Non - Vascular Plants

Non-vascular plants, a category that includes bryophytes and algae, distinguish themselves by the absence of a specialized vascular tissue system for water, nutrient, and sugar transport. Unlike their vascular counterparts, these plants lack true roots, stems, or leaves. Instead, they absorb water and nutrients directly through the surface of their cells. Non - vascular plants include a few algae and members of bryophytes like liverworts, hornworts and mosses. Plants that are non vascular do not have an efficient water transport system thus these plants thrive in moist and cool damp regions. 

1.0Meaning & Definition Non Vascular Plants

Typically, the stature of these plants are short, lacking vascular tissues, true roots, leaves, seeds and flowers. Roots can here be compared to structures called rhizoids which anchor to the ground absorbing water and minerals. Moisture is favourable for their reproduction where sperms produced by the male gametophytes swim through dew or rainwater and arrive at an egg produced by female gametophytes. Spores are produced as a consequence of meiosis of diploid sporophyte generation. Moisture may be required for spore dispersal.

Thallophyta - It is a division of the plant kingdom. It falls under Lower cryptogams. Cryptogams is a greek word, kryptos = hidden & gamos = marriage; hidden sex cells."The flowerless and seedless plants also called as cryptogams".Cryptogam is a group of plant kingdom.

They include Thallophyta ( algae, fungi, lichens ), Bryophytes and Pteridophytes. 

• Lower cryptogams are microscopic plants,containing Thallophyta (algae, fungi and lichens ).
• It comprises Most primitive plants. These are non-vascular plants.
• Plants not differentiated into root stem and leaves. - It comprises Algae, Fungi, Lichens and Bacteria.
• Thallophytes have undifferentiated bodies ( thalli ).
• Plant bodies are filamentous, mycelial and undifferentiated. 
• Plants may be unicellular or multicellular. - Exist almost gametophytic stage and  sporophytes absent or rudimentary. Reproduced by vegetative, asexual or sexual methods.

Thallophyta (ALGAE)

Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely aquatic (both freshwater and marine) organisms. They occur in a variety of other habitats: moist stones, soils and wood. Some of them also occur in association with fungi (lichen) and animals (e.g., on sloth bear).The form and size of algae is highly variable, ranging from colonial forms like Volvox and the filamentous forms like Ulothrix and Spirogyra . Some of the marine varieties like kelps, provide massive plant bodies.  The algae reproduce in three ways: vegetative, asexual and sexual. Vegetative propagation is through fragmentation. One fragment develops into a thallus. For asexual reproduction the varied forms of spores formed, the most frequent, being the zoospores are formed. They are motile flagellated in germination they produce new plants. For sexual reproduction occurs through the union of two gametes. These gametes may be flagellated and of equal size (such as in Ulothrix) or non-flagellated (non-motile) but of the same size (as in Spirogyra). Such reproduction is known as isogamous. Union of two gametes of different sizes, such as in species of Eudorina is called anisogamous. Union between a large, nonmotile (static) female gamete and a smaller, motile male gamete is called oogamous, e.g., Volvox, Fucus

Algae are useful to man in a variety of ways. At least a half of the total carbon dioxide fixation on earth is carried out by algae through photosynthesis. Being photosynthetic they increase the level of dissolved oxygen in their immediate environment. They are of paramount importance as primary producers of energy-rich compounds which form

the basis of the food cycles of all aquatic animals. Many species of Porphyra,Laminaria and Sargassum are some of the 70 species of marine algae used as food. Some of the marine brown and red algae yield huge quantities of hydrocolloids (water holding substances), e.g., algin (brown algae) and carrageenan (red algae) which are commercially employed. Agar, one of the commercial products obtained from Gelidium and Gracilaria, are used to grow microbes and in preparations of ice-creams and jellies. Chlorella, a unicellular alga with high protein content is used even as a food supplement by astronauts. Algae are of three main classes: Chlorophyceae, Phaeophyceae and Rhodophyceae.

Some commonly found green algae are: Chlamydomonas, Volvox, Ulothrix, Spirogyra and Chara.

The common forms of brown algae are Ectocarpus, Dictyota, Laminaria, Sargassum and Fucus.

The common members of red algae are: Polysiphonia, Porphyra , Gracilaria and Gelidium.

Bryophyta

Bryophytes are known as the amphibians of the plant kingdom because  these plants can live in soil but remain dependent on water for sexual reproduction. Generally, they occur in damp, humid and shady localities. They often play an important role in plant succession on bare rocks/soil. The plant body of bryophytes is more differentiated as compared to that of algae. It is thallus-like and prostrate or erect, and attached to the substratum by unicellular or multicellular rhizoids. They lack true roots, stems or leaves. They may possess root-like, leaf-like or stem-like structures. The main plant body of the bryophyte is haploid. It produces gametes, hence is called a gametophyte. The sex organs in bryophytes are multicellular.

The male sex organ is called antheridium. They produce biflagellate antherozoids. The female sex organ called archegonium is flask-shaped and produces a single egg. The antherozoids are released into water where they come in contact with archegonium. An antherozoid fuses with the egg to produce the zygote. Zygotes do not undergo reduction division immediately. They produce a multicellular body called a sporophyte. The sporophyte is not free-living but attached to the photosynthetic gametophyte and derives nourishment from it. Some cells of the sporophyte undergo reduction division (meiosis) to produce haploid spores. These spores germinate to produce gametophyte.

Bryophytes in general are of little economic importance but some mosses provide food for herbaceous mammals, birds and other animals. Species of Sphagnum, a moss, provide peat that have long been used as fuel, and as packing material for trans-shipment of living material because of their capacity to hold water. Mosses along with lichens are the first organisms to colonise rocks and hence, are of great ecological importance.

They decompose rocks making the substrate suitable for the growth of Higher plants. Since moses form dense mats on the soil, they reduce the impact of falling rain and prevent soil erosion. Bryophytes are found commonly growing in moist shaded areas in the hills.The bryophytes are divided into liverworts and mosses.

• These are non-vascular plants.They are higher cryptogams.
• They are the most simple and primitive plants. Plants are thalloid and multicellular.
• plant body gametophyte, green and dominant. Habitat-aquatic or terrestrial or amphibians. 
• Nutrition- Autotrophic mode of nutrition.
• Reproduction by vegetative, sexual and asexual methods.
• Gametes developed on the gametophyte.
• Fertilization-male and female gametes unite to form zygote.
• Water is an important medium for fertilization.
• Zygote undergoes repeated division and forms a sporophyte, which produces spores.
• Haploid spores on germination produce gametophyte.
• Life cycle shows alternation of generations.
• Gametophytic and sporophytic generations alternate with each other to  complete the life cycle. Gametophytes are dominant and independent whereas sporophytes are dependent. eg. Riccia, Marchantia etc

Liverworts- They grow in small, leaf-like structures and are primitive non-vascular plants. They thrive in swampy, shady, and damp places closer to the ground. They typically thrive in tropical areas although they are distributed widely. The gametophytic structure of this plant is thallus which develops specialized structures to harbor the sporophytic phase. Common examples are Porella,Riccia and Marchantia.

Moss- They range from being a foot tall to microscopic and are found in most dark and swampy areas and other environments. They are found on forest floors and carpet woodlands. Close to 12,000 species of mosses are known globally colonizing habitat ranging from desert lands to cold arctic areas. Lack of vascular tissues hampers their growth, or in other words height-wise, as a result, transportation of mineral and water all the way to the top portion of the plant is not seen.Common examples of mosses are Funaria, Polytrichum and Sphagnum.