The first three have been erected in the course of time out of Jeffrey's 2,3,5,5a original Lycopsida. The three divisions and these two subdivisions make five groups of plants widely recognized as distinct groups, though accorded a variety of taxonomic ranks.
Eames, A. Google Scholar. Jeffrey, E. Boston Soc. Article Google Scholar. Scott, D. London: A and C. Black, Ltd. Book Google Scholar. Bower, F. Rendle, A. Cambridge: The University Press, Just, Th. Dormer, K. Wardlaw, C. Ball, E. Newman, I. Photosynthesis takes place in their green stems; small yellow knobs form at the tip of the branch stem and contain the sporangia. Whisk ferns were considered an early pterophytes. However, recent comparative DNA analysis suggests that this group may have lost both leaves and roots through evolution and is more closely related to ferns.
With their large fronds, ferns are the most-readily recognizable seedless vascular plants. More than 20, species of ferns live in environments ranging from tropics to temperate forests. Although some species survive in dry environments, most ferns are restricted to moist, shaded places.
Ferns made their appearance in the fossil record during the Devonian period and expanded during the Carboniferous. The dominant stage of the life cycle of a fern is the sporophyte, which typically consists of large compound leaves called fronds. Fronds fulfill a double role; they are photosynthetic organs that also carry reproductive structure. The stem may be buried underground as a rhizome from which adventitious roots grow to absorb water and nutrients from the soil, or they may grow above ground as a trunk in tree ferns.
Adventitious organs are those that grow in unusual places, such as roots growing from the side of a stem. Most ferns produce the same type of spores and are, therefore, homosporous. The diploid sporophyte is the most conspicuous stage of the life cycle.
On the underside of its mature fronds, sori singular, sorus form as small clusters where sporangia develop. Sporangia in a sorus produce spores by meiosis and release them into the air. Those that land on a suitable substrate germinate and form a heart-shaped gametophyte, which is attached to the ground by thin filamentous rhizoids. The inconspicuous gametophyte harbors both sex gametangia.
Flagellated sperm are released and swim on a wet surface to where the egg is fertilized. The newly-formed zygote grows into a sporophyte that emerges from the gametophyte, growing by mitosis into the next generation sporophyte. Sori on a fern frond : Sori appear as small bumps on the underside of a fern frond.
Seedless vascular plants provide many benefits to life in ecosystems, including food and shelter and, to humans, fuel and medicine. Mosses and liverworts are often the first macroscopic organisms to colonize an area, both in a primary succession where bare land is settled for the first time by living organisms or in a secondary succession where soil remains intact after a catastrophic event wipes out many existing species.
Their spores are carried by the wind, birds, or insects. Once mosses and liverworts are established, they provide food and shelter for other species. In a hostile environment, such as the tundra where the soil is frozen, bryophytes grow well because they do not have roots and can dry and rehydrate rapidly once water is again available. Mosses are at the base of the food chain in the tundra biome. Many species, from small insects to musk oxen and reindeer, depend on mosses for food.
In turn, predators feed on the herbivores, which are the primary consumers. Some reports indicate that bryophytes make the soil more amenable to colonization by other plants. Because they establish symbiotic relationships with nitrogen-fixing cyanobacteria, mosses replenish the soil with nitrogen. At the end of the nineteenth century, scientists observed that lichens and mosses were becoming increasingly rare in urban and suburban areas.
Since bryophytes have neither a root system for absorption of water and nutrients, nor a cuticle layer that protects them from desiccation, pollutants in rainwater readily penetrate their tissues; they absorb moisture and nutrients through their entire exposed surfaces. Therefore, pollutants dissolved in rainwater penetrate plant tissues readily and have a larger impact on mosses than on other plants. The disappearance of mosses can be considered a bioindicator for the level of pollution in the environment.
Ferns contribute to the environment by promoting the weathering of rock, accelerating the formation of topsoil, and slowing down erosion by spreading rhizomes in the soil. The water ferns of the genus Azolla harbor nitrogen-fixing cyanobacteria and restore this important nutrient to aquatic habitats.
Seedless plants have historically played a role in human life through uses as tools, fuel, and medicine. Dried peat moss, Sphagnum , is commonly used as fuel in some parts of Europe and is considered a renewable resource. Sphagnum bogs are cultivated with cranberry and blueberry bushes. The ability of Sphagnum to hold moisture makes the moss a common soil conditioner.
Florists use blocks of Sphagnum to maintain moisture for floral arrangements. Plants as a renewable resource for fuel : Sphagnum acutifolium is dried peat moss and can be used as fuel.
The attractive fronds of ferns make them a favorite ornamental plant. Because they thrive in low light, they are well suited as house plants. More importantly, fiddleheads are a traditional spring food of Native Americans in the Pacific Northwest and are popular as a side dish in French cuisine.
The licorice fern, Polypodium glycyrrhiza , is part of the diet of the Pacific Northwest coastal tribes, owing in part to the sweetness of its rhizomes. It has a faint licorice taste and serves as a sweetener. The rhizome also figures in the pharmacopoeia of Native Americans for its medicinal properties and is used as a remedy for sore throat. Fiddlehead ferns as food : A chicken dish with fiddlehead ferns as a side is shown. Native Americans traditionally cook fiddleheads with meals during the spring.
By far the greatest impact of seedless vascular plants on human life, however, comes from their extinct progenitors. The tall club mosses, horsetails, and tree-like ferns that flourished in the swampy forests of the Carboniferous period gave rise to large deposits of coal throughout the world. Coal provided an abundant source of energy during the Industrial Revolution, which had tremendous consequences on human societies, including rapid technological progress and growth of large cities, as well as the degradation of the environment.
Coal is still a prime source of energy and also a major contributor to global warming. Carboniferous period plants : This drawing depicts the tall mosses and tree-like ferns of the Carboniferous period that deposited the large amounts of coal throughout the world.
Privacy Policy. Skip to main content. Seedless Plants. Search for:. Seedless Vascular Plants. Seedless Vascular Plants Seedless vascular plants, which reproduce and spread through spores, are plants that contain vascular tissue, but do not flower or seed. Learning Objectives Evaluate the evolution of seedless vascular plants. Key Takeaways Key Points The life cycle of seedless vascular plants alternates between a diploid sporophyte and a haploid gametophyte phase.
Seedless vascular plants reproduce through unicellular, haploid spores instead of seeds; the lightweight spores allow for easy dispersion in the wind. Seedless vascular plants require water for sperm motility during reproduction and, thus, are often found in moist environments.
Key Terms spermatophyte : any plant that bears seeds rather than spores embryophyte : any member of the subkingdom Embryophyta; most land plants bryophyte : seedless, nonvascular plants that are the closest extant relative of early terrestrial plants. The Major Divisions of Land Plants The green algae, known as the charophytes, and land plants are grouped together into a subphylum called the Streptophytina and are, therefore, called Streptophytes.
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