Equisetum

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Introduction

All over the world, there are 15 known species of the equisetum. Some of the commonly occurring species in Equisetum hyemale commonly known as scouring rush and Equisetum arvense are known as field horsetail. In the world of botany, the equisetum is more closely located with the ferns. But there is some difference between ferns and the equisetum, like the equisetum does not produce seed, rather it reproduces through sexual modes by the formation of spore. 

Equisetum gives rise to many underground rhizome systems, which expands near to four feet or more. Equisetum patches extend radially as rhizomes outward from the patch centre. The spreading of horsetail is laterally slower in comparison to the absence of soil disturbance which pushes the rhizome pieces. 

Equisetum stem is formed by the combination of many small segments, resembling the stems of the rushes; they either project as a straight stalk or creep along the ground. These stems are hollow and are strengthened with silica, the reinforcement helps their stem to stiffen and provides strength.


Equisetum Classification  

Scientific classification of equisetum is given below - 

Kingdom – Plantae

Class – Polypodiopsida

Order – Equisetales

Family – Equisetaceae

Genus – Equisetum


Reproduction in Equisetum 

Equisetum reproduces in two ways one is vegetatively and the other is by the means of spore, let us see in brief about each below -

Vegetative Reproduction - It occurs in two modes tubers and primordia. Subterranean rhizomes of some species like E.telmateia, E.arvense form tubers. Which on separation from the parent plant, germinate to produce new sporophytic plants. The tubers developed due to the irregular growth of some buds at the nodes of the rhizomes. Primordia occur in each plant processing pre-formed branch primordial that develops into aerial branches and subterranean once the old rhizome decays.

Reproduction By Spores - In this the spores are produced within the sporangia, and they are borne on the sporangiophores which are aggregated into a compact structure termed as strobilus or cone or sporangiferous spike. 


Equisetum Strobilus 

Equisetum strobilus is also known as the equisetum cone. Generally, they are terminal in position and borne terminally on the chlorophyllous vegetative shoot. But they can also be born terminally on a strictly non-chlorophyllous axis, an example of this type is E.arvense.

Strobilus is composed of whorls of sporangiophores in an axis. Sporangiophore is a stalked structure bearing a hexagonal peltate disc and its distal end, a disc from five to ten elongated cylindrical hanging sporangia. And they are born near the periphery in a ring. 

The flattened tips of the sporangiophores will fit closely together, to provide protection to the developing sporangia. The axis bears the ringlike outgrowth called the annulus and it immediately forms the whorl of sporangiospores, which provides additional protection during the early development. This annulus will be interpreted as a rudimentary leaf sheath by some botanist. And others considered it as sporangiophore in nature, as occasionally it bears the small sporangia. 


Life Cycle of Equisetum

In the life cycle of equisetum, there are two important sex organs, antheridium and the archegonium

Anthredium - Anthredia will develop into archegonia, In the monecious species. There are two types of archegonia projecting type and the embedded type. Anthredia first appears on the lobes of the gametophyte, and the periclinal division of the superficial anthredial initially gives rise to a jacket initial and an androgonial cell. The jacket initiated will divide anti clinically to form a single-layered jacket. When the androgonial cells divide repeatedly to form numerous cells. These cells on metamorphosis produce spermatids or antherozoids. The antherozoids escape through the pore created by the separation of the apical jacket,  the apical part of the antherozoid is spirally coiled and the lower part is extended to some extent.

Archegonium - The superficial cell in the marginal meristem acts as the initiation of the archegonium, which undergoes periclinal division to form a primary cover cell and an inner central cell. The cover cell, of the two vertical divisions at a right angle to each other, forms the neck and the central cell divides transversely to form a primary neck canal cell and a venter cell. Two neck canal cells are formed from the primary neck canal cell and the white venter cell formed by the transverse division and they form the ventral canal cell and an egg. During maturity, archegonium has a projecting neck consisting of three to four tires of the neck cell arranged in four rows. Having two neck canal cells of unequal size, a ventral canal cell, and an egg at the base of the embedded ventre. 

Fertilization - Water is very essential for fertilization, the gametophyte is covered in a thin layer of water in which motile antherozoids swim to archegonia. Archegonia’s neck canal cells and the ventral canal cell will disintegrate to form a passage for the entry of antherozoids. Many antherozoids pass through the archegonia, but only one among them fuses to form a diploid zygote. 

Embryo -  It is the next stage of the sporophytic generation, the embryo is the mother cell. These sporophytes develop on the same prothallus and the first division of the zygote is transverse. This results in the upper epibasal cell and the lower hypobasal cell therefore the embryo is exoscopic.  These both the cells divide at the right angle to the oogonial wall which results in the four celled quadrant stage being established. In this, all four cells are of different size and shape. On the further division of the four celled embryo, it forms the shoot apex and leaf initials in the future. Further, the root grows directly downward and penetrates the gametophytic tissue to reach the soil.  


Conclusion 

After going through in detail about equisetum like classification, reproduction and life cycle of equisetum, we understood how reproduction takes place in this species and some of the basic details about shape, size, colour, and finally the types of reproduction. Actually, equisetum species can be used as herbs, to improve the health of the skin and hair. It has a mild grass-like flavour, which can be consumed along with other herbs in the tea.  

FAQ (Frequently Asked Questions)

1. Is Horsetail Poisonous to Humans?

Answer. No, horsetails are not poisonous to humans. But they are poisonous to the horse and the livestock. Equisetum palustre is the chemical found in horsetails that is poisonous to herbivorous animals, but not to humans.

2. What Does Horsetail Look Like?

Answer. The leaves are arranged in a form of whorl fused into the nodal system. The stem of these species are green and photosynthetic and are distinctive in being hollow, jointed and rigid. Most of the species of the horsetail grow to a height of one to five feet tall and the giant horsetail can grow to a height of 26 feet tall.