Calamites is a genus of extinct arborescent (tree-like) horsetails to which the modern horsetail

Horsetail

Equisetum is the only living genus in the Equisetaceae, a family of vascular plants that reproduce by spores rather than seeds.Equisetum is a "living fossil", as it is the only living genus of the entire class Equisetopsida, which for over one hundred million years was much more diverse and...

s (genus Equisetum) are closely related. Unlike their herb

Herb

Except in botanical usage, an herb is "any plant with leaves, seeds, or flowers used for flavoring, food, medicine, or perfume" or "a part of such a plant as used in cooking"...

aceous modern cousins, these plants were medium-sized trees, growing to heights of more than 30 meters (100 feet). They were components of the understories of coal

Coal

Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

 swamps of the Carboniferous Period (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 sphenophytes, 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 (stems which are preserved in a mineralised form)
• Astromyelon (permineralised rhizomes, distinguished from Arthropitys by the absence of a carinal canal)
• Annularia
  Annularia
  Annularia is a plant fossil from the Carboniferous . It is a form taxon. Its radiating structures are most likely the leaves of Calamites....
  
  and Asterophylites (form genera
  Form taxon
  Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships...
  
   of leaf-whorls which are paraphyletic).

Anatomy

The trunks of Calamites had a distinctive segmented, bamboo

Bamboo

Bamboo is a group of perennial evergreens in the true grass family Poaceae, subfamily Bambusoideae, tribe Bambuseae. Giant bamboos are the largest members of the grass family....

-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

Xylem is one of the two types of transport tissue in vascular plants. . The word xylem is derived from the Classical Greek word ξυλον , meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant...

, meaning they were made of wood. The vascular cambium

Vascular cambium

The vascular cambium is a part of the morphology of plants. It consists of cells that are partly specialized, for the tissues that transport water solutions, but have not reached any of the final forms that occur in their branch of the specialization graph...

 of Calamites was unifacial, producing secondary xylem towards the stem center, but not secondary phloem

Phloem

In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...

.

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

Sediment

Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

. This is the reason pith casts of the inside of Calamites stems are so common as fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s.

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 rhizome

Rhizome

In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...

s, which allowed for the production of clone

Cloning

Cloning in biology is the process of producing similar populations of genetically identical individuals that occurs in nature when organisms such as bacteria, insects or plants reproduce asexually. Cloning in biotechnology refers to processes used to create copies of DNA fragments , cells , or...

s 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

Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...

 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 sediment

Sediment

Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

s. 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

Meristem

A meristem is the tissue in most plants consisting of undifferentiated cells , found in zones of the plant where growth can take place....

 means that this distance varied as the organisms grew.

Extinction and classification

The genus Calamites

Calamites

Calamites is a genus of extinct arborescent horsetails to which the modern horsetails are closely related. Unlike their herbaceous modern cousins, these plants were medium-sized trees, growing to heights of more than 30 meters...

is placed in the family Calamitaceae

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...

 in the plant class Equisetopsida

Equisetopsida

Equisetopsida, or Sphenopsida, is a class of plants with a fossil record going back to the Devonian. They are commonly known as horsetails...

 (formerly known as Sphenophyta) in the fern

Fern

A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...

 allies division Pteridophyta. The Calamitaceae finally became extinct in the Lower Permian

Permian

The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

, a time which also saw the origin and diversification of the herbaceous genus Equisetum, the only living sphenophyte genus.