The family Equisetaceae comprises one genus, Equisetum. All around the world, there are close to 15 known species of equisetum. The most commonly occurring species in lowa are Equisetum hyemale (scouring rush) and Equisetum arvense (field horsetail).
The equisetum in the world of Botany is most closely associated with ferns. As seen in ferns, equisetum does not produce seeds, rather reproduce through sexual modes via spore formation. In the spreading of equisetum, however, spores are comparatively not as important.
They give rise to an extensive underground rhizome system expanding across 4 feet or more. Its patches radially extend as rhizomes expand outward from the patch center. The lateral spread of horsetail is comparatively slower in the absence of soil disturbance which pushes the rhizome pieces.
Classification Of Equisetum
Kingdom – Plantae
Class – Polypodiopsida
Order – Equisetales
Family – Equisetaceae
Genus – Equisetum
Form of Growth
Equisetum, commonly addressed to as “horsetails”, possesses a distinct growth form. Their spores are capable of travelling along the ground. They are usually found inhabiting the wet environments and are considered to be semi-aquatic. They exhibit a unique form of growth which sets them apart from ferns. Its uniqueness comes from roots, stems and leaves.
Seemingly, stems of Equisetum take form via the combination of many small segments, resembling the stems of rushes. These stems either project as straight stalks or creep along the ground. These are strengthened with silica and are hollow. This reinforcement causes their stems to stiffen and provides strength.
Leaves of equisetum are seen in a whorl-like appearance with them growing from the same point surrounding the stem. Their branches too, grow in the same pattern. Some of the species possess small scale-like leaves, and most of the time give the impression of being leafless. On the other hand, some species possess slender, long leaves providing the plants with a feathery appearance. Leaves sprout from nodes while the base of leaves is united surrounding the stem creating a collar.
A striking feature of the leaves of Equisetum is the presence of a single vein in the leaves. This trait is shared with lycophytes and this feature in horsetails is believed to have recently evolved.
The rhizomes of the Equisetum species grow much deeper in the surface of the ground. Some of these species possess strobili which are responsible to generate and protect the spores for the purpose of reproduction.
Commonly, this species is not very tall, their average height is close to 2 m. The tallest they can grow is 8 m.
Reproduction In Equisetum
The sporophytes of horsetails reproduce by spore production and vegetative modes.
1. Formation of spores – Spores are formed on strobili or cones, special spore-bearing structures. These cones project individually at the apex of fertile shoots. The primitive kind of cone is a sub-sessile and is apiculate whereas the advanced form of it is stalked with a rounded apex. In some species, annulus (ring-like outgrowth) is seen.
2. Vegetative reproduction – it occurs by two modes –
- Tubers – a round tuber in a few species is developed in rhizomes. When parted from the mother rhizome, the individual tuber goes on to grow into a brand-new plant and hence serving as a mode of vegetative propagation in sporophytes.
- Primordia – each branch possesses preformed branch primordial that develops into aerial branches and subterranean once the old rhizome decays.
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