Lycopodium is the largest genus in the family. The order Lycopodiales contains just one family, Lycopodiaceae, which has around 400 species. Lycopods were the first group of pteridophytes to evolve, making them the oldest vascular plants.Ĭlubmosses (sometimes written as two words, club moss) make up the most ancient group of lycopods and originated around 380 million years ago. The lycopods are the “allies” of ferns and fern allies and are sometimes referred to as lycophytes. The following list of groups is not exhaustive, as there are several smaller orders and families of Pteridophytes not discussed. Here, we follow the most recent and most widely accepted classification of pteridophytes made by the Pteridophyte Phylogeny Group. The classification of Pteridophytes has changed a lot in recent years thanks to genetic and molecular analyses. The group “Pteridophyta” was once used to encompass ferns and fern allies, but this group is no longer valid. Pteridophyte taxonomy has been in constant flux for quite some time. While not nearly as diverse as other groups of plants, like flowering plants, ferns and allies still exhibit a stunning array of forms and functions. There are approximately 12,000 species of pteridophytes. This new structure is diploid, and through mitosis, it develops into a new sporophyte. The fusion of a sperm and an egg results in a zygote. For this reason, it’s rare to find pteridophytes in extremely dry places like deserts. Sexual reproduction only occurs when water is present. Once it arrives, it fertilizes the egg contained within. In the presence of water, a sperm uses its flagella to swim towards an archegonium, attracted by chemical signals. The archegonium forms the eggs, while the antheridium produces sperm. They are formed in structures called archegonia or antheridia. These gametes are haploid (1n) and contain only half of the genetic information of the plant. Gametophytes produce gametes (eggs or sperm) through mitosis. It’s usually incapable of self-fertilizing, so it must reproduce with a nearby, genetically distinct individual. Unlike the sporophyte, a gametophyte reproduces sexually. The gametophyte, sometimes referred to as a prothallus, is multicellular, microscopic, and generally short-lived. The gametophytes that result from a heterosporous plant are thus dioecious, either female or male. Heterosporous plants produce two kinds of spores – megaspores and microspores – which are female and male, respectively. Conversely, a pteridophyte that produces two types of spores is called heterosporous. Homosporous plants produce only one type of spore that contains both male and female parts. The spores are then dispersed by wind or water to start the next generation, the gametophyte.Ī pteridophyte that produces one type of spore is called homosporous. Spores are released from a sporangium, usually in dry conditions when the outer casing cracks and opens up. Sporangia are structures in which spores are formed through meiosis. Such fertile fronds are called sporophylls. When a sporophyte is mature, it produces sporangia on the underside of fertile leaves or stems. Sporophytes are diploid (2n) and contain two pairs of each chromosome in a cell. Thus, all ferns that we see growing in the forest represent the sporophyte generation. The sporophyte is the only generation that is conspicuous. The main generation is the sporophyte, which is the dominant phase. This means that a plant must complete two distinct generations in order to complete its life cycle. Pteridophytes, like many other plants, exhibit true alternation of generations. Vascular bundles and vascular rings are akin to the vascular tissue organization of two angiosperm groups, monocots and dicots. Alternatively, some ferns possess vascular rings in the stem that surround the pith. That is, when looking at a cross-section of a stem, there are distinct bundles of xylem and phloem. Most Pteridophytes have bundled vascular tissue.
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