NON-VASCULAR PLANTS - BRYOPHYTES

NON-VASCULAR PLANTS - BRYOPHYTES

Division marchantiophyta/hepatocophyta-liverwortsCharacteristicsthey have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of genetic informationestimated that there are 6000 to 8000 species of liverwortstypically small, usually from 220mm wide with individual plants less than 10cm longcertain species may cover large patches of ground, rocks, trees or any firm substrate distributed globally in almost every available habitat, most often in humid locations the most familiar liverworts consist of a prostrate, flattened, ribbon-like or branching structure called a thallus(thallose liverworts)

Lunularia cruciata

most liverworts produce flattened stems with overlapping scales or leaves in two or more ranks, the middle rank is often conspicuously different from the outer ranks (leafy liverworts or scale liverworts)

Plagiochila aspleniodes

Life cycle

The life of a liverwort starts from the germination of a haploid spore to produce a protonema, which is either a mass of thread-like filaments or a flattened thallus. The protonema is a transitory stage in the life of a liverwort, from which will grow the mature gametophore ("gamete-bearer") plant that produces the sex organs. The male organs are known as antheridia and produce the sperm cells. Clusters of antheridia are enclosed by a protective layer of cells called the perigonium.As in other land plants, the female organs are known as archegonia and are protected by the thin surrounding perichaetum. Each archegonium has a slender hollow tube, the "neck", down which the sperm swim to reach the egg cell.

Liverwort species may be either dioecous or monoecous. In dioecious liverworts, female and male sex organs are borne on different and separate gametophyte plants. In monoecious liverworts, the two kinds of reproductive structures are borne on different branches of the same plant. In either case, the sperm must move from the antheridia where they are produced to the archegonium where the eggs are held.The sperm of liverworts is biflagellatethat enable them to swim short distances, provided that at least a thin film of water is present. Their journey may be assisted by the splashing of raindrops. In 2008, Japanese researchers discovered that some liverworts are able to fire sperm-containing water up to 15cm in the air, enabling them to fertilize female plants growing more than a meter from the nearest male.

When sperm reach the archegonia, fertilization occurs, leading to the production of a diploid sporophyte. After fertilization, the immature sporophyte within the archegonium develops three distinct regions: (1) a foot, which both anchors the sporophyte in place and receives nutrients from its "mother" plant, (2) a spherical or ellipsoidal capsule, inside which the spores will be produced for dispersing to new locations, and (3) a seta (stalk) which lies between the other two regions and connects them. When the sporophyte has developed all three regions, the seta elongates, pushing its way out of the archegonium and rupturing it. While the foot remains anchored within the parent plant, the capsule is forced out by the seta and is extended away from the plant and into the air. Within the capsule, cells divide to produce both elater cells and spore-producing cells. The elaters are spring-like, and will push open the wall of the capsule to scatter themselves when the capsule bursts. The spore-producing cells will undergo meiosis to form haploid spores to disperse, upon which point the life cycle can start again.Asexual reproductionSome liverworts are capable of asexual reproduction; in bryophytes in general "it would almost be true to say that vegetative reproduction is the rule and not the exception. For example in Riccia, when the older parts of the forked thalli die, the younger tips become separate individualsA widespread means of asexual reproduction in both liverworts and mosses is the production of gemmae - multicellular bodies that give rise to new gametophytes.Gemmae are dispersed from gemma cups by rainfall. Gemma cups are cup-like structures which the gemma reside in while waiting for rainfall. The gemma cups, when present, are located on the thalli.

Liverworts Marchantia with round cups, and Lunularia with crescent cups, both containing gemmae. Gemmae dislodged by rain are visible at the bottomecologyliverworts can be found in many ecosystems across the planet except the sea and excessively dry environments, or those exposed to high levels of direct solar radiationLiverworts are more commonly found in moderate to deep shade, though desert species may tolerate direct sunlight and periods of total desiccation.they are most common (both in numbers and species) in moist tropical areasClassification

Scientific classification Kingdom: PlantaeDivision:MarchantiophytaStotler & Stotl.-Crand., 1977 emend. 2000Classes and OrdersHaplomitriopsida Stotler & Stotl.-Crand.Haplomitriales (Calobryales)TreubialesJungermanniopsida Stotler & Stotl.-Crand.Metzgeriales (simple thalloids)Jungermanniales (leafy liverworts)Marchantiopsida Stotler & Stotl.-Crand.BlasialesSphaerocarpales (bottle liverworts)Marchantiales (complex thalloids)

division MarchantiophytaClass JungermanniopsidaOrder Metzgeriales (simple thalloids) Order JungermannialesClass MarchantiopsidaOrder Marchantiales (complex-thallus liverworts)Order Sphaerocarpales (bottle hepatics)Order BlasialesClass HaplomitriopsidaOrder HaplomitrialesOrder Treubiales

Economic importance

reduction of erosion along stream bankscollection and retention of water in tropical forestsformation of soil crusts in deserts and polar regionsAquatic thallose liverworts are sold for use in aquariums. Their thin, slender branches float on the water's surface and provide habitat for both small invertebrates and the fish that feed on them.

Marchantia polymorpha, with antheridial and archegonial stalks

Porella platyphylla clump growing on a tree

Pellia epiphylla, growing on moist soil.

Plagiochila asplenioides, a leafy liverwort

Riccia fluitans, an aquatic thallose liverwort.

Conocephalum conicum, a large thallose liverwort.

Division bryophyta

Characteristicssmall, soft plants that are typically 110cm (0.44in) tallcommonly grow close together in clumps or mats in damp or shady locationsdo not have flowers or seeds, and their simple leaves cover the thin wiry stemsat certain times mosses produce spore capsules which may appear as beak-like capsules borne on thin stalks

have stems which may be simple or branched and upright or lax, simple leaves that often have midribs, roots (rhizoids) that anchor them to their substrate, and spore-bearing capsules on long stemsharvest sunlight to create food through photosynthesisdo not absorb water or nutrients from their substrate through their roots, so while mosses often grow on trees, they are never parasitic on the treeabsorb water and nutrients through their leaves

have a gametophyte-dominant life cycle i.e. the plant's cells are haploid for most of its life cycleSporophytes (i.e. the diploid body) are short-lived and dependent on the gametophytethe spore-bearing capsule enlarges and matures after its stalk elongatesLife cycle

Most kinds of plants have two sets of chromosomes in their vegetative cells and are said to be diploid, i.e. each chromosome has a partner that contains the same, or similar, genetic information. By contrast, mosses and other bryophytes have only a single set of chromosomes and so are haploid (i.e. each chromosome exists in a unique copy within the cell). There are periods in the moss life cycle when they do have a double set of paired chromosomes, but this happens only during the sporophyte stage.