, demonstrating how precisely gibberellin concentration controls elongation.
Glandular Trichome
/ GLAN-joo-ler TRY-kohm / · Scientific term used in plant anatomy.
Glandular trichome is a hair-like epidermal outgrowth on a plant surface that synthesizes and secretes chemical compounds, including volatile oils, resins, and defensive alkaloids, from a specialized secretory head.
Glandular trichomes consist of a multicellular stalk topped by one or more secretory head cells that accumulate products in a subcuticular storage cavity before releasing them. In peppermint (Mentha x piperita), peltate glandular trichomes store menthol and limonene in concentrations that can comprise 0.5 to 3 percent of leaf dry weight. Some carnivorous plants, including sundews (Drosera species), use glandular trichomes to secrete both adhesive mucilage that traps insects and digestive enzymes that break down captured prey.
Trichome density varies widely across species: cannabis (Cannabis sativa) leaves can bear more than 600 trichomes per square millimeter, each producing tetrahydrocannabinol and related cannabinoids that deter herbivores.
Wild tobacco (Nicotiana attenuata) adjusts glandular trichome density in response to herbivore attack. Plants damaged by tobacco hornworm caterpillars (Manduca sexta) increase trichome secretion of diterpene glycosides within 24 hours, reducing caterpillar feeding rates by more than 60 percent in controlled experiments.
Glandular trichomes protect plants only by being physically sharp or sticky. Many glandular trichomes on smooth-feeling leaves deter herbivores and pathogens entirely through toxic or repellent chemistry, with no mechanical barrier involved.
In tomato plants (Solanum lycopersicum), type VI glandular trichomes on leaf surfaces secrete methylketones and sesquiterpenes that repel aphids and whiteflies. These trichomes are most dense on young leaves, where roughly 400 per square centimeter have been counted, providing the greatest chemical defense where tissue is most vulnerable to insect damage.
Peppermint Flowers →Guard Cell
/ GARD SEL / · Old French garder (to guard) + Latin cella (small room)
Guard cell is one of a pair of specialized, chloroplast-containing epidermal cells that flank a stomatal pore and regulate its opening and closing by changing shape in response to turgor pressure.
Guard cells control stomatal aperture by accumulating potassium ions, which draws water in by osmosis, increasing turgor and bowing the cells outward to open the pore. Stomata in most plants open during daylight when photosynthesis demands carbon dioxide and close at night or under drought stress to limit water loss. A single square centimeter of a sunflower (Helianthus annuus) leaf surface contains roughly 160 stomata on the lower epidermis, each flanked by a pair of guard cells.
Unlike other epidermal cells, guard cells retain functional chloroplasts that contribute to the ATP and sugar signals driving ion uptake, linking stomatal opening directly to photosynthetic activity.
In the succulent plant family Crassulaceae, guard cells follow a reversed daily rhythm: stomata open at night to take in carbon dioxide, which is stored as malic acid, and close during the day to prevent water loss. This crassulacean acid metabolism strategy lets plants such as jade plant (Crassula ovata) thrive in arid environments where daytime stomatal opening would be lethal.
Guard cells are holes in the leaf surface. Guard cells are living, metabolically active cells that surround and control the stomatal pore; the pore itself is simply the gap between them.
In broad bean (Vicia faba) leaves, guard cells swell from roughly 5 micrometers to 15 micrometers in width as potassium ions accumulate during the morning hours. This turgor-driven shape change widens the stomatal pore from nearly closed to a maximum aperture of about 10 micrometers, increasing carbon dioxide diffusion into the leaf by an order of magnitude compared with closed stomata.
Gymnosperm
/ JIM-noh-sperm / · Greek gymnos (naked) + sperma (seed)
Gymnosperm is a seed-bearing vascular plant whose seeds develop exposed on the surface of a cone scale or similar structure rather than enclosed within an ovary.
Gymnosperms comprise four living lineages: conifers (Coniferophyta), cycads (Cycadophyta), ginkgo (Ginkgophyta), and gnetophytes (Gnetophyta), totaling roughly 1,000 extant species. Conifers alone dominate boreal forests across North America and Eurasia, with species such as Scots pine (Pinus sylvestris) forming continuous canopy over millions of hectares. Pollen in most gymnosperms is wind-dispersed and produced in enormous quantities; a single male cone of eastern white pine (Pinus strobus) releases approximately 1 million pollen grains during a single season.
Unlike angiosperms, gymnosperms lack a closed carpel, so fertilization occurs directly on the exposed ovule surface after pollen lands on a pollination droplet secreted by the ovule.
The maidenhair tree (Ginkgo biloba) is the sole surviving species of its entire division, Ginkgophyta, making it a living fossil with no close living relatives. Fossil ginkgo leaves virtually identical to those of living trees appear in Triassic deposits roughly 200 million years old, a span of morphological stability unmatched among seed plants.
Gymnosperms have no seeds. Gymnosperms produce seeds, but those seeds are never enclosed within a fruit because the ovule sits exposed on a cone scale rather than inside a closed ovary.
In ponderosa pine (Pinus ponderosa), seeds develop on the upper surface of woody cone scales over a period of about two years following pollination. At maturity, each cone scale bears two winged seeds roughly 6 to 8 millimeters long that are released when the cone opens in dry conditions, allowing wind to carry them up to 100 meters from the parent tree.
Gynoecium
/ jy-NEE-shum / · Greek gyne (woman) + oikos (house)
Gynoecium is the collective term for all the carpels in a single flower, forming the female reproductive unit that contains the ovules and, after fertilization, develops into the fruit.
The gynoecium can consist of a single carpel (monocarpous), multiple separate free carpels (apocarpous), or multiple fused carpels (syncarpous), and each arrangement produces a distinct fruit type. In tulips (Tulipa gesneriana), the gynoecium is syncarpous with three fused carpels forming a single three-chambered ovary containing dozens of ovules. Each carpel contributes a style that conducts pollen tubes from the stigma downward to the ovules, with tube growth rates reaching 1 centimeter per hour in some species.
The number and fusion pattern of carpels determine whether the resulting fruit splits at maturity, how many seeds it contains, and how those seeds are dispersed.
In the buttercup family (Ranunculaceae), most species have an apocarpous gynoecium with numerous free carpels arranged in a spiral on the receptacle. Counting these free carpels is one of the features botanists use to place a flower within this family, and some buttercup species bear more than 30 separate carpels in a single flower.
The gynoecium is the male part of a flower. The gynoecium is the complete female reproductive structure; the male equivalent is the androecium, which comprises the stamens.
In a tulip flower, the gynoecium sits at the center of the perianth and consists of three fused carpels forming a single ovary roughly 1.5 centimeters long. After fertilization, this ovary matures into a dry, three-valved capsule that splits open to release flat, papery seeds dispersed by wind.