Seeded Plants: Gymnosperms

Overview of Gymnosperms

Overview of Gymnosperms

• Latin "Gymno - sperms" = naked seed
• Dominant producers on land
• Dominant Form: Sporophyte
• Same as seedless vascular plants
• Opposite of non-vascular plants
• Evolution of Pollen and Seeds
• Gametophyte dependent on Sporophyte
• Pollen: male gametophyte protected by pollen grain
• Ovule: female gametophyte, immobile
• Seeds: fertilized ovule (diploid, next generation sporophyte)
• Male Gametophyte
• Microsporangium (2N) => Microspore (1N) => Male Gametophyte (1N; pollen grains)
• Pollen tube: extends from the pollen grain to reach the egg
• Pollen: tough sporopollenin coating, protects from damage, drying and UV
• Female Gametophyte
• Ovule: Integuments + Megasporangium + Megaspore
• Integument: protective outer layer
• Megasporangium (2N) => megaspore (1N)
• Seed: Protected embryo
• Gametophyte tissue protected by parental sporophyte tissue
• Size varies

Gymnosperm Reproduction

• Pollination: when pollen meets ovule
• Major adaptation
• Before seeds: sperm needed to swim through water
• Dispersal stage: spore
• With seeds: sperm is protected in pollen grain
• Dispersal stage: seed, can travel long distances (wind or animals)
• Food for seed comes from gametophyte
• Seed Germination
• Some seeds need special conditions
• Fire/smoke
• Last frost (end of winter)
• Digestion (animal transport)
• Larger seeds: more energy stored, needs less sun
• Smaller seeds: less energy stored, needs more sun

Diversity of Gymnosperms

Four extant phyla

Ginkgophyta

• Single living species
• Ginkgo biloba
• Used as herbal medicine and tea

Cycadophyta

• Abundant and diverse during Mesozoic
• ~130 species left in tropics
• Large cones and palm-like leaves
• Insect pollinated Example: beetles
• Small, fragmented distribution

Gnetophyta

• Harsh environments Example: desert
• Diverse
• Grouped by DNA evidence

Coniferophyta

• Characterized by shape of leaf
• Scale-like Example: Junipers
• Long Needles
• Flat Leaves Example: Monkey-puzzle Tree
• Abundant in boreal and alpine regions
• Waxy coat and permanent leaves = cold and dry adapted
• Evergreen: do not loose leaves in winter