It is possible that vessel elements arose independently in the two groups, Conifers are the dominant phylum of gymnosperms, with the greatest variety of species ((Figure)). (a) Ephedra viridis, known by the common name Mormon tea, grows on the West Coast of the United States and Mexico. Conifers share the following characteristics: The Pinaceae is currently the largest family of conifers, so many of our examples for this group of gymnosperms will be from the type genus Pinus (pines). External Features, Origin, and Internal Structure, Electron Transport Chain, Phosphorylation. The largest phylum, Coniferophyta, is represented by conifers, the predominant plants at high altitude and latitude. The megagametophyte is retained within the megasporangium, which becomes the nucellus. Some conifers are deciduous, such as larch (Larix), bald cypress (Taxodium), and the dawn redwood (Metasequoia). Pollination Water is no longer required for sperm to unite with egg; instead the partly developed male gametophyte (= pollen grain) is transferred to the vicinity of a female gametophyte within the ovule: this is known as pollination. The gametophytes (1n)microspores and megasporesare reduced in size. Coniferophyta, Cycadophyta, and Ginkgophyta are similar in their pattern of seed development and also in their production of secondary cambium (cells that generate the vascular system of the trunk or stem and are partially specialized for water transportation). Like angiosperms, they have broad leaves. Therefore, they are monoecious plants. Conifers are the dominant phylum of gymnosperms, with the most variety of species (Figure 2). Shown here are the (a) evergreen spruce Picea sp., (b) juniper Juniperus sp., (c) sequoia Sequoia Semervirens, which is a deciduous gymnosperm, and (d) the tamarack Larix larcinia. Cycads thrive in mild climates, and are often mistaken for palms because of the shape of their large, compound leaves. Other conifers. Ephedra occurs in dry areas of the West Coast of the United States and Mexico. Their characteristics include naked seeds, separate female and male gametes, pollination by wind, and tracheids (which transport water and solutes in the vascular system). It may take more than a year between pollination and fertilization while the pollen tube grows towards the growing female gametophyte (1n), which develops from a single megaspore. Regina Bailey Updated on May 02, 2018 Gymnosperms are flowerless plants that produce cones and seeds. Also known as gnetales, gnetophytes have a woody anatomy, similar to conifers and cycads, but differ from all three gymnosperms insomuch as they contain vessel element cell types, something that the other gymnosperms do not have. The term strobilus (plural = strobili) describes a tight arrangement of sporophylls around a central stalk, as seen in cones. Some conifers are deciduous, such as larch ( Larix), bald cypress ( Taxodium), and the dawn redwood ( Metasequoia). In the male cones, or staminate cones, the microsporocytes give rise to pollen grains by meiosis. Like all gymnosperms, pines are heterosporous and generate two different types of spores: male microspores and female megaspores. Water evaporation from leaves is reduced by their thin shape and the thick cuticle. (credit a: modification of work by USDA; credit b: modification of work by Malcolm Manners; credit c: modification of work by Derek Keats). The LibreTexts libraries arePowered by NICE CXone Expertand are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. Their characteristics include naked seeds, separate female and male gametes, pollination by wind, and tracheids (which transport water and solutes in the vascular system). Choose a different color to represent haploid and diploid tissues. Protecting the embryo In seed plants, the union of a female gamete with a male gamete produces a (n) zygote Firs, cedars, cypresses, spruces, and pines are all members of what phylum? They are adapted to live where fresh water is scarce during part of the year, or in the nitrogen-poor soil of a bog. The Process of Meiosis Sexual Reproduction Chromosomal Theory and Genetic Linkage Chromosomal Basis of Inherited Disorders Population Evolution Population Genetics Adaptive Evolution Chordates Fishes Amphibians Reptiles Birds Mammals The Evolution of Primates The Plant Body Stems Roots Leaves Transport of Water and Solutes in Plants Upon fertilization, the diploid egg will give rise to the embryo, which is enclosed in a seed coat of tissue from the parent plant. Megasporocytes will eventually produce which of the following? Gnetophytes are the closest relative to modern angiosperms, and include three dissimilar genera of plants: Ephedra, Gnetum, andWelwitschia (Figure 5). gnetophyte, (division Gnetophyta), any member of the division Gnetophyta, a small group of gymnospermous vascular plants that are represented by three living genera: Ephedra, Gnetum, and Welwitschia. gametophytes The purpose of resin in pines is to - protect against insects and fungi Select a feature that distinguishes gymnosperms from angiosperms. All gymnosperms are heterosporous. Explain your reasoning. Adaptations to cold and dry weather explain the predominance of conifers at high altitudes and in cold climates. Evergreen conifers continue low levels of photosynthesis during the cold months, and are ready to take advantage of the first sunny days of spring. Not all of the conifers resemble the needleleaved pines in appearance or length of time to complete the sexual reproductive cyclemost take only a year. The sporophyte (2n) phase is the longest phase in the life of a gymnosperm. Observe the gnetophyte specimens available in lab. The life cycle of a pine is a slow, twoyear process (Figure ). (Figure) At what stage does the diploid zygote form? Ginkgo. The four phyla of living gymnosperms are of separate clades or lineages, unlike the angiosperms, which are a monophyletic, single lineage. The species of Ephedra have green, jointed stems and small scalelike leaves. The eggs in the megagametophyte move towards the pollen tubes in their own tubelike structures; fertilization takes place after the two tubes fuse. First, she told us about animals and plants. Though currently low in diversity, these amazing plants make up 30% of Earths forests. Male and female sporangia are produced either on the same plant, described as monoecious (one home or bisexual), or on separate plants, referred to as dioecious (two homes or unisexual) plants. Pollen from male cones blows up into upper branches, where it fertilizes female cones. In the spring, large amounts of yellow pollen are released and carried by the wind. We also use third-party cookies that help us analyze and understand how you use this website. In the male cones, or staminate cones, the microsporocytes give rise to pollen grains by meiosis. The megagametophyte is part of the ovule and contains (usually) two archegonia, each with an egg cell inside. In the spring of the year following pollination, events come together: The eggs in the two to three archegonia are fertilized (polyembryony), and development of the new sporophytic generation begins. Then again, she told us that land plants belong to two broad categories vascular plants and non-vascular plants (bryophyes). Primarily evergreen, but some species are deciduous (e.g. However, the three phyla are not closely related phylogenetically to each other. bookmarked pages associated with this title. Label the mesophyll, guard cells, stoma, hypodermis, epidermis, and cuticle. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, Ginkgo, and gnetophytes, forming the clade Gymnospermae. They are adapted to live where fresh water is scarce during part of the year, or in the nitrogen-poor soil of a bog. The term strobilus (plural = strobili) describes a tight arrangement of sporophylls around a central stalk, as seen in cones. and any corresponding bookmarks? Reproductive structures are located in a flower. The cycads look like palms with cones and are prevalent worldwide in the tropics and subtropics (two species grow wild in Florida). Ephedras small, scale-like leaves are the source of the compound ephedrine, which is used in medicine as a potent decongestant. Thus, a tree remains evergreen. It is planted in public spaces because it is unusually resistant to pollution. It may take more than year between pollination and fertilization while the pollen tube grows towards the megasporocyte (2n), which undergoes meiosis into megaspores. Three living generanone of whom resemble one another or any other living gymnospermconstitute the Gnetophyta, Gnetum, Ephedra, and Welwitschia. Because of their attractive shape, they are often used as ornamental plants in gardens in the tropics and subtropics. Read the following article for a simple yet explanatory overview of the various types of gymnosperm plants. Cycads (phylum Cycadophyta) resemble palm trees and grow in tropical climates. They appeared in the Paleozoic period and were the dominant plant life during the Mesozoic. Seventeen species of conifers are growing in small numbers along the California coastand nowhere else. The seed that is formed contains three generations of tissues: the seed coat that originates from the sporophyte tissue, the gametophyte tissue that will provide nutrients, and the embryo itself. Ginkgo trees are either male or female, so they are said to be . The life cycle of a gymnosperm involves alternation of generations, with a dominant sporophyte in which the female gametophyte resides, and reduced gametophytes. The European larch and the tamarack are examples of deciduous conifers (Figure 2c). The sporophyte (2n) phase is the longest phase in the life of a gymnosperm. (credit a: modification of work by USDA; credit b: modification of work by Malcolm Manners; credit c: modification of work by Derek Keats). Like angiosperms, but unlike other gymnosperms, all gnetophytes possess vessel elements in their xylem. Leaves xerophytic with opposite arrangement, Primarily insect pollinated; brightly colored seeds are dispersed by birds. Snow easily slides off needle-shaped leaves, keeping the snow load light, thus reducing broken branches. This seeming lack of syncronization is of little concern because it takes the pollen tube over a year to digest its way through nucellular tissues to the archegoniawhich gives ample time for megagametophyte preparationsand for the immature male gametophyte (the fourcelled germinated pollen grain) to produce two sperm cells by division of the generative cell. Water evaporation from leaves is reduced by their narrow shape and a thick cuticle. By the end of this section, you will be able to do the following: Gymnosperms, meaning naked seeds, are a diverse group of seed plants. "Gymnosperm" means "naked seed" and the name draws attention to the ovules and resulting seeds that are exposed openly on the megasporophylls. Modern-day gymnosperms belong to four phyla. At what stage does the diploid zygote form? However, the true nature of this evolutionary relationship remains murky and contentious. Coniferophyta, Cycadophyta, and Ginkgophyta are similar in their production of secondary cambium (cells that generate the vascular system of the trunk or stem and are partially specialized for water transportation) and their pattern of seed development. Like angiosperms, but unlike other gymnosperms, all gnetophytes possess vessel elements in their xylem. Cycads (phylum Cycadophyta) resemble palm trees and grow in tropical climates. Indicate where fertilization and meiosis occur. The reproductive organs and paraphernalia, both male and female, of gymnosperms, are not contained within floral structures, and are usually exposed. The conifers are woody, mostly evergreen trees, with needleshaped or flattened leaves, which occupy the drier and cooler sites in the world today just as their ancestors probably did in the Permian. Conifers are the dominant form of vegetation in cold or arid environments and at high altitudes. Conifers. The gametophyte is the longest phase of the life cycle. The bark and wood of a typical ginkgo tree is usually very soft, and has a texture very similar to cork. The ovulate cones are large (some weigh over 30 kilograms) and are borne upright on megasporophylls among the vegetative leaves. Like the ginkgos, Welwitschia produces male and female gametes on separate plants. Therefore, they are monoecious plants. Like all gymnosperms, pines are heterosporous and generate two different types of spores: male microspores and female megaspores.
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