The family of Equisetaceae comprises one genus called the Equisetum. Across the world, there are around 15 known equisetum species. Equisetum hyemale(scouring rush) and Equisetum arvense (field horsetail) are the most commonly occurring species in Iowa.
In the world of Botany, equisetum is most closely associated with ferns. As seen in ferns, seeds are not produced in the equisetum, it rather reproduces through sexual modes through spore formation. Spores are comparatively not as important in the spreading of equisetum.
They give rise to an extensive underground rhizome system expanding over 4 feet or more. Its patches radially extend like rhizomes expand outward from the patch center. In the absence of soil disturbance, the lateral spread of horsetail is comparatively slower.
Kingdom – Plantae.
Class – Polypodiopsida.
Order – Equisetales.
Family – Equisetaceae.
Genus – Equisetum.
The Life Cycle of Equisetum
Antheridia develop later than archegonia in the monoecious species, They are of two types of antheridium they are projecting type and embedded type. The first appearance of antheridia is on the lobes of the gametophyte. The jacket initial and an androgenic cell gets raised by the periclinal division of the superficial antheridial initial.
A single-layered jacket is formed by anticlinal dividing the jacket initial. The divisions of androgenic cells on a loop from various cells which, on metamorphosis, produce spermatids/antherozoids. Through a pore created by the separation of the apical jacket cell, the antherozoids tend to escape.
The antherozoid's apical part is spirally coiled, whereas the lower part gets expanded to a certain extent. Each antherozoid consists of around 120 flagella attached to the anterior end.
The superficial cell in the marginal meristem acts as an initiation, which undergoes periclinal division and forms a primary cover cell and an inner central cell. By two vertical divisions of the cover cell at a right angle to each other, it forms a neck. The central cell is transversely divided into a primary neck canal cell and a venter cell.
The primary neck canal cell produces two neck canal cells, whereas, the transverse division of the venter cell, forms a ventral canal cell and an egg.
An archegonium of a projecting neck has three to four tiers of neck cells which on maturity gets arranged in four rows, two different neck canal cells, a ventral canal, and an egg. The archegonia are confined in-between the aerial lobes of the cushion region.
Water is an essential component of fertilization. The gametophyte is surrounded by a thin layer of water, where the motile antherozoids swim to reach the archegonia. The neck canal cells and ventral canal cells of the archegonia disintegrate to form a passage. This passage is for the entry of antherozoids.
A number of antherozoids get to pass through the canal of the archegonium, but only one gets fused with the egg. Therefore results in the formation of the diploid zygote. In general, more than one archegonia can be fertilized in a prothallus.
Embryo (The New Sporophyte)
The embryo is called the mother cell and is responsible for the next sporophytic generation. Unlike other pteridophytes, most sporophytes are developed on the same prothallus. The first division of the zygote is transverse and results in an upper epibasal and lower hypobasal cell. The embryo is therefore exoscopic in polarity.
No suspensor can be formed in an Equisetum. The epibasal and hypobasal cells are divided at the right angles to the oogonial wall and this results in the formation of a four-celled quadrant stage, where all the four cells of the quadrant have different sizes and shapes.
The subsequent division of the four-celled embryo, the origin of the future shoot apex, and the remaining cells of the leaf from the quadrant of the epibasal hemisphere.
One cell of the epibasal quadrant and a small part of the adjacent quadrant of the hypobasal region contribute to the development of the root.