2 LITERATURE REVIEW
2.1 Morphology of Liverworts
Liverworts are an ancient and belong to the oldest land plants. They existed already in the Palaeozoic period in forms which were hardly different from the
extant species. They remained relatively unchanged with relatively low evolution rates, and are thus often called a “conservative“ plant group Frahm 2003.
Liverworts are non vascular plant without vessels, attached to the substrate by rhizoids do not have roots, and without cuticle and stomata on their
leaves. The process of transporting water and minerals in the body takes place in diffusion and assisted by the flow of cytoplasm. Due to the lack of roots, stomata
and cuticle leaves, make them as typically poikylohydric plants, or easy to absorb and emit water, that is, their turgor depends on moisture in the environment.
During dry periods, the plants dry up almost completely and may become dormant. When wetted, water is taken up rapidly by plants Gradstein et al. 2001.
Liverwort life cycle have an alternation of two phases or generations, a sporophyte and a gametophyte. The dominant generation in the life cycle is the
gametophyte, which originate from a spore produced by the sporophyte. Sporophyte is comparatively short lived and nutritionally depent on the free-living
gametophyte. The sporophytes also completely mature in gametophytic body Stotler and Stotler 2000; Gradstein et al. 2001.
Liverworts are small in size but they can be very conspicuous growing as extensive mats in woodland, as cushions on walls, rocks and tree trunks, and as
pioneer colonists of disturbed habitats. They are very diverse in structure and
often with highly variable morphology. There are two types of liverworts based on body form: thallose and leafy liverworts.
2.1.1 Thalloid liverworts
Thalloid liverworts have a dorsiventrally flattened gametophyte or thallus, ribbon-like, dichotomously branching structure pinnate in Riccardia. They are
not divided into stem and leaves and variable in its structure. Thallus surface that contact with the substrate is called the ventral surface while the other is called the
dorsal part. Many rhizoids and sometimes many scales are found on the ventral surface. Tissue within the thallus can be quite differentiated or have little
differentiation. There are two types of thalloid liverwort: simple thalloid and complex thalloid. The simple thalloid liverworts have undifferentiated thallus
composed of one or two cell layers, all cells are green and filled with chlorophyll and oil bodies. The simple thalloid liverworts are clasified in Metzgeriales, for
example: Metzgeria, Pallavicinia and Riccardia. The structure of complex thalloid are divided into ventral and dorsal side. The ventral side have colorless
tissue, for saving metabolites and often contains specialized oil cells. The dorsal side have green tissue in which contain air chambers that open by pores to the
upper thallus surface. The dorsal side have green tissue, contains The complex thalloid liverworts are clasified in Marchantiales: Marchantia and Dumortiera
Gradstein et al. 2001; Gradstein 2011.
The antheridia and archegonia of thalloid liverworts are produced on the dorsal of thallus surface, inside the thallus, or on swollen organ called receptacles.
The stalked of female receptacle is called as archegoniophore and the stalked of male receptacle is called as antheridiophore Gradstein 2001.
2.1.2 Leafy liverworts
The stem of liverworts are rather thin, simple or variously branched. There are two basic types of branches: intercalary and terminaly branches. In general,
leafy liverworts have two or three rows of leaves, two lateral rows lateral leaves and one ventral row underleaves. The lateral leaves position may be transverse,
incubous, or succubous. Incubous leaves have dorsal leaf margin lies on top of the ventral margin of the younger leaves. It is just the other way around in succubous
leaves. The leaves are only one cells thick, lack a midrib or costa. The leaf cells vary in shape and often have collenchymatous thickenings called trigones. The
cells usually have chloroplasts and oil bodies when fresh. The characteristics of oil body such as number per cell, size, and structure are taxonomically important
in identification of the majority of liverworts taxa The underleaves are usually smaller than the lateral leaves and sometimes lacking Gradstein et al. 2001;
Gradstein 2011.
2.2 The Ecological and Economic Importance of Bryophytes
The bryophytes were thought to have no use since they are inconspicuous and have small size. However, bryophytes are used for many purpuse, such as
horticulture, household, medicine, and they have ecological
importace.
2.2.1 Bioindicators
Liverworts and mosses have been found to be good indicators of environmental conditions. The suitability of liverworts as bioindicators is mainly
due to the lack of conductive tissues and do not have a protective leaf cuticle. Consequently, gasses and solutions entrance freely to the living cells of
bryophytes. The structure without cuticle could easily to intake the water and minerals including heavy metals. Their sensitivity to environmental changes and
air pollution make them as a good bioindicator of environmental conditions, disturbances in ecosystem, and climatic changes. They absorp pollutants through
the leaf or thallus directly from the atmosphere or water and accumulate them in large amounts Gradstein et al. 2001.
Some bryophytes grow only in a narrow and specific pH range, therefore they could be used as an indicator of soil pH. Some aquatic species are indicator
for calcium and other nutrient content in water as well as water pollution. The liverworts have also been used to monitor air pollution caused by emissions from
various sources. They could absorb and retain pollutants in higher quantities than those absorbed by other plants in the same habitat Saxena and Harinder 2004.
The role of liverworts as indicators of environmental changes have been reported in various types of landscape Holz and Gradstein 2005; Drehwald 2005;
Larsen et al. 2007. Some bryophytes are metal tolerant and able to withstand levels of heavy metals that are toxic to other species. Heavy metals are absorbed
from the atmosphere or the substrate. Marchantia polymorpha, Solenostoma crenulata
, are the example of the metal tolerant populations. Scapania undulata is used to monitor water pollution Govindapyari et al. 2010.
Some other species of bryophyte have also been used as indicator of air pollution caused by people
activities in residential areas, polluted by fumes or industry Dymytrova 2009. 2.2.2 Pioneer plants and erosion control
Bryophytes have capability to rapidly colonize substrate, therefor they are pioneer plants in bare lands. Thick layer of bryophyte on soil may have ability to
absorb and store a large quantities of rain water, and prevent soil erosion Gradstein et al. 2001. The ability to reduce erosion have important role,
especially on the outskirts of the newly opened road and the slope of the hill, before the larger plants are growing. Bryophytes also has potentially role in
helping revegetation of degraded land, for example in the former mining areas, clearing land, and forest conversion. This capability is supported by the ability of
bryophytes to form a large population or a vast expanse quickly Glime 2007b.
2.2.3 Habitat for other organisms
Bryophytes may offer shelter to small animals. Epiphytic liverworts are widely used as habitat by insects such as ants, beetles, and mites. The insects also
used the bryophytes for storing their larvae. Small animals such as lizards, snails, frogs, and arthropods are frequently found on the terrestrial liverworts mats. They
used the liverworts to create moist environment, protect them from the wind, and for laying their eggs. Liverworts can accumulate organic matter and dust, making
it possible to accomodate food source for the small animals. Liverworts also may serve as substrate for other plants Glime 2007a.
2.2.4 Horticultural uses
Bryophytes have been involved in horticulture as soil additives, ground cover, greenhouse crops, ornamental of potted plants, and for seedling beds.
Bryophytes are often used to conditionize and fertilize the soil. Coarse textured of bryophytes increase water-storage capacity. They may improve the nutrient
condition by holding nutrients, especially those borne by dust and rainfall, and releasing the nutrients to the soil surface. Recently, one of the more important
functions of the liverwort is in the study of the physiology and genetic potential in gene transplantation for traits tolerant to drought and as antiherbivora for
agricultural crops Glime 2007b
. .
Many species of liverworts may contain natural pesticides, for example: the species of Plagiochila contains the sesquiterpene hemiacetyl plagiochiline A, a
poison extremely potent in mice, and it inhibits the feeding of an African army worm. Extracts of Frullania brasiliensis can inhibit the growth of fungal
pathogens on vegetables such as tomatoes and potatoes. Asakawa et al. 1980.
2.2.5 Medicine One reason in the bryophyte exploitations is the biological compounds that
can be used for medicine. Liverworts are used in traditional medicine for treating some diseases such as liver, hookworm, swelling, fever, digestive and urinary
problems, infections, lung, and skin diseases. The traditional use of liverworts
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