Overview
Vascular plants (also known as tracheophytes or higher plants) are those that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the ferns, clubmosses, flowering plants, conifers and other gymnosperms. Scientific names for the group include Tracheophyta1] and Tracheobionta,[2] but neither name is very widely used.
Characteristics
Vascular plants are distinguished by two primary characteristics:
- Vascular plants have vascular tissues, which circulate resources through the plant. This feature allows vascular plants to evolve to a larger size than non-vascular plants, which lack these specialized conducting tissues and are therefore restricted to relatively small sizes.
- In vascular plants, the principal generation phase is the sporophyte, which is usually diploid with two sets of chromosomes per cell. By contrast, the principal generation phase in non-vascular plants is usually the gametophyte, which is haploid with one set of chromosomes per cell.
Water transport happens in either xylem or phloem: xylem carries water and inorganic solutes upward toward the leaves from the roots, while phloem carries organic solutes throughout the plant. Group of plants having lignified conducting tissue (xylem vessels or tracheids).
Phylogeny
A proposed phylogeny of the vascular plants after Kenrick and Crane[3] is as follows, with modification to the Pteridophyta from Smith et al.[4]
Nutrient Distribution
Nutrients and water from the soil and the organic compound produces in leaves are distributed to specific areas in the plant through the xylem and phloem. The xylem draws water and nutrients up from the roots to the upper sections of the plant's body, and the phloem conducts other materials, such as the glucose produced during photosynthesis, which gives the plant energy to keep growing and seeding.
The xylem consists of tracheids, which are dead hard-walled cells arranged to form tiny tubes to function in water transport. A tracheid cell wall usually contains the polymer lignin. The phloem however consists of living cells called sieve-tube members. Between the sieve-tube members are sieve plates, which have pores to allow molecules to pass through. Sieve-tube members lack such organs as nuclei or ribosomes, but cells next to them, the companion cells, function to keep the sieve-tube members alive.
Movement of nutrients, water, sugars and waste is effected by transpiration, conduction and absorption.
Transpiration
The most abundant compound in most plants is water, serving a large role in the various processes taking place. Transpiration is the main process a plant can call upon to move compounds within its tissues. The basic minerals and nutrients a plant is composed of remain, generally, within the plant. Water, however, is constantly being lost from the plant through its metabolic and photosynthetic processes to the atmosphere.
Water is transpired from the plants leaves via stomata, carried there via leaf veins and vascular bundles within the plants cambium layer. The movement of water out of the leaf stomata creates, when the leaves are considered collectively, a transpiration pull. The pull is created through water surface tension within the plant cells. The draw of water upwards is assisted by the movement of water into the roots via osmosis. This process also assists the plant in absorbing nutrients from the soil as soluble salts, a process known as absorption.
Absorption
Xylem cells move water and nutrient solutions upwards towards other plant organs from the roots and fine root hairs. Living roots cells actively absorb water in the absence of transpiration pull via osmosis creating root pressure. There are times when plants do not have transpiration pull, usually due to lack of light or other environmental elements. Water in the plant tissues may move to the roots to assist in passive absorption.
Conduction
Xylem and phloem tissues are involved in the conduction processes within plants. The movement of foods throughout the plant takes place mainly in the phloem. Plant conduction (food movement) is from an area of high food content, place of manufacture (photosynthesis) or storage, to a place of food utilisation, or from a point of manufacture to storage tissues. Mineral salts are translocated in the xylem tissues.[5]
Photos
Taxonomy
The Phylum Tracheophyta is further organized into finer groupings including:
- Subphylum (5): Euphyllophytina · Lycophytina · Pteridophytina · Rhyniophytina · Trimerophytina
- Infraphylum (5): Filices · Lycophytae · Moniliformopses · Psilophytae · Radiatopses
- Class (17): Cycadopsida · Equisetopsida · Filicopsida · Ginkgoopsida · Gnetopsida · Lagenostomopsida · Liliopsida · Lycopsida · Magnoliopsida · Marattiopsida · Pinopsida · Polypodiopsida · Psilotopsida · Pteridospermopsida · Rhyniopsida · Trimerophytopsida · Zosterophyllopsida
- Species: ZipcodeZoo has pages for 744,704 species, subspecies, varieties, forms, and cultivars in the Phylum Tracheophyta.
Classes
Cycadopsida
Cycads are a group of characterized by a large crown of compound leaves and a stout trunk. They are evergreen, gymnospermous, dioecious plants having large pinnately compound leaves. They are frequently confused with and mistaken for palms or ferns, but are related to neither, belonging to the division Cycadophyta. [more]
Equisetopsida
Equisetopsida, or Sphenopsida, is a of plants with a fossil record going back to the Devonian. Living species are commonly known as horsetails and typically grow in wet areas, with needle-like leaves radiating at regular intervals from a single vertical stem. Equisetopsida is placed in the botanical division of ferns (Pteridophyta), though sometimes regarded as a separate division Equisetophyta (also as Sphenophyta or Arthrophyta). [more]
Filicopsida
Ginkgoopsida
The Ginkgoaceae is a family of which appeared during the Mesozoic Era, of which the only extant representative is Ginkgo biloba, which is for this reason sometimes regarded as a living fossil. Formerly, however, there were several other genera. [more]
Gnetopsida
The division Gnetophyta or gnetophytes comprise three related families of woody plants grouped in the gymnosperms. The gnetophytes differ from other gymnosperms in having vessel elements as in the flowering plants (Angiosperms or Magnoliophytes). [more]
Lagenostomopsida
Liliopsida
Lycopsida
Lycopodiopsida is a class of plants often loosely grouped as the , and includes the clubmosses. Lycopodiopsida traditionally included all the clubmosses, including Selaginella and Isoetes. However, subdivisions within the Division Lycopodiophyta are now considered ancient enough to warrant higher-level separation in accordance with cladistics. [more]
Magnoliopsida
Marattiopsida
Pinopsida
The conifers, division Pinophyta, also known as division Coniferae, are one of 13 or 14 level taxa within the Kingdom Plantae. They are cone-bearing seed plants with vascular tissue; all extant conifers are woody plants, the great majority being trees with just a few being shrubs. Typical examples of conifers include cedars, douglas-firs, cypresses, firs, junipers, kauris, larches, pines, redwoods, spruces, and yews. Species of conifers can be found growing naturally in almost all parts of the world, and are frequently dominant plants in their habitats, as in the taiga, for example. Conifers are of immense economic value, primarily for timber and paper production; the wood of conifers is known as softwood. The division contains approximately 630 living species. [more]
Polypodiopsida
The Pteridopsida is a class of in the Division Pteridophyta that includes all the leptosporangiate ferns. In the recent 2006 classification by Smith et al. the class is renamed Polypodiopsida. This recent reclassification of Monilophyte (ferns) is based on multiple molecular studies published since 1994 that have clarified some of the confusion of the placement and relations among fern families. Polypodiopsida is one of four classes of Monilophytes (an Infradivision, this rank is not recognized by the International Code of Botanical Nomenclature), the other three being Marattiopsida, Equisetopsida, and Psilotopsida.
[more]
Psilotopsida
Psilotopsida is a class of -like plants. As circumscribed by Smith et al. (2006) it contains two families, Psilotaceae and Ophioglossaceae, placed in orders Psilotales and Ophioglossales, respectively. The affinities of these two groups have long been unclear and a close relationship between them has only recently been confirmed through molecular systematic studies. Psilotopsida is the sister-group to all other ferns (including Marattiaceae and Equisetaceae). [more]
Pteridospermopsida
Rhyniopsida
Trimerophytopsida
Zosterophyllopsida
At least 295 species and subspecies belong to the Class Zosterophyllopsida.
More info about the Class Zosterophyllopsida may be found here.
References
- ^ Abercrombie, Hickman & Johnson. 1966. A Dictionary of Biology. (Penguin Books
- ^ ITIS Standard Report Page: Tracheobionta
- ^ Kenrick, Paul & Peter R. Crane. 1997. The Origin and Early Diversification of Land Plants: A Cladistic Study. (Washington, D.C.: Smithsonian Institution Press). ISBN 1-56098-730-8.
- ^ Smith, Alan R., Kathleen M. Pryer, E. Schuettpelz, P. Korall, H. Schneider, & Paul G. Wolf. (2006). "A classification for extant ferns". Taxon 55(3): 705-731.
- ^ Robbins, W.W., Weier, T.E., et al, Botany:Plant Science, 3rd edition , Wiley International, New York, 1965.
Sources
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