By

Sijo.A,

B.Sc Botany & Biotechnology

Equisetum popularly known a the ‘horse-

tail’ or ‘scouring rush’.

It is now represented by nearly 30 species

which are seen world wide except in

Australia and New Zealand.

Some species prefer damp and shady

places while others grow in marshes,

ponds or stream banks

Some are found in xerophytic habitats

Some common Indian species are E. arvense, E. debile, E. elongatum, E. diffusum, E.dubium etc

They are used as indicators of minerals in the soil.Some can absorb gold from the soil.

Deposition of silica on the outer wall of the epidermal cells make the plant surface rough in texture.

By virtue of this property, the plants are often used as abrasives.

Silica forms a protective covering against pathogens and predators

Some species are used in ayurvedic medicines as diuretics.

External featuresThe plant body is differentiated into stem, root

and leaves. It consists of a perennial, prostrate, branched

and creeping underground rhizome from which arise erect and aerial annual branches.

Some of the aerial branches are sterile , whereas some others are fertile.

The aerial branches are usually thin, vine-like and climb over adjacent trees and are herbaceous.

The stem is represented by the much branched, creeping and perennial underground rhizome.

The rhizome is differentiated into nodes and internodes.

At each node there is a whorl of small scaly leaves.

At the axil of each scale leaf, there is a branch bud. It may develop into an aerial or underground branch.

In some species it may form a short and round tuber. On separation from the parent rhizome this tuber develops to a new plant.

The rhizome or stem bears two types of aerial shoots, namely vegetative shoots and fertile shoots.

The vegetative shoots are usually branched, green and photosynthetic.

The fertile shoots are unbranched without chlorophyll and each of them terminates in a cone or strobilus.

At the node o the vegetative shoot, a whorl of lateral branches is present.

The no: of these branches will be equal to the no: of leaves at the node.

These branches are of two types; branches of unlimited growth and branches of limited growth

strobilus

These are similar to the main vegetative shoot. Their growth is unlimited They are branched and differentiatd into nodes and

internodes.

Branches of limited growth They have only limited growth. They are unbranched

and differentiated into nodes and internodes. Due to this the rhizome and aerial shoots have a

jointed appearance. The internodes are hollow and have longitudinal ridges

and grooves. The ridges of successive internodes alternate with

each other. The no: of ridges is equal to the no: of leaves at the node.

Leaves are minute, scaly and isophyllous. They arise in whorls at the nodes of both

underground rhizome and aerial branches They fuse at their base to form a distinct sheath

around the node. Their free distal ends give a frill-like appearance.

The leaves have only a single median vein. Chlorophyll is absent and hence they are non-

photosynthetic. Their main function is to protect the branch buds at

the node. Photosynthesis is carried out by the green and

sterile aerial branches of the rhizome.

All roots of the Equisetum, other than first

or primary root of the embryo are

adventitious.

They are slender and fibrous and arise

either from the node of rhizome or from the

base of upright branches.

They are brached and their branches arise

endogenously from the pericycle.

(1) Anatomy of stem The anatomy of the stem shows both hydrophytic

and xerophytic characters. Also the anatomy of nodes is diferent from that of

internodesa) Anatomy of internode

The T.S of a node is wavy in outline due to the presence of ridges and grooves.

It has distinct epidermis and well-developed cortex and stele, with a ring of vascular bundles and a large central pith cavity.

Epidermis is uniseriate with heavy silica deposition on the outer and radial walls.

Epidermis is interrupted by sunken stomata.The stomatal apparatus consists of four cells,

arranged in two tiers of two cells each.The cells of the lower tier are guard cells and

those of the upper tier are subsidiary or accessory cells.

A series of siliceous thickening bands develop on the lower surface of the accessory cells.

Cortex is differentiated into outer cortex and inner cortex.

Outer cortex consist of sclerenchymatoushypodermis. It is multilayered below the ridges and 1 or 2 layered in the grooves.

Below the stomata there is no sclerenchyma.Sclerenchyma is followed by a band of

chlorenchyma. These cells are photosynthetic in function.

Inner cortex is composed of thin walled parenchyma cells.

Beneath the furrows it has large schizolysigenouscanals, known as vallecular canals.

These canals are are continous in the internodeportion and form a distinct aerating system.

In between the stele and the cortex is the endodermis. It may be single layered or two-layered.

Endodermis is followed by a single layered parenchymatous pericycle.

Vascular cylinder is a siphonostele in which vascular bundles are arranged in a ring around the large pith.

The no: of vascular bundles is equal to the no: of ridges and also to the no: of leaves.

The bundles alternate with the vallecular canals.

The vascular bundles are conjoint, collateral and endarch.

Cambium is altogether absentPhloem is well-developed whereas xylem is

poorly developedProtoxylem consists of annular and spiral

tracheidsMetaxylem consists of scalariform, reticulate

or pitted tracheids. In mature bundles, protoxylem disintegrate to

form a protoxylem lacuna, called carinal canal

Carinal canal forms an inner ring of intercellular spaces. They are filled with water and probably they help in the conduction of water.

Phloem lies outside the xylem in radial arrangement with the carinal canal.It is formed of phloem parenchyma and sieve tubes.

The central part of the internode of the aerial shoot is occupied by a large pith cavity.

The internode has both xerophytic and hydrophytic anatomical features.

Presence of ridges and furrows

Epidermal cells with silica deposition

Presence of sunken stomata

Presence of well-developed

sclerenchymatous hypodermis

Presence of reduced scaly leaves

Photosynthetic stem

Well developed vascular cylinder

Presence of a well developed aerating system, formed of vallecular canals and central pith cavity.

Presence of reduced xylem.

b) Anatomy of nodeThe anatomy of the node differs from that of the

internode in the following features.Pith is not hollow, but it is solid diaphragm,

called nodal diaphragm.Vallecular canals are absent.Carinal canals are absent

Vascular bundles fuse together to form a vascular cylinder around the nodal diaphragm.

Leaf and branch traces arise from the vascular cylinder of the node.

(2) Anatomy of rhizome Anatomically rhizome is almost similar to aerial shoot.

However, it differs from the aerial shoot in the following features.

No stomata in the epidermis Outer cortex has less sclerenchyma Presence of chlorenchyma cells in the cortex Vallecular, carinal and central canals are narrower than

those of the aerial shoot.

Root has three anatomical parts, namely epidermis, cortex and stele.

Root epidermis or piliferous layer is uniseriateand formed of thin walle cells.It is protective in function.

Some epidermal hairs give rise to elongated root hairs.

Cortex is differentiated into sclerenchymatousouter cortex and parenchymatous inner cortex.

Intercellular spaces are absent in the outer cortex but present in the inner cortex

The innermost part of the cortex is the endodermis. It is two-layered.

The cells of its outer layer are large and they posses casparian bands.

A true pericycle is absent in the stelar region. The inner endodermal layer behaves as a

pericycle by giving out lateral roots. In the centre of the stelar region, a protostele is

present, with diarch to hexarch xylem. A large metaxylem tracheid is present in the centre

and the protoxylem strands lie around it. Phloem bundles alternate with xylem strands. Pith is absent.

Apical growth involves the elongation of stem ( rhizome and aerial shoots ) and roots.

The apical growth of the stem takes place by the activity of a large and pyramidal apical cell which has three cutting faces.

It cuts off segments on its three sides. Each segment divides anticlinally forming two

upper and two lower segments Both these segments undergo repeated division,

forming upper and lower tiers of cells. The upper cells give rise to node and thelower

cells give rise to internode.

The apical growth of roots also take place by the

activity of a tetrahedral apical cell which has four

cutting faces, instead of the three in the apical

cell of stem.

The cells cut off from its three lateral faces, form

the epidermis, cortex and stele, and those cut off

from its outer face form the root cap.