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''Calamites'' is a genus of extinct arborescent (tree-like) horsetails to which the modern horsetails (genus '' Equisetum'') are closely related. Unlike their
herbaceous Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition o ...
modern cousins, these plants were medium-sized trees, growing to heights of 30-50 meters (100-160 feet). They were components of the understories of
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dead ...
swamps of the
Carboniferous Period The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonif ...
(around ).


Taxonomy

A number of organ taxa have been identified as part of a united organism, which has inherited the name ''Calamites'' in popular culture. ''Calamites'' correctly refers only to casts of the stem of Carboniferous/Permian
sphenophyte Equisetidae is one of the four subclasses of Polypodiopsida (ferns), a group of vascular plants with a fossil record going back to the Devonian. They are commonly known as horsetails. They typically grow in wet areas, with whorls of needle-like ...
s, and as such is a form genus of little taxonomic value. There are two forms of casts, which can give mistaken impressions of the organisms. The most common is an internal cast of the hollow (or pith-filled) void in the centre of the trunk. This can cause some confusion: firstly, it must be remembered that a fossil was probably surrounded with 4-5 times its width in (unpreserved) vascular tissue, so the organisms were much wider than the internal casts preserved. Further, the fossil gets narrower as it attaches to a rhizoid, a place where one would expect there to be the highest concentration of vascular tissue (as this is where the peak transport occurs). However, because the fossil is a cast, the narrowing in fact represents a constriction of the ''cavity'', into which vascular tubes encroach as they widen. Further organ genera belonging to sphenophytes include: * ''
Arthropitys ''Arthropitys'' is an extinct genus of calamitacean equisetale. The petrified fossils of ''Arthropitys bistriata'', the type species, can be found at Chemnitz petrified forest, Chemnitz, Germany. History Petrified trunks of tree ferns, seed ...
'' (stems which are preserved in a mineralised form) * '' Astromyelon'' (permineralised rhizomes, distinguished from ''Arthropitys'' by the absence of a carinal canal) * ''
Annularia ''Annularia'' is a form taxon, applied to fossil foliage belonging to extinct plants of the genus ''Calamites'' in the order Equisetales. Description ''Annularia'' is a form taxon name given to leaves of ''Calamites''. In that species, the leav ...
'' and '' Asterophylites'' (
form genera Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships. Form classification, generally restricted to palaeontology, reflects uncertainty; the goal of sc ...
of leaf-whorls which are paraphyletic).


Anatomy

The trunks of ''Calamites'' had a distinctive segmented,
bamboo Bamboos are a diverse group of evergreen perennial flowering plants making up the subfamily Bambusoideae of the grass family Poaceae. Giant bamboos are the largest members of the grass family. The origin of the word "bamboo" is uncertain, but ...
-like appearance and vertical ribbing. The branches, leaves and cones were all borne in whorls. The leaves were needle-shaped, with up to 25 per whorl. Their trunks produced secondary
xylem Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from ...
, meaning they were made of wood. The
vascular cambium The vascular cambium is the main growth tissue in the stems and roots of many plants, specifically in dicots such as buttercups and oak trees, gymnosperms such as pine trees, as well as in certain other vascular plants. It produces secondary xyl ...
of ''Calamites'' was ''unifacial'', producing secondary xylem towards the stem center, but not secondary phloem. The stems of modern horsetails are typically hollow or contain numerous elongated air-filled sacs. ''Calamites'' was similar in that its trunk and stems were hollow, like wooden tubes. When these trunks buckled and broke, they could fill with sediment. This is the reason pith casts of the inside of ''Calamites'' stems are so common as fossils. Calamitaceae - Annularia stellata.JPG, Specimen of ''Annularia stellata'' from Italy on display at the
Museo Civico di Storia Naturale di Milano The Museo Civico di Storia Naturale di Milano (Milan Natural History Museum) is a museum in Milan, Italy. It was founded in 1838 when naturalist Giuseppe de Cristoforis donated his collections to the city. Its first director was Giorgio Jan. ...
Calamites reconstrucción.png, Reconstruction of a whole Calamites tree with
Annularia ''Annularia'' is a form taxon, applied to fossil foliage belonging to extinct plants of the genus ''Calamites'' in the order Equisetales. Description ''Annularia'' is a form taxon name given to leaves of ''Calamites''. In that species, the leav ...
.


Reproduction

''Calamites'' reproduced by means of spores, which were produced in small sacs organized into cones. They are also known to have possessed massive underground rhizomes, which allowed for the production of clones of one tree. This is the only group of trees of their period known to have a clonal habit. This type of
asexual reproduction Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the f ...
would allow them to spread quickly into new territory, and help to anchor them firmly in the unstable ground along rivers and in newly deposited delta sediments. The rhizomes of ''Calamites'' look quite similar to the stems in most cases, but have nodes that get progressively closer together as they approach the apical area (the growth tip that spreads outward through the soil).


Different forms

''Calamites'' come in a variety of different "form genera". One type, ''Calamites suckowi'', is distinguishable from other ''Calamites'' forms by its prominent, swollen nodes and relatively wide-spaced longitudinal ribs. Another example, ''Calamites cisti'', has much smaller nodes and the ribs are typically closer together. In addition, the distance between successive node lines on a ''Calamites suckowi'' specimen is typically much wider than the diameter. In other forms like ''Calamites cisti'', the opposite is true or the specimen is just slightly wider than the diameter. However, the value of these form taxa is limited. The distance between nodes, for example, is highly variable, and an intercalary meristem means that this distance varied as the organisms grew.


Extinction and classification

The genus ''Calamites'' is placed in the family
Calamitaceae Calamitaceae is an extinct family of plants related to the modern horsetails. Some members of this family attained tree-like stature during the Carboniferous Period (around ) and in Permian Period, reaching heights of up to 20 meters. The famil ...
in the plant class Equisetopsida (formerly known as Sphenophyta) in the fern allies division Pteridophyta. The Calamitaceae finally became extinct in the Lower Permian, a time which also saw the origin and diversification of the herbaceous genus '' Equisetum'', the only living sphenophyte genus.


See also

* ''
Archaeopteris ''Archaeopteris'' is an extinct genus of progymnosperm tree with fern-like leaves. A useful index fossil, this tree is found in strata dating from the Upper Devonian to Lower Carboniferous (), the oldest fossils being 385 million years old, and ...
''


References


How large are the giant horsetails?
* “Sphenophyta: Fossil Record.” ''Fossil Record of the Sphenophyta''

* Stewart, W. N. ''Paleobotany and the Evolution of Plants''. Cambridge University Press, Cambridge (1983). * Davis, Paul and Kenrick, Paul. ''Fossil Plants''. Smithsonian Books (in association with the Natural History Museum of London), Washington, D.C. (2004). *''Calamites''

{{Taxonbar, from=Q11707255 Horsetails Carboniferous plants Permian plants Prehistoric plant genera Carboniferous first appearances Cisuralian genus extinctions Fossils of Georgia (U.S. state) Paleozoic life of New Brunswick Paleozoic life of Newfoundland and Labrador Paleozoic life of Nova Scotia Paleozoic life of Nunavut Paleozoic life of Prince Edward Island Prehistoric plants of North America