It is commonly found along streams and lakes as well as in Adirondack swamps. Despite its name, it is not a true cedar but rather a cypress — in the Cupressaceae family.
Its leaves are flattened and scale-like, and its bark is reddish-brown with a shredded texture. Red pine Pinus resinosa is a member of the family Pinaceae found in relatively poor, sandy soils. It can grow to 50—80 feet and live for over years. It has needles 4—6 inches long in clusters of two. Its bark is typically orange-brown and gradually becomes gray-brown with shallow fissures and broad flat ridges toward the base of older trees.
Red pine is often used in reforestation and sometimes as an ornamental. White pine Pinus strobus , in the family Pinaceae, is a generalist found in the Northeast, including the Adirondacks.
This is the tallest conifer, growing to feet or more. Most gnetophytes are stem plants, like Ephedra, branched photosynthetic stems with no leaves.
Gnetum has leaves like those of modern flowers. But the third genus, Welwitschia , is one of the strangest plants on earth. Welwitschia really looks like something out a science fiction novel. It grows in the deserts of southwestern Africa. Most of the plant is deep underground, with a root stretching down to the water table. The top appears above the soil as a squat cup- shaped stem with two strap-shaped leaves.
These are the only leaves the plant will ever grow, and they may live a hundred years or more and reach several meters, usually torn into strips.
Male or female strobili grow from the margins of the upper stem. Division Coniferophyta - sp. The conifers are the largest and most successful group of living gymnosperms. Many of our familiar forest trees are conifers, including pines, spruces, firs, hemlocks, yews, redwoods and cypress trees.
They are an ancient group, dating back mya. They evolved during the Permian, toward the end of the Paleozoic, at a time when the climate was very cool and dry. Their special water conducting cells, called tracheids, allowed them to thrive in these climates and these same adaptations let them continue to dominate in colder and dryer environments today, such as northern latitudes, mountain slopes, and sandy soils.
Because they are superior competitors in such habitats even today, they are the only Division of gymnosperms to successfully compete with the flowering plants. Most conifers are evergreens, with the larch and the bald cypress being notable exceptions. Their needle-shaped leaves are also an adaptation to conserve water. Needles usually occur in small bundles, each bundle emerging from a base that is actually a greatly truncated branch.
Conifers have tremendous economic importance, as a source of timber and for byproducts such as pitch, tar, turpentine, and amber and other resins.
Millions are sold each year as Christmas trees. All conifers produce cone shaped strobili, both male cones often called pollen cones and female cones often called seed cones or ovulate cones. Both male and female cones are usually produced on the same tree, but not at the same time, so the trees do not fertilize themselves.
Female cones are large and conspicuous, with thick woody scales. Seed cones can persist on the tree for several years after fertilization. A few species, like junipers and the locally common podocarpus front of Richardson , have seeds that are covered with a fleshy coating, and resemble small berries.
The sporangia produced by the sporophytes are located at the bases of the sporophylls, and collected in the strobilus we call a pine cone. The microspore mother cell in the microsporangia produces the haploid pollen grains. Each scale or sporophyll in the male cone has two microsporangia on its lower surface. Each pollen grain consists of only four cells. When the immature pollen grain finally reaches the seed cone, the megaspore mother cell in the megasporangium produces four haploid megaspores.
Three of these megaspores degenerate, and only the fourth germinates into the female gametophyte. The female gametophyte consists of two or more archegonia, with a single egg in each one. All eggs are usually fertilized. Each visible scale in the seed cone is really a much reduced lateral branch in itself. So each scale is homologous with the entire male cone. The megasporangium, which is called a nucellus in seed plants, is covered with a layer of protective cells called an integument, which is open at one end.
This tiny opening, the micropyle, marks the point where the male pollen tube will grow into the megasporangium. The megasporangium, together with its integument, makes up the ovule. Seeds develop from ovules. Each scale in the seed cone has two ovules on the upper surface of the scale, and so will ultimately bear two seeds side by side. The pollen grains formed in the microsporangia of pines have tiny wing on either side. Because they are wind-pollinated?
The ovulate cones open to receive pollen, then may close again to protect the developing embryos. When pollen grains land on the ovulate cones, they grow a long pollen tube. By the time this tube reaches the archegonia, about 15 months after pollination, the male gametophyte is fully mature. The pollen tube enters through the micropyle.
The sperm nucleus divides in two, and the pollen tube discharges two sperm. One sperm nucleus degenerates, the other fertilizes the egg. It takes the female gametophyte about 15 months to mature, and about the same time for the pollen tube of the male gametophyte to reach it. The seed develops within the megasporangium. The seed is the structure containing the embryonic plant and the stored nutrition to support it. A section of the surface of the scale usually detaches along with the seed, giving the seed a little wing to help disperse it farther from the tree.
Conifer seeds are very complex little structures, containing cells from three generations of the tree.
The nutritive tissues inside the seed are actually the haploid body cells of the female gametophyte. The seed also contains the developing diploid sporophyte, the little embryonic conifer.
The outer wrapping of the seed, the tough and protective seed coat, is formed from the diploid cells of the parent sporophyte. Pine seeds, along with acorns, are the most important source of plant food for North American wildlife. Examine the cycads and cycad frond on display.
How do the leaves of cycads differ from those of angiosperms? Cycad leaves are full of potent neurotoxins, carcinogens, and other toxic chemicals? Cycads are protected in another way, as you know if you've bumped into one of the many cycads on campus.
Why evolve such potent defenses? Examine the ginkgo leaves and seeds. You might detect a faint odor, a reminder of the very nasty smell these seeds make when their fleshy covering starts to rot. The delicate appearance of the leaves gives the ginkgo its common name, the maidenhair tree. Where can we find these trees on campus? Note the difference between the fleshy-covered seeds of Ginkgo and Podocarpus , and the dry seeds of Pinus.
What function would this fleshy covering have served? The answer to this question may also explain why ginkgo seeds really stink. Compare Ephedra to the other gymnosperms. Until recently, we thought that this curious "stem plant" was closely related to flowering plants. Angiosperms have developed flowers and fruit as ways to attract pollinators and protect their seeds, respectively. Flowers have a wide array of colors, shapes, and smells, all of which are for the purpose of attracting pollinators.
Once the egg is fertilized, it grows into a seed that is protected by a fleshy fruit. As angiosperms evolved in the Cretaceous period, many modern groups of insects also appeared, including pollinating insects that drove the evolution of angiosperms; in many instances, flowers and their pollinators have coevolved. Angiosperms did not evolve from gymnosperms, but instead evolved in parallel with the gymnosperms; however, it is unclear as to what type of plant actually gave rise to angiosperms.
Key Terms clade : a group of animals or other organisms derived from a common ancestor species angiosperm : a plant whose ovules are enclosed in an ovary basal angiosperm : the first flowering plants to diverge from the ancestral angiosperm, including a single species of shrub from New Caledonia, water lilies and some other aquatic plants, and woody aromatic plants.
Evolution of Angiosperms Undisputed fossil records place the massive appearance and diversification of angiosperms in the middle to late Mesozoic era. A large number of pollinating insects also appeared during this same time. Flowers and Fruits as an Evolutionary Adaptation Angiosperms produce their gametes in separate organs, which are usually housed in a flower. It often has features considered attractive to its particular pollinator. Provided by : Boundless.
Provided by : Wiktionary. Angiosperms produce their gametes in separate organs, which are usually housed in a flower. Both fertilization and embryo development take place inside an anatomical structure that provides a stable system of sexual reproduction largely sheltered from environmental fluctuations. Flowering plants are the most diverse phylum on Earth after insects; flowers come in a bewildering array of sizes, shapes, colors, smells, and arrangements. Most flowers have a mutualistic pollinator, with the distinctive features of flowers reflecting the nature of the pollination agent.
The relationship between pollinator and flower characteristics is one of the great examples of coevolution. Coevolution of flowers and pollinators : Many flowers have coevolved with particular pollinators, such that the flower is uniquely structured for the mouthparts of the pollinator.
It often has features considered attractive to its particular pollinator. Following fertilization of the egg, the ovule grows into a seed. The surrounding tissues of the ovary thicken, developing into a fruit that will protect the seed and often ensure its dispersal over a wide geographic range.
Tomatoes, walnut shells and avocados are all examples of fruit. As with pollen and seeds, fruits also act as agents of dispersal. Some may be carried away by the wind. Many attract animals that will eat the fruit and pass the seeds through their digestive systems, then deposit the seeds in another location. Cockleburs are covered with stiff, hooked spines that can hook into fur or clothing and hitch a ride on an animal for long distances.
The cockleburs that clung to the velvet trousers of an enterprising Swiss hiker, George de Mestral, inspired his invention of the loop and hook fastener he named Velcro. Privacy Policy. Skip to main content. Seed Plants. Search for:. Evolution of Seed Plants. The Evolution of Seed Plants and Adaptations for Land The evolution of seeds allowed plants to reproduce independently of water; pollen allows them to disperse their gametes great distances.
Learning Objectives Recognize the significance of seed plant evolution. Key Takeaways Key Points Plants are used for food, textiles, medicines, building materials, and many other products that are important to humans. The evolution of seeds allowed plants to decrease their dependency upon water for reproduction. Seeds contain an embryo that can remain dormant until conditions are favorable when it grows into a diploid sporophyte.
Seeds are transported by the wind, water, or by animals to encourage reproduction and reduce competition with the parent plant.
0コメント