What do angiosperms have

The ferns and "fern allies" formed the great planetary forests of the late Paleozoic. 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. Angiosperms have male sex organs called stamens. On the end of the stamen is the anther. This is where pollen is made. The pollen has to be taken to the pistil or the female part of the flower.

The pollen is left on the stigma at the end of the pistil. The stigma carries the pollen down a tube called the style to the ovary. These angiosperms start with one seed-leaf. The main veins of their leaves are usually unbranched. There are about 30, species of monocots. Monocots include orchids, lilies, irises, palms, grasses, and grains like wheat, corn and oats.

The Laurales grow mostly in warmer climates and are small trees and shrubs. Familiar plants in this group include the bay laurel, cinnamon, spice bush Figure a , and avocado tree.

Plants in the monocot group are primarily identified by the presence of a single cotyledon in the seedling. Other anatomical features shared by monocots include veins that run parallel to and along the length of the leaves, and flower parts that are arranged in a three- or six-fold symmetry.

True woody tissue is rarely found in monocots. In palm trees, vascular and parenchyma tissues produced by the primary and secondary thickening meristems form the trunk. The pollen from the first angiosperms was likely monosulcate , containing a single furrow or pore through the outer layer. This feature is still seen in the modern monocots. Vascular tissue of the stem is scattered, not arranged in any particular pattern, but is organized in a ring in the roots.

The root system consists of multiple fibrous roots, with no major tap root. Adventitious roots often emerge from the stem or leaves. The monocots include familiar plants such as the true lilies Liliopsida , orchids, yucca, asparagus, grasses, and palms.

Many important crops are monocots, such as rice and other cereals, corn, sugar cane, and tropical fruits like bananas and pineapples Figure a , b , c. Eudicots, or true dicots , are characterized by the presence of two cotyledons in the developing shoot. Veins form a network in leaves, and flower parts come in four, five, or many whorls. Vascular tissue forms a ring in the stem; in monocots, vascular tissue is scattered in the stem.

Eudicots can be herbaceous not woody , or produce woody tissues. Most eudicots produce pollen that is trisulcate or triporate, with three furrows or pores. The root system is usually anchored by one main root developed from the embryonic radicle. Eudicots comprise two-thirds of all flowering plants. The major differences between monocots and eudicots are summarized in Figure.

However, some species may exhibit characteristics usually associated with the other group, so identification of a plant as a monocot or a eudicot is not always straightforward. Angiosperms are the dominant form of plant life in most terrestrial ecosystems, comprising about 90 percent of all plant species.

Most crops and ornamental plants are angiosperms. Their success comes from two innovative structures that protect reproduction from variability in the environment: the flower and the fruit.

Flowers were derived from modified leaves; their color and fragrance encourages species-specific pollination. The main parts of a flower are the sepals and petals, which protect the reproductive parts: the stamens and the carpels. The stamens produce the male gametes in pollen grains.

The carpels contain the female gametes the eggs inside the ovules , which are within the ovary of a carpel. The walls of the ovary thicken after fertilization, ripening into fruit that ensures dispersal by wind, water, or animals.

The angiosperm life cycle is dominated by the sporophyte stage. Double fertilization is an event unique to angiosperms. One sperm in the pollen fertilizes the egg, forming a diploid zygote, while the other combines with the two polar nuclei, forming a triploid cell that develops into a food storage tissue called the endosperm. Flowering plants are divided into two main groups, the monocots and eudicots, according to the number of cotyledons in the seedlings. Basal angiosperms belong to an older lineage than monocots and eudicots.

Figure If a flower lacked a megasporangium, what type of gamete would not form? Figure Without a megasporangium, an egg would not form; without a microsporangium, pollen would not form. Which of the following structures in a flower is not directly involved in reproduction? Corn develops from a seedling with a single cotyledon, displays parallel veins on its leaves, and produces monosulcate pollen.

It is most likely:. Some cycads are considered endangered species and their trade is severely restricted. Customs officials stop suspected smugglers who claim that the plants in their possession are palm trees, not cycads.

How would a botanist distinguish between the two types of plants? The resemblance between cycads and palm trees is only superficial. Cycads are gymnosperms and do not bear flowers or fruit. Cycads produce cones: large, female cones that produce naked seeds, and smaller male cones on separate plants.

Palms do not. What are the two structures that allow angiosperms to be the dominant form of plant life in most terrestrial ecosystems? Angiosperms are successful because of flowers and fruit. These structures protect reproduction from variability in the environment. Skip to content Seed Plants. Learning Objectives By the end of this section, you will be able to do the following: Explain why angiosperms are the dominant form of plant life in most terrestrial ecosystems Describe the main parts of a flower and their functions Detail the life cycle of a typical gymnosperm and angiosperm Discuss the similarities and differences between the two main groups of flowering plants.

These flowers grow in a botanical garden border in Bellevue, WA. Flowering plants dominate terrestrial landscapes. The vivid colors of flowers and enticing fragrance of flowers are adaptations to pollination by animals like insects, birds, and bats. Flowers Flowers are modified leaves, or sporophylls, organized around a central receptacle. Flower structure. This image depicts the structure of a perfect flower.

Perfect flowers produce both male and female floral organs. The flower shown has only one carpel, but some flowers have a cluster of carpels. Together, all the carpels make up the gynoecium. Visual Connection. Angiosperm life cycle.