By the end of the Paleozoic, a new group of plants was challenging the million-year domination of the ferns and fern allies. The seed plants protected the embryonic sporophyte from drying up by encasing it in a tough waterproof seed coat. The evolution of the seed is as profound a step as the evolution of the shelled egg in reptiles.
Just as the evolution of the amniotic egg enabled reptiles to become the first truly terrestrial vertebrates, to break that final link with their aquatic heritage, so did the evolution of the seed allow plants to escape the limitation of growing in very moist environments. These gymnosperms soon became the dominant plants.
The Mesozoic is sometimes called the Age of Cycads. But their success was short-lived. During the mid to late Mesozoic, the first flowering plants or angiosperms appeared. They rapidly dominated the more primitive gymnosperms, and are the dominant plants on Earth today. These waves of competition are typical of the history of life. The survivors are relegated to scattered populations in restricted habitats, where they live in the shadows of their successful competitors.
Among the gymnosperms, only the conifers are major competitors with flowering plants. Having evolved in a dryer, cooler climate, conifers are better adapted to dry or cool habitats, and dominate forests in northern latitudes, at high elevations, and on sandy soils.
Today we will examine both gymnosperms and angiosperms, and compare their complex life cycles. The trend toward a dominant sporophyte stage is now complete. The gametophytes of seed plants are microscopic. The female gametophyte consists of a handful of cells buried in the tissues of the sporophyte. The male gametophyte, the pollen grain , has a brief free-living stage while it is carried from plant to plant by wind, water, or animals.
No longer relying on flagellated sperm, and with their developing embryos protected from desiccation, seed plants break the last link with their aquatic ancestors. The first seed plants evolved relatively early on, in the late Devonian.
By the end of the Paleozoic they were competitive enough to replace the club mosses, horsetails, and whisk ferns, and become the dominant vegetation of the Mesozoic, the era of the dinosaurs. By the end of the Mesozoic, they too would be swept aside by the newly evolved angiosperms, the flowering plants.
There are only living species of gymnosperms, a pale remnant of a once diverse and dominant race. Living gymnosperms are a diverse group of plants, most of which bear their sporangia in large, prominent strobili or cones. These strobili are similar to those of lycopsids and horsetails. Strobili consist of a shortened stem with several modified leaves sporophylls that bear sporangia.
Like all seed plants, gymnosperms are heterosporous. The sporangia that generate the male microspores and female megaspores are usually borne on separate cones. Male cones staminate cones are typically much smaller than female cones ovulate cones. Sporophylls that bear microsporangia are called microsporophylls. Sporophylls that bear macrosporangia are called macrosporophylls.
The pine life cycle is typical of gymnosperms, and is described in detail below. Cycads have very thick leaves, that look like very tough versions of fern fronds. These palm-like plants have unbranched stems, with a terminal crown of leaves. These leaves are incredibly well defended with sharp tips and with complex secondary compounds, including potent neurotoxins and carcinogenic compounds. They reached their peak during the Mesozoic, with species reaching from feet.
A giant cycad today might reach feet max. They are unisexual or dioecious, having separate male and female plants. Dioecious means two houses, vs. Only one genus of cycad Zamia is native to North America.
The Seminoles ate the starchy roots of Zamia pumila , found in southern Florida. In India, Japan, and Sri Lanka, sago flour is often made from cycad stems it is also made from real palms, which are angiosperms. Cycads are widely grown as ornamental landscape plants. Cycads also enrich the fertility of barren soil, because they are symbiotic with nitrogen-fixing cyanobacteria. Cycads are extremely slow growing, and can live 1, years or more. They are wind pollinated, a strategy which requires immense amounts of airborne pollen.
A few may have been pollinated by beetles attracted to the edible pollen grains. This may be the humble beginnings of the complex animal pollination developed by flowering plants. The pollen sacs and ovules are born on scalelike sporophylls in compact cones. Unlike pine cones, the cones of cycads are often very large in relation to the plant. Ginkgo trees are commonly seen in cities today. They are attractive shade trees, reaching feet or more, with beautiful yellow foliage in the Fall.
They are very resistant to air pollution and insects. That the sole remaining species did not join its brethren in extinction we owe to the ancient Chinese and Japanese, who cultivated it in their temple gardens for centuries. Their may no longer be a single living wild tree. It is a popular tree for bonsai, because the leaves will readily miniaturize, and the branches are easy to shape.
The species name biloba comes from the two distinct lobes of its fan-shaped leaves, very different from the straplike or needle shaped leaves of other gymnosperms. The common name maidenhair tree comes from the similarity of ginkgo leaves to fronds of the maidenhair fern.
Ginkgos and cycads show a transitional stage between the primitive ferns and the more advanced conifers and flowering plants. They have flagellated sperm, but the male gametophyte grows a pollen tube, a long filament through which the sperm can safely swim to the egg.
The pollen grains of other seed plants grow similar tubes. The megasporangia, which contains the eggs, form tiny female strobili on the tips of special branches on the female tree. The microsporangia, which produce the pollen grains, are in male strobili that hang down like little pine cones on the male tree.
The seed that forms on the female trees is covered with a thick fleshy coat which makes the seed look like a little fruit which it is technically not. So be very careful if you plant one of these wonderful trees and select a male tree!!
Although in fairness to the female tree, its seed is prized in China as a source of medicinal drugs. This odd little group of gymnosperms are mainly xerophytes, plants that are adapted to dry conditions. They share a close common ancestor with flowering plants. Each genera has some species that produce nectar, and attract insects. It was recently discovered that double fertilization, a trait we thought was unique to flowering plants, also occurs in Ephedra , one of the three surviving genera of gnetophytes.
Ephedra , incidentally is the natural source of the alkaloid ephedrin, used to treat hay fever, sinus headaches, and asthma. Its medicinal properties have been known for at least 5, years! 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. Bare, not enclosed; found on scales, leaves or as cones. Mostly rely on wind. Uses Medications , food, clothing, etc Paper, Lumber , etc Diversity Hundreds of millions of years ago, gymnosperms were the only kind of plant life on Earth. Examples of Angiosperms and Gymnosperms Examples of angiosperms are monocots like lilies, orchids, agaves known for agave nectar and grasses; and dicots like roses, peas, sunflowers, oaks and maples.
Gymnosperm examples include non-flowering evergreen trees such as pine, spruce and fir. Follow Share Cite Authors.
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Anonymous comments 4 March 31, , pm Waw thankz alotz. U guys saved me — Especially the graph, it helped a lot- Thanks — I hate science though this website save me from the teacher — Related Comparisons. Contribute to Diffen Edit or create new comparisons in your area of expertise. Log in ». Beyond the development of flowers and fruits, they also established more advance methods to transport water and sugars within their vascular tissue as well as other improvements in physiology that gave them an advantage over gymnosperms.
The biggest difference between gymnosperm and angiosperms lies in their seeds. In angiosperms, individual flowers can be unisexual, with separate male and female flower structures, or bisexual with both male and female parts on the same flower. While both groups use pollen in reproduction, angiosperms have developed an incredible diversity of strategies for pollen dispersal and, in combination with their insect friends from the animal kingdom, have went on to expand into the most diverse group of plants on earth.
Photo Caption: Gymnosperms, like this Colorado blue spruce, are a group of nonflowering plants that emerged several hundred million years before flowering plants angiosperms entered the evolutionary history of the plant kingdom. Skip to main content. Angiosperms vs Gymnosperms.
Posted by. Ryan Pankau. January 23, Mosses, hornworts, liverworts and some kinds of algae are modern day nonvascular plants and representatives of early plant life on land The development of a vascular system was a major step forward for the plant kingdom, occurring around million years ago.
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