Fir trees are monoecious, meaning they have both male and female cones on the same tree.
Dioecious trees have either all male or all female reproductive organs.
Female cones produce ovules.
Pollen needs to reach an ovule for reproduction.
Male cones produce pollen.
Gymnosperms rely on wind to spread pollen and produce large quantities of pollen to increase the chances of successful pollination.
Progymnosperms
Progymnosperms are spore-bearing plants and ancestors to all seed plants.
They first appeared approximately 390 million years ago (MYA).
Archaeopteris were the first large trees during the Devonian period.
They possessed secondary vascular tissue (woody tissue) and fern-like fronds.
Evolutionary Tree
The evolutionary tree includes:
Bryophytes: Mosses, liverworts, and hornworts.
Pteridophytes: Monilophytes and lycophytes.
Spermatophytes: Gymnosperms and angiosperms.
Gymnosperms include extinct gymnosperms and seed ferns.
Angiosperms include monocots, eudicots, and other groups.
Seeds
Seeds are highly resistant structures that protect plant embryos.
They contain a diploid embryo and food storage within a seed coat.
Seeds are found in both gymnosperms and angiosperms.
Male Gametophyte
In seed plants, the male gametophyte is highly reduced and becomes a pollen grain.
The entire gametophyte moves to the female gametophyte via wind or a pollinator.
Water is not required for fertilization.
Female Gametophyte
The female gametophyte has an extra layer of sporophyte tissue around the ovule and contains three parts:
Integument: Derived from the sporophyte, producing the seed coat.
Megasporangium: Forms the nucellus with an opening for the pollen grain (micropyle).
Megaspore: A haploid female spore that develops into the gametophyte.
The embryo develops within the ovule.
Fertilized Female Gametophyte
Forms a zygote from the female egg and male sperm.
The seed enters a dormant stage.
The embryo survives until environmentally favorable conditions are present.
The seed coat is a tough, external layer to protect the embryo.
The cotyledon stores food for embryo development.
Gymnosperms
Gymnosperms are "naked seeds" that develop on the surface of a scale.
There are four groups:
Coniferophytes
Cycadophytes
Gnetophytes
Ginkgophytes
The ovule is not completely encased by sporophyte tissue.
Coniferophytes
Coniferophytes are the largest group of gymnosperms, making up approximately 40% of forests.
Pinus is an ecologically and economically important genus.
Leaves are organized as bundles of needles with thick cuticles and recessed stomata to reduce water loss.
These adaptations are often found in arid or frigid environments where the ground freezes part of the year.
Cuticle: (\text{waxy layer})
Xylem: (\text{vascular tissue})
Phloem: (\text{vascular tissue})
Stoma: (\text{pore for gas exchange})
Pine trees are native to the northern hemisphere but have been planted throughout the southern hemisphere for lumber.
They secrete resins to deter insects and fungi growth, which are used by humans to create:
Turpentine: A solvent used for thinning paints and as a varnish.
Rosin: Used in adhesives, inks, and sealing wax.
Specific Gymnosperm Examples
Sequoia sempervirens (Coastal Redwood) is the world's tallest species, found only in California.
Sequoiadendron giganteum (Giant Sequoia) is the world's largest species, found only in California.
Pinus longaeva (Bristlecone pine) is the world's oldest species, found in California, Nevada, and Utah.
Pinus radiata: Some trees are fire-adapted and their cones only open up and release seeds at high temperatures.
Araucaria
Araucaria was widespread until the end of the Cretaceous period (65 MYA).
Current populations are likely relics of plate tectonics (vicariance).
An example is the Monkey Puzzle Tree.
Pinus Reproduction
Male and female gametes are produced on the same tree on cones.
Male cones produce millions of pollen grains.
Female cones have seeds located on each scale.
Pinus has a haplodiplontic lifecycle.
Female cones contain megasporangia forming the ovule.
A mother cell undergoes meiosis to produce a megaspore.
Microspores and Pollen
Male cones contain microsporangia.
A mother cell within a microsporangium undergoes meiosis to produce microspores.
Pollen grains are dispersed via wind.
Pollen grains have air sacs for buoyancy.
They also have a generative cell.
Pinus Fertilization
Pollen grain enters the ovule via the micropyle, leading to pollen tube formation, which allows sperm and egg to fuse.
Archegonia form near the micropyle within the megaspore.
Sperm are non-motile.
Gnetophytes
Gnetophytes possess xylem vessels, a cell type for efficient transport of water and nutrients throughout the plant, which is similar to angiosperms but likely the result of homoplasy.
Examples include Welwitschia sp. and Ephedra sp.
Cycadophytes
Cycadophytes superficially resemble palm trees but produce cones.
Cycads are dioecious, with male and female cones produced on separate plants.
Cycadophyte reproduction system is similar to pines, but sperm are flagellated, which does not require water due to transport via pollen grain.
Ginkgo biloba
Ginkgo biloba is the only single living species of Ginkgophyte.
The plant is dioecious.
Male cones are used as an ornamental plant.
Female sarcotesta produces butyric acid and smells like rancid butter.
The fleshy sarcotesta is derived from the seed coat and is not considered a fruit.
It has flagellated sperm.
Gymnosperm Relationships
Gymnosperms form a monophyletic group.
Ginkgophytes and Cycadophytes are sister taxa at the base of gymnosperms.