Tag: classification of pteridophytes

In Pteridophyte Dryopteris the gametophytes give rise to sporophyte by gametic union and sporophyte gives rise to gametophyte by forming haploid spores after meiosis. 

The multiflagellated antherozoids of Dryopteris, point out that they originated from aquatic ancestors. In auatic environment the multiflagellated antherozoids swim in the water and fertilize the egg. Water is necessary for the fertilisation process. It proves their aquatic ancestry.

The polycyclic condition is the most complex of stelar organization found among pteridophytes. It is a dictyostele consisting of two or more concentric rings of meristeles. It occurs in Pteridium sp. 

Young sporophyte of Pteris draws nourishment from the foot. Foot is formed first, which absorbs water, minerals from prothallus. Prothallium, or prothallus is usually the gametophyte stage in the life of a fern or other pteridophyte. The prothallium develops from a germinating spore. It is a short-lived and inconspicuous heart-shaped structure typically 2-5 millimeters wide, with a number of rhizoids (root-like hairs) growing underneath, and the sex organs: archegonium (female) and antheridium (male). Appearance varies quite a lot between species. Some are green and conduct photosynthesis, while others are colorless and nourish themselves underground as saprotrophs. 

Dryopteris species can be identified by the circular shaped sori, that is covered by a kidney-shaped, translucent tissue. It is called as indusium. It is a shield like outgrowth of the leaves.

The class Pteropsida is characterized by pteridophytic plants, that have large, dissected leaves and sporangia, that are borne on the leaves. Pteropsida is divided into three classes - (i) filicineae, (ii) gymnespermae, (iii) angiospermae. 

Some epidermal cells give rise uniseriate bicellular brown hairs on young leaves of Pteris or any other fern, called as ramenta. 

In the male gametophyte of Selaginella, the single prothallial cell is the only vegetative structure, as the rest of the cells develop into the antheridium.

The sperm of Selaginella are attracted to the archegonia by chemical substances, specifically malic acid, which is a common chemotactic agent in pteridophytes.

Dryopteris, is a genus with more than 250 species and is widespread in the temperate zones in northern hemisphere. The diploid sporophyte and haploid gametophyte of Dryopteris regularly alternate with each other. The haploid spore which gives rise to the gametophyte which is the monoecious prothallus and bears sex organs on its ventral side. After fertilization, they give rise to the sporophyte which is the dominant asexual member in the life cycle of the plant and is a perennial evergreen, differentiated into rhizome (stem), roots and leaves. Hence, both the gametophyte and sporophyte are independent of each other.