Seedless non vascular plants (Phylum Pterophyta)

 Seedless non vascular plants

            (Phylum Pterophyta)

               According to the recent researches, vascular plants are evolved from mosses like plants.  They were the first group of plant those had chance to grown in larger size in the land due to the presence of vascular system. The vascular system arise from the root system further extends into the stem and leaves. It facilitates the efficient way of water and nutrients transport.

             The division Pterophyta can be distinguished from other plant by a vascular system, a dominant sporophyte and dispersal through spores.  Ferns are also restricted to shady moist environments. Most are terrestrial. Some float on the aquatic bodies. Some grow as epiphytes on the tree trunks and rocks in order to get maximum solar energy for maximum photosynthesis. Most of the ferns are found as herbs and shrubs. Tree plants are rarely found such Angiospetris.

             The gametophyte is the short lived one of their life cycles. Their sporophytes and gametophytes are heteromorphic which means both of them are differ in morphology.  Both sporophyte and gametophyte are photosynthetic and can live independently.

             The fern’s sporophyte is much more complex than that of the mosses. The fern sporophyte has vascular tissues. It is well differentiated into the stem, roots and leaves.  The gametophyte is lack of vascular tissues.

             Fern sporophyte has a horizontal underground stem called rhizome with roots emerging from their sides. Some have aerial stem.  The large compound leaves are referred to as fronds. They usually rise from the tip of the rhizome.  Young leaves are called as fiddle heads which appear as rolled up coils. The fiddle heads unroll and develop into the mature leaves.  Most of the ferns fronds are dissected and feathery. Marselia has fronds which is four clovers. But they also develop form the piddle heads.

                  Some ferns possess respectively both of photosynthetic vegetative fronds and Non photosynthetic reproductive fronds that appear in brownish color such as Drymyoglossum. Some have elevated fertile fronds and horizontal vegetative fronds such as Anemia. These elevated fronds bear the clusters of sporangia.  Some ferns possess only vegetative fronds but underside of those vegetative fronds bear clusters of sporangia called as sori. It may or not protected by structure called indusum. In Marseiliea, the microsporangia and megasporangia are produced respectively. Those sporangia are enclosed in special bean shaped structure called as sporacarps.

                  Most Pterophyte are homosporous which produce spores of one size and they result in producing only one gametophyte.  Those homosporous ferns have exosporic development where the gametophyte develops from the outside of the spore wall.  But a significant number of ferns are heterosporous which produce spores of two distinct sizes such tiny microspores and large megaspores.  The microspores produce the male gametophyte and megaspores produce female gametophyte.  Those heterosporous are endosporic development where the gametophyte develops inside the spore wall.

                      The sporangia in the fertile fronds or sorri have thick walled cells on the one side of the sporangium. It is hygroscopic. The diploid spores mother tissues undergo meiosis and produce haploid spores. . Under dry conditions, those hygroscopic cells contract and cause sporangium to release spores. When favorable conditions receive, spores are germinated and result in producing haploid gametophyte.  These gametophytes are heart shaped and in one cell thickness.  They have rhizoid to anchor themselves to the substrate.

                      The flask shaped archegonia and globular antheridia are produced on either side of the same or different gametophyte.  The sperm found in the antheridia have flagella.  When water is present, sperm swim towards the archegonia through a chemical signal released by the archegonia. After fertilization, the diploid zygote is produced. The zygote is developed into the new haploid sporophyte and completes the life cycle. Although ferns also do not produce seeds, they much advanced form the other seedless vascular plants.  Those vascular plants are considered as polysporangiate which means produce sporangia more than one.