Ferns - General Characteristics, Natural History, Life Cycle, Gametophyte, Sporophyte, Polyploidy, Evolution, Modern Ferns
plants leaves phylum system
Ferns are plants in the Filicinophyta phylum, also called the Pteridophyta phylum. They are intermediate in complexity between the more primitive (i.e., evolutionarily ancient) bryophytes (mosses, liverworts, and hornworts) and the more advanced (or recent) seed plants. Like bryophytes, ferns reproduce sexually by making spores rather than seeds. Most ferns produce spores on the underside or margin of their leaves. Like seed plants, ferns have stems with a vascular system for efficient transport of water and food. Ferns also have leaves, known technically as megaphylls, with a complex system of branched veins. There are about 11,000 species of ferns, most of them indigenous to tropical and subtropical regions.
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A fern plant generally consists of one or more fronds attached to a rhizome. A frond is simply the leaf of the fern. A rhizome is a specialized, root-like stem. In most temperate-zone species of ferns, the rhizome is subterranean and has true roots attached to it. Fronds are generally connected to the rhizome by a stalk, known technically as the stipe. The structures of the frond, rhizome, and sti…
There are about 11,000 species of ferns in the world. Ferns are found throughout the world, from the tropics to the subarctic region. The greatest species diversity is in the tropical and subtropical region from southern Mexico to northern South America. In temperate North America, most ferns are terrestrial plants and grow in woodlands. However, in the tropics, many ferns grow as epiphytes. Epiph…
The gametophyte phase of the fern life cycle begins with a spore. A fern spore is a haploid reproductive cell, which unlike the seeds of higher plants, does not contain an embryo. Fern spores are often dispersed by the wind. Upon germination, a spore gives rise to a green, thread-like tissue, called a protonema. The protonema develops into a prothallus, a small, green, multicellular tissue that is…
Fusion of the egg and sperm nuclei during fertilization leads to the formation of a zygote, with the unreduced number of chromosomes, usually two sets. The zygote develops into a sporophyte, the most familiar stage of the fern life cycle. As the sporophyte grows, the prothallus to which it is attached eventually decays. Most fern sporophytes in temperate North America are green and terrestrial. As…
In many species of ferns, the sporophyte phase is diploid (two sets of chromosomes) and the gametophyte phase is haploid (one set of chromosomes). However, many other ferns are considered polyploid, in that their sporophyte contains three or more sets of chromosomes. In polyploid ferns, the gametophyte and sporophyte phases are said to have the "reduced" and the "unreduced�…
Most botanists believe that the ferns and fern allies are descendants of the Rhyniopsida, an extinct group of free-sporing plants which originated in the Silurian period (about 430 million years ago) and went extinct in the mid-Devonian period (about 370 million years ago). The Rhyniopsida were primitive vascular plants which were photosynthetic, had branched stems, and produced sporangia at their…
There are two evolutionarily distinct groups of modern ferns, the leptosporangiates and the eusporangiates. In the leptosporangiates, the sporangium develops from one cell and is usually only one cell thick. In the eusporangiates, the sporangium develops from several cells and is usually several cells thick. Most botanists believe that the leptosporangiate and eusporangiate ferns separated evoluti…
In general, ferns are of minor economic importance to humans. However, ferns are popular horticultural plants and many species are grown in ornamental gardens or indoors. Most people can recognize ferns as understory or groundcover plants in woodland habitats. However, several hundred million years ago ferns and fern allies were the dominant terrestrial plants. Thus, the fossils of these plants ha…
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