Life Cycle of Equisetum (Horsetails): Fertilization, Zygote Formation, and Germination from Gametophyte to Sporophyte

http://premabotany.blogspot.com/2018/12/equisetum.html

Kingdom: Plantae Division/Phylum: Equisetophyta Class: Sphenopsida Subclass: Equisetidae

Orders:

1. Order Equisetales (living horsetails)

   • Family: Equisetaceae
     • Genus: Equisetum
       • Species:
         1. Equisetum arvense, - Field Horsetail
         2. Equisetum giganteum - Giant Horsetail
         3. Equisetum hyemale - Scouring Rush
         4. Equisetum fluviatile - Water Horsetail
         5. Equisetum palustre - Marsh Horsetail
         6. Equisetum telmateia - Great Horsetail
         7. Equisetum variegatum - Variegated Horsetail
         8. Equisetum sylvaticum - Wood Horsetail
         9. Equisetum ramosissimum - Branched Horsetail
         10. Equisetum pratense - Meadow Horsetail
         11. Equisetum laevigatum - Smooth Horsetail
         12. Equisetum scirpoides, - horsetail
         13. Equisetum x ferrissii, Ferriss' Horsetail
         14. Equisetum bogotense, Colombian Horsetail
         15. Equisetum debile - Weak Horsetail
         16. Equisetum diffusum - horsetail
         17. Equisetum moorei, Moore's Horsetail
         18. Equisetum myriochaetum, Large-bristle Horsetail
         19. Equisetum ranunculoides, tuberous-rooted horsetail
         20. Equisetum subgenus Hippochaete, Mexican Giant Horsetail

2. Order †Calamitales (extinct)

Habit and Habitat of Equisetum (Horsetails):

Habit: Equisetum species typically exhibit an herbaceous and perennial habit. They are non-flowering vascular plants that reproduce via spores. The most distinctive feature of their habit is the jointed, hollow stems that arise from rhizomes beneath the soil. These stems are often ribbed and have a rough texture due to the presence of silica.

Habitat: Horsetails are adaptable to various habitats, and different species may be found in diverse environments. The common habitats for Equisetum include:

1. Wetlands: Many horsetail species thrive in wet environments such as marshes, bogs, and along the edges of ponds and lakes.

2. Riparian Zones: Some species are commonly found in riparian areas, growing along riverbanks and streams.

3. Moist Soils: Horsetails often prefer soils with high moisture content, and they can be found in areas with consistently moist or damp soils.

4. Open Fields and Meadows: Certain species, like Equisetum arvense (Field Horsetail), can be found in open fields and meadows.

5. Disturbed Areas: Horsetails are known to colonize disturbed areas, such as roadsides and abandoned fields, where their rhizomatous growth helps stabilize the soil.

6. Woodlands: Some species, like Equisetum sylvaticum (wood horsetail), can be found in wooded areas.

7. Aquatic Environments: Certain horsetail species, like Equisetum fluviatile (Water Horsetail), are adapted to grow in aquatic environments, including shallow water and the edges of ponds.

8. Alpine and Subalpine Regions: In some regions, horsetails can be found at higher elevations in alpine and subalpine zones.

Size Range: The size of Equisetum species can vary, but they generally fall within the range of a few centimeters to over a meter in height. For example, Equisetum hyemale (Scouring Rush) can reach heights of up to 1.5 meters, while smaller species like Equisetum scirpoides (Dwarf Horsetail) may be just a few centimeters tall. Size may also vary based on environmental conditions and habitat.

Plant Body of Equisetum (Horsetails):

The plant body of Equisetum primarily consists of a rhizomatous, jointed stem, which is the dominant structure. The stem is characterized by segmented joints and is responsible for carrying out photosynthesis. Reduced leaves are present in whorls around the nodes of the stem, but they are not the primary photosynthetic organs.

Arthrophytes:

Equisetum belongs to the group of arthrophytes, which are plants characterized by jointed stems. The joints in the stems are a distinctive feature of horsetails, contributing to their segmented appearance.

Leaves:

Leaves in Equisetum are reduced to small, scale-like structures arranged in whorls around the stem nodes. Unlike typical leaves, these structures are not the primary sites for photosynthesis, with the stem taking on this role.

Stele Types with Definition:

The stele is the central cylinder of vascular tissue in a stem or root. Equisetum exhibits a type of stele known as a protostele, characterized by a solid core of xylem surrounded by phloem.

Secondary Growth:

Equisetum primarily undergoes primary growth throughout its life cycle, meaning it increases in length rather than girth. Unlike woody plants with secondary growth, horsetails lack a vascular cambium responsible for producing secondary tissues like wood.

Homosporous and Heterosporous Types with Examples:aaa

• Homosporous:

  • Equisetum species are generally homosporous, producing a single type of spore that develops into a bisexual gametophyte. Example: Equisetum arvense (Field Horsetail).

• Heterosporous:

  • Horsetails are not typically heterosporous. However, some extinct relatives of Equisetum, such as those from the past geological periods, were heterosporous. An example of a heterosporous plant is the club moss, Selaginella.

Sporangiophore:

A sporangiophore is a structure that bears sporangia, the organs that produce spores. In Equisetum, sporangiophores are clustered in cone-like structures called strobili at the tips of the stems. Each sporangiophore bears sporangia that contain spores.

Antherozoids:

The term "antherozoids" refers to male gametes produced by plants for sexual reproduction. In Equisetum, male gametes are produced in structures called antheridia. The antheridia release motile sperm cells, which are involved in the fertilization of eggs in the female gametophytes. These sperm cells are multiflagellated.

Siphonostele with Sclerenchymatous Pith:

Equisetum exhibits a siphonostele, which is a type of stele where the vascular tissue forms a cylinder with a central pith. The pith in Equisetum is sclerenchymatous, composed of supportive cells with thickened walls. The siphonostele provides structural support to the stem.

Internal Structure of Stem:

 

https://www.plantscience4u.com/2016/06/equisetum-stem-anatomy-ts.html

1. Epidermis:

   • The outermost layer of cells that covers the stem.

2. Vallecular Canals:

   • Channels within the stem run parallel to the vascular bundles, providing additional support and aiding in water transport.

3. Cortex:

   • The tissue beneath the epidermis consists of parenchyma cells.

4. Collenchyma:

   • Cells with thickened walls, providing structural support.

5. Sclerenchyma:

   • Cells with lignified walls contribute to the stem's rigidity.

6. Vascular Bundles:

   • Circular arrangements of xylem and phloem tissues that transport water, nutrients, and sugars.

7. Vallecular Canals:

   • These channels are part of the stem anatomy, aiding in the distribution of nutrients and structural support.

8. Pith:

   • The central region of the stem, often parenchymatous, provides support and storage.

Internal Structure of the Leaf (Microphylls):

1. Epidermis:

   • Outer layer of cells covering the leaf.

2. Cuticle:

   • Waxy layer on the outer surface, reducing water loss.

3. Stomata:

   • Pores on the leaf surface for gas exchange.

4. Sunken Stomata:

   • Stomata are located in pits on the leaf surface, helping to reduce water loss.

5. Mesophyll:

   • Tissue between the upper and lower epidermis, where photosynthesis occurs.

6. Vascular Bundles:

   • Contain xylem and phloem for nutrient transport.

Internal Structure of Roots:aaa

 

1. Epidermis:

   • Outer layer of cells covering the root.

2. Cortex:

   • Tissue beneath the epidermis with parenchyma cells.

3. Endodermis:

   • Single layer of cells regulating mineral absorption.

4. Pericycle:

   • Outermost layer of the vascular cylinder, giving rise to lateral roots.

5. Vascular Cylinder:

   • Central region containing xylem and phloem tissues for nutrient transport.

6. Casparian Strips:

   • Bands of impermeable material in the endodermis control the entry of water and nutrients into the vascular system.

7. Root Cap:

   • Protective structure covering the root tip.

Internal Structure of Sporangia:

1. Sporangial Wall:

   • The outer layer of cells protects the spore-containing structures.

2. Spore Mother Cells:

   • Cells within the sporangium undergo meiosis to produce spores.

3. Elaters:

   • Specialized cells aid in spore dispersal, particularly in wet conditions.

4. Spores:

   • Reproductive cells that can develop into gametophytes

Position and Structure of Strobilus in Equisetum (Horsetails):

Position: The strobilus in Equisetum is a cone-like structure that serves as the reproductive organ. It is typically positioned at the tip of a fertile shoot or branch, arising from the main stem. This terminal position allows for efficient spore dispersal.

Structure: The strobilus is composed of multiple whorls of modified leaves, known as sporophylls, arranged in a compact cone. The sporophylls are specialized structures that bear sporangia, the reproductive organs responsible for spore production.

Development of Sporangia:

1. Initiation of Sporangiophores:

   • The sporophylls on the strobilus give rise to structures called sporangiophores, which are stalks that bear sporangia.

2. Sporangium Development:

   • Sporangia develops on the sporangiophores. Each sporangium is a sac-like structure that contains spore mother cells.

3. Spore Mother Cells:

   • Within each sporangium, spore mother cells undergo meiosis, resulting in the production of haploid spores.

4. Maturation of Sporangia:

   • As the spore mother cells mature, the sporangia undergo changes in structure, and the walls of the sporangia become thicker.

5. Elaters Formation:

   • Specialized cells, called elaters, develop within the sporangium. Elaters are hygroscopic, meaning they respond to changes in moisture.

6. Dehiscence and Spore Release:

   • When the sporangia are mature, they undergo dehiscence, which is the process of splitting open. This allows the elaters to assist in spore dispersal. Elaters contract and expand in response to humidity changes, aiding in the release of spores into the environment.

7. Spore Dispersal:

   • Once released, the spores are dispersed by wind or water, contributing to the colonization of new areas.

Structure of Spore:

The spore in Equisetum (horsetails) is a reproductive cell capable of developing into a new individual. The structure of the spore includes:

1. Spore Wall:

   • The outer layer provides protection to the spore.

2. Elater:

   • Specialized, ribbon-like cells with hygroscopic properties. Elaters play a role in spore dispersal by responding to changes in humidity and assisting in spore release.

3. Spore Cytoplasm:

   • The internal contents of the spore, including organelles necessary for the initiation of germination,.

Germination of Spore:

1. Activation:

   • The spore becomes activated, often triggered by factors like moisture.

2. Swelling:

   • The spore absorbs water, causing it to swell.

3. Elater Action:

   • Elaters, responsive to humidity changes, assist in spore dispersal as they expand and contract, aiding in spore release.

4. Germination:

   • The spore undergoes germination, leading to the development of a multicellular structure known as the gametophyte.

Development of Antheridium:

1. Gametophyte Formation:

   • Germination of the spore results in the development of a small, independent gametophyte.

2. Antheridial Initials:

   • Specialized cells, known as antheridial initials, develop on the gametophyte.

3. Antheridial Cell Division:

   • Antheridial initials undergo cell division, giving rise to a structure called the antheridium.

4. Antheridium Maturation:

   • The antheridium matures and produces male gametes called antherozoids.

5. Antherozoid Release:

   • When the antheridium is mature, it releases antherozoids into the environment.

Development of Archegonium:

1. Gametophyte Formation:

   • Similar to the development of the antheridium, the gametophyte forms from the germination of another spore.

2. Archegonial Initials:

   • Specialized cells, called archegonial initials, develop on the gametophyte.

3. Archegonial Cell Division:

   • Archegonial initials undergo cell division, resulting in the formation of the archegonium.

4. Archegonium Maturation:

   • The archegonium matures and consists of a neck and a venter. The venter houses the egg cell.

5. Fertilization:

   • When a water film is present, antherozoids swim to the archegonium. Fertilization occurs when an antherozoid reaches the egg cell within the archegonium.

Fertilization, Zygote Formation, and Germination of Gametophyte to Sporophyte in Equisetum (Horsetails):

1. Fertilization:

   • Fertilization in Equisetum involves the fusion of male and female gametes. Antherozoids, which are male gametes produced in the antheridia, swim through a water film to reach the archegonia, where the egg cell is located.

2. Antherozoid Movement:

   • In the presence of water, antherozoids move actively, propelled by their flagella. They navigate towards the archegonia.

3. Antherozoid and Egg Fusion:

   • An antherozoid successfully reaches the archegonium and fuses with the egg cell inside the venter of the archegonium. This fusion results in the formation of a diploid zygote.

4. Zygote Formation:

   • The zygote is a diploid cell formed as a result of the fusion of the haploid egg cell and the antherozoid. This marks the beginning of the sporophyte generation.

5. Zygote Development:

   • The zygote undergoes divisions and differentiations to form an embryonic structure within the archegonium.

6. Maturation of Zygote:

   • The zygote matures into an embryonic sporophyte while still within the archegonium.

7. Sporophyte Development:

   • The embryonic sporophyte continues to develop within the protective tissues of the archegonium.

8. Germination of Zygote:

   • Eventually, the zygote germinates, leading to the emergence of the sporophyte from the archegonium.

9. Sporophyte Growth:

   • The sporophyte continues its growth and development, ultimately becoming the mature sporophyte plant.

10. Release of Spores:

    • Once the sporophyte matures, it produces sporangia on the strobilus. These sporangia release spores, marking the start of the cycle again.

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       The alternation of generations in Equisetum involves the transition between the haploid gametophyte and the diploid sporophyte phases. Fertilization leads to the formation of a diploid zygote, and the subsequent development of the zygote within the archegonium results in the formation of a new sporophyte, completing the life cycle of the horsetail.