What is Equisetum ?

Plant body is differentiated into stem, leaves and roots. Height is from a few centimetres to several metres. Stem has two components, underground rhizome and upright aerial branches. Stems are jointed. Internodes possess longitudinal ridges or ribs and hollow interiors. Nodes possess a whorl of scale leaves. Function of photosynthesis is carried out by green aerial stem branches. Intercalary meristem occurs above the nodes. In rhizome some of the branch primordia develop into tubers, e.g., E. arvense. Due to presence of intercalary meristems, internodes can be easily pulled out as pipes.

Adventitious roots develop in whorls over the nodes of rhizome. Xylem has xylem vessels. Aerial branches develop terminal strobili. In E. arvense, there are two types of aerial branches, green sterile and brown fertile. Terminal strobili occur only on fertile branches.

Pteropsida (Ferns). The most conspicuous of the pteridophytes are the ferns. Ferns are pteridophytes that bear sporangia in sori on the leaves which show circinate ptyxis in the young condition.

Sporophytic plant body of Equisetum arvense showing underground rhizome bearing roots,fertile and sterile Aerial branches and tubers :👇🏻

1. The stem is underground rhizome in most of the ferns. Some primitive ferns above-ground stem with tree-like habit. They are called tree ferns, e.g., Cyathaea, Celeotium. A tree fern is like a small palm. It may reach a maximum height of 20 m.

2. Leaves are large and are called fronds. They are often graceful. Leaves may be simple or pinnately compound. In a pinnately compound leaf, the lamina is divided laterally into leaflets. It may be unipinnate (once pinnate, leaflets borne directly on rachis which is continuation of petiole), bipinnate (twice pinnate, leaflets borne on primary branches of rachis) or tripinnate (thrice pinnate, leaflets borne on tertiary axes or secondary branches of rachis).

3. Leaves or their leaflets show open furcate venation in which veins branch dichoto-mously without forming interconnections.

4. Younger parts of stem, young leaves, petiole and rachis of mature leaves possess hairs or scales called ramenta. Ramenta protect them from mechanical injury and desicca-tion.

5. The gametophyte is thalloid and called prothallus. Prothallus is the term used for free living gametophyte having sex organs. It develops a young sporophytic plant body from inside the female sex organ.

6. The life cycle has a regular alternation of a dominant sporophyte and an inconspicu-ous gametophyte. This is called heterologous or heteromorphic alternation of generations.

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