Tag: introduction to pteridophytes

ln pteridophytes, the diploid sporophyte is represented by a dominant, independent, photosynthetic, vascular plant body. It alternates with multicellular, saprophytic autotrophic, independent but short-lived haploid gametophyte.

The cryptogams are flowerless and seedless plants. They are simple plants including Algae, Mosses and Ferns. They do not produce flowers, fruits and seeds. Cryptogams are considered as lower plants. 

Sphenopsida (like Calamites) were dominant in the Carboniferous period, not the Jurassic.

The body of pteridophytes is differentiated into true stem, leaves and roots like higher plants. They possess well-developed vascular tissues like xylem and phloem for conduction of water and other substances from one part of plant body to another. While the body of thallophytes and bryophytes are not differentiated and lacks vascular system.

The Gnetophyta are a small group of vascular seed plants belonging to the phylum Gnetophyta.
The Gnetophyta include only three genera, Ephedra, Gnetum, and Welwitschia, each of which belongs to a separate family, in a single order, called as the Gnetales. 

Sphenopsida are represented today by the genus Equisetum, so they are not extinct.

Bryophytes are an informal group consisting of three divisions of non-vascular land plants: the liverworts, hornworts and mosses. They are characteristically limited in size and prefer moist habitats although they can survive in drier environments. A bryophyte spore germinates and produces an often algal-like mat, called a protonema (plural protonemata) and the leafy or thalloid stage of the gametophyte develops from the protonemal stage. The protonemata are almost always ephemeral but there are exceptions. Amongst the mosses there is a small number of species in which the protonemata are persistent and the leafy plants are ephemeral. The spore was haploid and so are the resulting protonema and the ensuing leafy or thalloid stages.

Pteris (a fern) and Cycas (a gymnosperm) both produce multiciliated antherozoids.

Most of the algae have dominant gametophyte generations. But in some species, the gametophytes and sporophytes are morphologically similar. An independent sporophyte is a dominant form in all clubmosses, horsetails, ferns, gymnosperms, and angiosperms that have survived to the present day. The gametophyte is dominant in the mosses, liverworts & hornworts only. In mosses, the gametophyte feeds its small attached offspring sporophyte. The mature sporophyte is composed of a "foot" that remains stuck in the gametophyte moss carpet. The sporophyte stands above the moss mat as a long stalk and a capsule that looks like a salt shaker at the tip.
The sporophyte is dominant in all other plants: the ferns, club mosses, horsetails, the gymnosperm (conifers, cycads, ginkgo), and the angiosperm.
In gymnosperm and angiosperm, the entire gametophyte generation is miniature and contained in the cones or the flowers.