The gymnosperms are a paraphyletic group according to the "anthophyte" hypothesis.
Some descendants of a single common ancestor are not included in paraphyletic groups.
The gymnosperms are sister to the conifers, according to the "netifer" hypothesis.
These relationships may be clarified by further studies.
The gymnosperms include naked seeds, separate female and male gamtophytes, pollination by wind and insects, and ovulate cones.
Some seeds are covered by sporophyte tissues.
Gymnosperms were the dominant species.
They are adapted to live in areas with little or no fresh water during a part of the year.
The evergreen conifers have a good advantage in cold and dry weather in the taiga.
conifers are ready to take advantage of the first sunny days of spring because of low levels of photosynthesis during the cold months.
Most conifers don't lose their leaves all at once so they are more vulnerable to leaf invasion.
They can't shed parasites and restart with a fresh supply of leaves.
The life cycle of a gymnosperm consists of generations with a dominant sporophyte that reduces male and female gametophytes.
Gymnosperms are Heterosporous.
The male and female reproductive organs can be found in cones.
Gymnosperms have a life cycle that serves as an example of reproduction.
Pine trees are conifers and carry both male and female sporophylls.
They are monoecious plants.
Like all gymnosperms, pines are Heterosporous and produce two different types of spores.
There are small male cones and large female cones in the strobili.
A few haploid cells are enclosed in a tough wall.
The yellow pollen is carried by the wind in the spring.
A gametophytes will land on a female cone.
The initiation of pollen tube growth is called pollination.
The pollen tube develops slowly, and the generative cell in the pollen grain produces two haploid sperm or generative nuclei.
The haploid nucleus of an egg cell will unite with the haploid sperm nucleus at fertilization.
Each ovule has a narrow passage that leads to the base of the sporophyll.
A pollen tube will grow through this passage.
A female multicellular gametophyte is formed when three of the four cells break down.
A sticky pollination drop traps windblown pollen grains near the opening of the micropyle as the female gametophyte begins to develop.
A pollen tube is formed.
As the egg matures, one of the generative sperm nuclei from the pollen tube will enter the egg and join the egg nucleus.
The embryo is enclosed in a seed coat of tissue from the parent plant after fertilization.
Although several eggs may be formed and even fertilized, there is usually a single embryo in each ovule.
Fertilization and seed development in pine trees can take up to two years after pollination.
The life cycle of a conifer is shown in Figure 26.8 The longest phase of a gymnosperm is the sporophyte (2n) phase.
The gametophytes are reduced in size.
It may take more than a year between pollination and fertilization for the female gametophyte to form.
The female gametophyte can produce eggs when the pollen tube is slow.
The life cycle of a conifer is shown in this image.
Female cones are fertilized by male cones blowing up into upper branches.
The megaspore shown in the image develops into the female gametophyte as the pollen tube slowly grows toward it, eventually fusing with the egg and delivering a male nucleus, which combines with the female nucleus of the mature egg.
The process of seed production in gymnosperms is shown in this video.
Gymnosperms are classified into four categories.
The pattern of seed development and production of secondary cambium is similar to that of Coniferophyta, Cycadophyta, and Ginkgophyta.
The closest group to angiosperms is Gnetophyta, because they produce true xylem tissue with vessels as well as the tracheids found in the rest of the gymnosperms.
conifers are trees that are tall and have leaves.
The leaves have a thick cuticle and narrow shape.
Snow slides off leaves, keeping the snow load light and reducing broken branches.
The predominance of conifers in cold climates is due to their ability to adapt to cold and dry weather.
pines, firs, cedars, sequoias, and yews are evergreen trees.
Some species lose leaves in the fall.
The bald cypress is one of the examples of deciduous conifers.
Many trees are cut down to make paper and timber.
The dominant form of vegetation at high altitudes is cattle.
There are four plants in this picture: evergreen spruce Picea sp., juniper Juniperus sp., coastal redwood or sequoia Sequoia sempervirens, and the tamarack Larix larcinia.
It is unusual for a gymnosperm to be pollinated by beetles rather than wind.
During the age of dinosaurs, large cycads dominated the landscape, but only a hundred or so smaller species persisted to modern times.
Several species are protected through international conventions.
They are used as ornamental plants in the tropics and subtropics because of their attractive shape.
The cycad, Encephalartos ferox, has large cones and broad leaves.
The leaves are fan-shaped and turn yellow in autumn and fall from the tree.
The preservation of G. biloba was ensured by Chinese Buddhist monks.
It is resistant to pollution and is planted in public spaces.
Plants produce male and female organs.
Gardeners usually plant male trees because the seeds produced by the female plant have an off-putting smell.
The leaves and fruit of Ginkgo biloba are depicted in a plate from a 1870 book.
Their possession of vessel elements suggests they are close to modern angiosperms.
The three living genera are quite different, which may mean that the group is not monophyletic.