Which is older gymnosperms or angiosperms in the evolutionary scale

Note the difference between the broad leaves of the angiosperms on display, and compare them to the needle-shaped leaves of pines. Needles are an adaptation to conserve water in cold, dry environments.

They are also an excellent shape for species like pines that rely on wind pollination why? Examine slides of the megaspore mother cell. Observe the structure of the strobilus female pine cone and note the megasporophylls and megasporangia.

You will need to look at several sporangia , and possibly more than one slide, to actually find the megaspore mother cell. Notice that the sporangia sitting on the sporophylls are directly exposed to the outside air. Gymnosperm means "naked seed". Examine slides of the male strobilus pine cone. Note the microsporangia and the microsporophylls. You can switch to high power and observe the pollen grains in the sporangia or switch to the pollen grain slide.

Notice the two large wings looks like Mickey Mouse. These wings were presumed to aid in wind pollination, but recent evidence suggests they help the pollen grain float up through the micropyle to the egg. Examine the pine cones on display. The smaller male cones are only on the tree for a short time. Ephedra is the natural source of the drug ephedrin , which is used to treat hay fever, sinus headaches, and asthma eg.

Zamia floridana is the only cycad native to the U. Ginkgos are used for bonsai, as a source of herbal medicine, and as popular urban shade trees because of their yellow autumn foliage and their resistance to air pollution. Conifer seeds are very complex structures, containing cells from three generations of the tree.

Can you figure out which tissues come from which generation of the conifer? Just as Gymnosperms forced non-seed plants into the ecological background, the evolution of Angiosperms, sometime during the Cretaceous, forced gymnosperms into restricted habitats. Wherever the earth was cold or dry, gymnosperms could prevail.

But in all other habitats, flowering plants rapidly became the dominant plant life. Flowering plants are able to survive in a greater variety of habitats than gymnosperms. Flowering plants mature more quickly than gymnosperms, and produce greater numbers of seeds. The woody tissues of angiosperms are also more complex and specialized.

Their seeds are enclosed in a fruit for easy dispersal by wind, water, or animals. The leaves of angiosperms are mostly thin, extended blades, with an amazing diversity of shapes, sizes, and types. The surface of the pollen grain has a complex three-dimensional structure.

This structure is unique for each species, like a floral thumbprint. It also means that pollen grains, which are abundant in the fossil record, allow us to reconstruct ancient plant communities, and these communities in turn tells us about ancient climates. All angiosperms produce flowers , reproductive structures that are formed from four whorls of modified leaves. Most flowers have showy petals to attract pollinators, bribing insects and other animals with nectar, to get them to carry the male gametophyte through the air to another flower.

Animal pollination is common in angiosperms, in contrast to the mostly wind-pollinated gymnosperms. The ovules in angiosperms are encased in an ovary, not exposed on the sporophylls of a strobilus, as they are in gymnosperms. Angiosperm means "covered seed".

The ovules develop into seeds , and the wall of the ovary forms a fruit to contain those seeds. Fruits attract animals to disperse the seeds. Flowers consist of four whorls of modified leaves on a shortened stem: sepals , petals , stamens an anther atop a slender filament , and one or more carpels.

Imagine a broad leaf with sporangia fastened along the edges of the leaf. Some ferns actually look like this. Now fold that leave over along the midrib, and you've enclosed the sporangia in a protected chamber. You've just made a carpel. The carpels are fused together to form a pistil , which consists of a stigma upper surface , a style long, slender neck , and an ovary round inner chamber at the bottom containing one or more ovules.

The flower is analogous to the strobilus of pines and more primitive plants, except that only the inner two whorls stamens and carpels actually bear sporangia. The base of the flower is called the receptacle , and the tiny stalk that holds it is the pedicel. The life cycle of flowering plants is described in more detail below. Microspores develop in microsporangia in the anthers , at the tip of the stamen.

Each anther has four microsporangia. Microspores develops by meiosis from the microspore mother cell. These microspores develop into pollen grains.

Pollen grains are the male gametophytes in flowering plants. Inside the pollen grain, the microspore divides to form two cells, a tube cell and a cell that will act as the sperm. Cross walls break down between each pair of microsporangia, forming two large pollen sacs. These gradually dry out and split open to release the pollen. Meanwhile, inside the ovary, at the base of the carpel, the ovules, are developing, attached to the wall of the ovary by a short stalk.

The megasporangia is covered by an integument , protective tissues that are actually part of the parent sporophyte. The megaspore mother cell divides by meiosis to produce four haploid megaspores.

Three of these megaspores degenerate, and the surviving fourth megaspore divides by mitosis. Each of the daughter nuclei divides again, making four nuclei, and these divide a third time, making a grand total of eight haploid nuclei. This large cell with eight nuclei is the embryo sac. This embryo sac is the female gametophyte in flowering plants. One nucleus from each group of four migrates to the center.

These are called the polar nuclei. The remaining three nuclei of each group migrates to opposite ends of the cell. Cell walls form around each group of three nuclei. The mature female gametophyte thus consists of only seven cells, three at the top, three at the bottom, and a large cell in the middle with two nuclei. One cell of the bottom three cells will act as the egg. When the pollen grain reaches the stigma of the carpel, it germinates to form a pollen tube.

This pollen tube will grow through the neck or style, all the way down to the bottom of the carpel, to a small opening called the micropyle. The male gametophyte has two cells. One is the tube cell, the other will act as a sperm. As the pollen tube grows closer to the embryo sac, the sperm nucleus divides in two, so the mature male gametophyte has three haploid nuclei.

While the pollen tube is entering the ovule, the two polar nuclei in the female gametophyte fuse together, making one diploid nucleus. The two sperm nuclei enter the embryo sac. One sperm nucleus fuses with the egg nucleus to form a diploid zygote. The other sperm nucleus fuses with the fused polar nuclei to make a triploid cell.

This 3N cell will divide repeatedly to form the endosperm, the stored nutritive material inside the seed. The integuments develop into the tough outer seed coat, which will protect the developing embryo from mechanical harm or dessication. Thus the ovule, the integuments and the megasporangium they enclose, develops into the seed. The walls of the ovary then develop into the fruit.

There is an incredible diversity of flower structure, not only in the number of sepals, petals, stamens, and carpels, but also in the way these modified leaves are attached with respect to the ovary.

Linnaeus used these very characteristics to sort out the different related groups of flowering plants in his invention of binomial nomenclature, genus and species. All of these differences can affect the final physical appearance of the fruit.

The ovary wall has three layers, each of which can develop into a different part of the fruit. Simple fruits are fruits that develop from a single ovary.

They can be either dry , like grains, nuts and legumes, or fleshy , like apples, tomatoes and cucumbers. Compound fruits develop from a group of ovaries. They can be either multiple fruits or aggregate fruits. In multiple fruits , like the pineapple, the group of ovaries come from separate flowers. Each flower makes a fruit, and these fruit fuse together. In aggregate fruits , like strawberries and blackberries, the fruit develops from a flower with many carpels.

Each of these carpels develops as a separate fruitlet, that fuse together to form the compound fruit. Seeds all bear the plant version of the belly button. They have a crescent-shaped scar called a hilum , where the ovule was attached to the wall of the ovary. Right above the hilum, if you look very carefully, you can also see a little pinprick scar that is a vestige of the micropyle.

Inside the seed, the tiny sporophyte embryo develops. Somewhere around million years ago, the gymnosperms began to dominate the landscape on earth. Their conquest was fueled by the development of both seeds and pollen, which were major innovations in plant reproduction. Pollen grains could travel great distances to spread plant genes and seeds provided a protective coat around embryos. Seeds also built in a higher resistance to drought, allowing germination when conditions were optimal.

These factors pushed gymnosperms to expand into much drier terrestrial environments. Around million years ago, the angiosperms emerged in the fossil record. They are most commonly known for the development of a more specialized seed that forms inside the ovary of a flower, surrounded by a protective fruit.

With the development of flowers, the angiosperms began to incorporate and attract other life in their reproductive process. Pollinating insects became major players in the evolutionary history of angiosperms assisting them in and explosion of diversity around million years ago. Today, angiosperms dominate the plant world with an estimated ,, species, compared to a mere 1, species of gymnosperms.

The angiosperms include all the fruits and vegetables we eat, all of our native, deciduous trees and shrubs, as well as so many other plants that we encounter on a daily basis. A large number of pollinating insects also appeared during this same time. Although several hypotheses have been offered to explain this sudden profusion and variety of flowering plants, none have garnered the consensus of paleobotanists scientists who study ancient plants.

New data in comparative genomics and paleobotany have, however, shed some light on the evolution of angiosperms. Rather than being derived from gymnosperms, angiosperms form a sister clade a species and its descendents that developed in parallel with the gymnosperms.

The two innovative structures of flowers and fruit represent an improved reproductive strategy that served to protect the embryo, while increasing genetic variability and range. Paleobotanists debate whether angiosperms evolved from small woody bushes, or were basal angiosperms related to tropical grasses.

Both views draw support from cladistic studies. The so-called woody magnoliid hypothesis which proposes that the early ancestors of angiosperms were shrubs also offers molecular biological evidence. The most primitive living angiosperm is considered to be Amborella trichopoda , a small plant native to the rainforest of New Caledonia, an island in the South Pacific. Analysis of the genome of A.

A few other angiosperm groups, known as basal angiosperms, are viewed as primitive because they branched off early from the phylogenetic tree. Most modern angiosperms are classified as either monocots or eudicots based on the structure of their leaves and embryos. Basal angiosperms, such as water lilies, are considered more primitive because they share morphological traits with both monocots and eudicots.

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.