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Oct 31, 2023 · Characteristics of Gymnosperms. Gymnosperms are seed plants adapted to life on land; thus, they are autotrophic, photosynthetic organisms that tend to conserve water. They have a vascular system (used for the transportation of water and nutrients) that includes roots, xylem, and phloem.
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gymnosperm, any vascular plant that reproduces by means of an exposed seed, or ovule—unlike angiosperms, or flowering plants, whose seeds are enclosed by mature ovaries, or fruits. The seeds of many gymnosperms (literally, “naked seeds”) are borne in cones and are not visible until maturity. Taxonomists recognize four distinct divisions of extant (nonextinct) gymnospermous plants—Pinophyta, Cycadophyta, Ginkgophyta, and Gnetophyta—with 88 genera and more than 1,000 species distributed throughout the world.
Gymnosperms were dominant in the Mesozoic Era (about 252.2 million to 66 million years ago), during which time some of the modern families originated (Pinaceae, Araucariaceae, Cupressaceae). Although since the Cretaceous Period (about 145 million to 66 million years ago) gymnosperms have been gradually displaced by the more recently evolved angiosperms, they are still successful in many parts of the world and occupy large areas of Earth’s surface. Conifer forests, for example, cover vast regions of northern temperate lands, and gymnosperms frequently grow in more northerly latitudes than do angiosperms.
In all living gymnosperm groups, the visible part of the plant body (i.e., the growing stem and branches) represents the sporophyte, or asexual, generation, rather than the gametophyte, or sexual, generation. Typically, a sporophyte has a stem with roots and leaves and bears the reproductive structures. As vascular plants, gymnosperms contain two conducting tissues, the xylem and phloem. The xylem conducts water and minerals from the roots to the rest of the plant and also provides structural support. The phloem distributes the sugars, amino acids, and organic nutrients manufactured in the leaves to the nonphotosynthetic tissues of the plant.
In most gymnosperms the male pollen cones, called microstrobili, contain reduced leaves called microsporophylls. Microsporangia, or pollen sacs, are borne on the lower surfaces of the microsporophylls. The number of microsporangia may vary from two in many conifers to hundreds in some cycads. Within the microsporangia are cells which undergo meiotic division to produce haploid microspores.
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The gametophyte phase begins when the microspore, while still within the microsporangium, begins to germinate to form the male gametophyte. A single microspore nucleus divides by mitosis to produce a few cells. At this stage the male gametophyte (called a pollen grain) is shed and transported by wind or insects.
Female ovulate cones, called megastrobili, may be borne on the same plant that bears microstrobili (as in conifers) or on separate plants (as in cycads and Ginkgo). A megastrobilus contains many scales, called megasporophylls, that contain megasporangia. Within each megasporangium, a single cell undergoes meiotic division to produce four haploid megaspores, three of which typically degenerate. The remaining megaspore undergoes mitosis to form the female gametophyte. As the number of free nuclei multiplies, the megasporangium and megaspore wall expand. At this stage the ovule is ready to be fertilized.
Oct 26, 2024 · Characteristics: Diverse group with some species resembling angiosperms due to vessel elements in xylem. Examples : Welwitschia (Welwitschia mirabilis), Ephedra, Gnetum. There are several extinct gymnosperm orders, particularly from ancient periods when gymnosperms were much more diverse.
Apr 2, 2018 · Gymnosperms have needle-like or scale-like leaves and no flowers. The leaves have a waxy cuticle that reduces water loss and helps snow to slide off easily, reducing the weight load on the branches. Their wood is softer than that of angiosperms and is used to make paper and lumber.
Gymnosperms are a group of vascular plants which do not produce flowers but form seeds. Explore the characteristics, examples and classification of gymnosperms only at BYJU'S.
Aug 3, 2023 · Characteristics of Gymnosperms. The gymnosperm is a woody plant with seeds on the inner side of scale leaves that are usually arranged spirally to form cones or strobili but without flowers. Intermediated group between Cryptogams and Angiosperms. As gymnosperm lacks an ovary, it can’t produce fruit.
Oct 8, 2024 · Key Species: Coastal redwoods (Sequoia sempervirens), Monterey pine (Pinus radiata), and other conifers. Characteristics: Coastal habitats often have moderate temperatures and high humidity. Gymnosperms in these regions are adapted to salt spray and occasional flooding.
