INTRODUCTION
Manju C. Nair “Eco-systematic studies on bryophytes of Wayanad, Kerala”
Thesis. Department of Botany , University of Calicut, 2005
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"I carried a basket for mosses and gathered some wild plants.
Oh! That we had a book of botany"
Dorothy Words worth ..
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1. INTRODUCTION
Bryophytes are a diverse and distinct group of primitive plants, with about
25,000 species distributed the worldover, making it the second largest group of
land plants next to the flowering plants. They are considered as "amphibians of
plant kingdom" owing to their preference to aquatic and other wet habitat.
Bryophytes are characterized by the absence of vascular tissues and having a
unique life cycle with a dominant gametophyte generation except in few genera
such as Buxbaumia. The sporophyte, which produces the spores, is dependent
on the gametophyte for existence. The group includes three distinct lineages
viz., liverworts, hornworts and mosses. They inhabit in a variety of microhabitats
from the human habitation to higher altitude areas which includes soil
(terrestrial), bark (epiphytic), leaves (epiphylls), rock (lithophytes) and water
(aquatic). The diversity and frequency of bryophytes are maximum in the shady
and wet regions compared to the open areas. The bryophytes are generally
considered as a key group in our understanding of the phylogenetic
interrelationship of modern land plants and pioneers in conquering the land with
an environment hostile from their primitive home in fresh water.
1.1. ORIGIN AND EVOLUTION
Among extant embryophytes, bryophytes exhibit a series of traits suited
similar to the aquatic habitat and thus appear as first batch for making the
transition to land. The origin of bryophytes and their relationship to early land
plants have been explained from the fossil records. The ancestors to land
plants, particularly of fresh water origin were mostly growing close to a
terrestrial habitat and thus exposed to temporal water level fluctuations. Such
species could have overcome exposures to the aerial environment by
developing drought resistant spores. The presence of cryptospores in
sediments of Mid-Ordovician shows that the spores are arranged in permanent
tetrads, a feature characteristic of land plants (Kenrick & Crane, 1997a). Some
cryptosporic
tetrads
are
reminiscent
of
bryophytes,
such
as
the
Sphaerocarpales (Gray, 1985). The ultrastructure of spore walls of Dyadospora
sp. and Sphaerocarpalean liverworts (Taylor, 1996) give evidence to the
hypothesis that at least some of the early land plants have affinities with the
liverwort lineage. The presence of trilete spores in the Lower Silurian period,
shows
bryophyte affinities, since trilete marks occur on spores of
representatives of hornworts, liverworts, mosses and other land plants (Taylor,
1982). Cook and Graham (1998) suggested that Charophyceae and bryophytes
have surface layers similar to the cuticle of vascular plants.
Except for Torticaulis transwalliensis the megafossils from the Mid to
Upper Silurian exhibit no affinities to bryophytes and are related to vascular
plants but with uncertain relationship (Kenrick & Crane, 1997a). The
Sporogonites from Lower Devonian of Norway and Belgium consists of long,
erect and unbranched axes bearing terminal sporangia similar to extant
hepatics and the moss Takakia (Halle, 1916, 1936; Goffinet, 2000). Moreover,
Sporogonites has a columella-like projection (Halle, 1936) a feature present in
hornworts
and
primitive
mosses
Sphagnopsida,
Andreaopsida
and
Takakiopsida (Schofield, 1985). But the systematic position of Sporogonites and
thus its significance in the evolution of bryophytes remain uncertain (Kenrick &
Crane, 1997b).
Hepaticites devonicus (Hueber, 196 1) is the oldest unequivocal fossil
bryophyte dates from the Upper Devonian and this plant is similar to the extant
taxon, Pallavicinia. The earliest record of the moss in the fossil record is
Muscites plumatus which could be from the Lower Carboniferous (Thornas,
1972), other fossils such as Muscites polytrichaceous and M. bertrandi are from
the Upper Carboniferous (Krassilov & Schuster, 1984). The ornamentation of
the Paleozoic spores Streelispora and Aneurospora has been compared to that
of Anthoceros, and used as evidence to support the presence of bryophytes in
the Silurian (Richardson, 1985). Eventhough the fossil record offers valuable
insights into the taxonomic diversity of the early land plant flora, it fails to offer
supportive evidence for the presence of bryophytes among early plant lineages
(Goffinet, 2000). The lack of complexity and haplo-diplobiontic life cycle
however, suggest that bryophytes compose a rather basal lineage of land
plants.
The antithetic and homologous theories of evolution of land plants
discusses the relationship of bryophytes and its origin. Bryophytes shows a
peculiar feature where the sporophyte is short-lived and attached to the
dominant gametophyte. The gametophyte is free-living and the biflagellate male
gametes require a film of water to reach archegonia. These reproductive
constrains point to an aquatic ancestry and thus to the possible significance of
bryophytes in the phylogeny of land plants. Hofmeister (1851) proposed that the
life cycle of plants is composed of two phases, a gametophyte bearing sexual
organs and a sporophyte producing spores, and that these fundamental phases
are homologous among plants. Celakovsky (1874) examined Hofmeister's
observations in an evolutionary context, and his hypotheses were later
developed into antithetic or interpolation theory (Bower, 1890, 1908). This
theory proposes that land plants arose from an algal ancestor with a
haplobiontic life cycle, composed of heteromorphic phases, a multicellular
gametophyte and a unicellular sporophyte. In bryophytes the sporophyte would
remain attached to and at least in part nutritionally dependent on the
gametophyte. Increase in mitotic divisions would allow for additional growth in
body size of the sporophytes for more complex tissues to develop and there by
giving rise to early vascular plants. In this scenario, bryophytes or an organism
allied to them represent the ancestor to the line that give rise to the
tracheophytes. The fossil record however does not provide unambiguous
evidence in support of this hypothesis.
In contrast to antithetic theory, the homologous theory (Pringsheim,
1878) suggests that the ancestor to land plants had two isomorphic,
independent and thus autotrophic phases. The central point of the homologous
theory is that from an ancestor with isomorphic gametophyte and sporophyte,
two divergent lines of evolution with variant dominant phases are formed. Here
the dominant phase varies. In the first line, leading to the bryophytes, the
sporophyte underwent reduction while the gametophyte become more complex.
In contrast, the pteridophytes would have arisen by amplification of the
sporophyte at the expense of the gametophyte. Although the proponents of this
theory still consider bryophytes and pteridophytes are related (Zimmerman,
1932), the latter would have arisen independently from the former. From this it
is clear that bryophytes had no significance regarding the evolution of
polysporangiophyta.
It is also evident that these two alternative theories are inconsistent.
Even within the antithetic theory, a direct transition from a gametophyte
dominated life cycle to a sporophyte dominated one appears (Kenrick, 1994).
A charophycean ancestry of embryophytes suggests that the multicellular
sporophyte of land plants arose de novo, as meiosis is delayed by interpolation
of mitotic divisions. The multicellular sporophyte evolved through interpolation of
mitotic divisions prior to sporogenesis. Recent phylogenetic reconstruction of
relationships among extant lineages of land plants converge toward a
hypothesis where the hornworts compose the most basal group, with the moss
and liverworts forming a monophyletic clade sister to the polysporangiophytes.
The interpretation of the fossil from Devonian reveal the early land plants are
characterized by nearly isomorphic gametophytes and sporophytes. This
revived the hypothesis that bryophytes may have evolved from such forms, and
thus, that the sporophytes of bryophytes is the result of reduction through the
loss of the ability to branch and to develop multiple sporangia (Goffinet, 2000).
Based on recent morphological cladistic analyses, the classical group
"bryophytes" appears not to be monophyletic. Instead, the mosses seem to be
more closely related to the vascular plants than to the hornworts or liverworts
(Mishler & Churchill, 1984, 1985; Bremer et al., 1987). Even more recent
molecular cladistic analyses confirm the non-monophyly of the bryophytes, and
the relatively basal position of the liverworts, although the precise
interrelationships of the mosses, hornworts and tracheophytes remain
problematic (Mishler et al., 1994).
1.2. SIGNIFICANCE OF BRYOPHYTES
Eventhough there are no direct uses for bryophytes, they are ecologically
significant as playing a key role in ecosystem dynamics. In recent years the
studies on the various applied aspects of bryophytes have come to light
particularly on horticultural value, utilization as medicine, as seed bed for higher
plants, as rock and mineral builders, use as bioindicators (Ando & Matsuo,
1984), in ecosystem nutrient dynamics, in pollution detection (Bates, 2000) and
on global carbon budget (Neill, 2000).
1.2.1. Horticultural uses
Horticulturalists and landscape architects have found them valuable,
particularly the peat moss, for the construction of moss gardens and miniature
gardens. They serve as ground cover for Bonsai, as soil additives, in mulching
and root packing materials (Perin, 1962). Mosses such as Leucobryum
bowringii Mitt. and L. neilghem'ense C.Muell. are mixed with soil or sand for
cultivation of
Rhododendron shrubs. Rhytidoropsis robusta,
Thuidium
delicatulum Mitt. and Hypnum imponens Hedw. have been used for culture of
Orchids (Adderly, 1964; Perin, 1962). In nurseries, Campylopus sp. is found
being used extensively for air layering in Kerala as it maintains moisture for
several days (pers. obs.).
In the present study area, W.D. Theuerkauf of Narayana Gurukula at
Periya maintains a garden where the prime undergrowth is the bryophytes
introduced from different areas of South India. Mostly they maintain bryophytes
as beds for higher plants and as seed beds.
In Japan, Rhodobryum giganteum and Climaciumjaponicum are planted
for bowl cultivation and landscape trays since it looks very attractive (Ando,
1957). Majority of the species provide a substratum for the growth of higher
plants, hence in nurseries and in local gardens bryophytes are conserved
properly.
1.2.2. Medicinal uses
Since ancient times bryophytes have been in use by mankind, but most
of them were based on the 'doctrine of signature'. The liverwort, Marchantia
polymopha and Conocephalum conicum having the shape of cross section of
animal's liver, were used for curing liver diseases (Miller & Miller, 1979), for
treatment of jaundice and externally to reduce inflammation (Hu, 1987). Riccia
sp. was applied externally for the cure of ringworm disease as rosettes of Riccia
resemble to that of ring worm.
Mosses such as Sphagnum is known for the layman as a packing
material from the early days. It was found as a better absorbent than cotton in
addition to its antibiotic qualities and was frequently used for surgical dressing
by the people in armies (Schofield, 1969). The oil extract from the 'hair cap
moss' Polytrichum commune is used to beautify and strengthen the hair (Pant &
Tewari, 1990).
Glime and Saxena (1991) mentioned that Rhodobryum giganteum and
R. roseum have been used as crude drugs for the treatment of cardio-vascular
diseases and nervous prostration. Polytrichum commune reduces inflammation
and acts as antipyretic, laxative and hemolytic agent (Glime & Saxena, 1991;
Hu, 1987).
Pant et al. (1986) reported that burned moss ash mixed with fat and
honey in the form of ointment is used for cuts, burns and wounds by the people
of Himalayan region. Pant and Tewari (1989) also reported that people in
Pithoragarh of Uttaranchal district as well as in the villages of north-western
Himalayas use Marchantia polymorpha L. or M. palmata Nees as a medicine for
boils and abscesses.
Bryophytes display an interesting range of antibiotic activity. The
lipophylic extracts of several liverworts such as Bazzania, Frullania, Marchantia,
Plagiochila, Porella, Radula, etc. show antibacterial and antifungal activities
(Asakawa, 1990). Some of the bryophytes have also been detected as inhibitory
for carcinogenic growth (Belkin et al., 1952-53). He first tried alcoholic and
acidic extracts of Polytrichum juniperinum, on mice to test anticancer activity
against sarcoma and found that the results were promising.
The local people at Attappadi of Palakkad district, Kerala State call
mosses as 'kallupasa' and use a mixture of paste made from some leafy
liverworts such as Radula sp. and Spruceanthus semirepundus to cure burns
(Mr. M.Remesh, KFRI, pers.com.).
Although there is not much scientific evidence to support the
effectiveness of these treatments, however some successful experimental and
clinical evaluations are being carried out in China (Ding, 1982).
1.2.3. Pollution indicators
Bryophytes play a significant role as indicators of environmental pollution
and these plants can be employed in developing an Index of Atmospheric Purity
(IAP), because most of them have a sharply defined and rather narrow
ecological range. These plants have been successfully used to monitor air
borne pollution due to industrial emission. Nash (1972) in his studies on mosses
such as Ceratodon purpureus, Atrichum undulatum and Polytrichum piliferum,
revealed that Atrichum undulatum is one of the best bioindicator of air pollution.
Bryophytes have also been found to be useful as indicators of water
pollution. Bryophytes are excellent indicators of acid rain damage to ecosystem
(Nash & Nash, 1974) and they can also be used as indicators of climate change
and thereby study its effects on ecosystem (Gignac, 2001).
Mosses are the most frequently used plants for monitoring metal
pollutants in terrestrial habitats (Tyler, 1971). Some species such as Scapania
undulata, Fontinalis antipyretica, Jungermannia vulcanicola, etc. are quite
useful in monitoring heavy metal pollution. Certain species of bryophytes have
also been reported to grow on particular mineral deposits. Copper mosses such
as Mielichhoferia elongata, Scopelophila lingulata and S. cataractae prefer to
grow in very high concentrations of copper, sulphur and heavy metals
(Leimpriecht, 1895). Due to this property, bryophytes can be used as tools for
geological prospects (Pant, 1981).
1.2.4. Ecological importance
Many
species
of
bryophytes are
used
in land conservation.
Pleurocarpous mosses such as Hygrohypnum, Thuidium, Brachymenium, etc.
form a dense packing over stones and soil and preserve the microhabitat from
erosion. Important role of bryophytes in soil management is their quality to build
up rocks. Emig (1918) has observed the rock building in a stream where the
dense tufts of Didymon sp. are more commonly distributed along moist ledges
extending across the shallow streams. His observation explains that mosses act
indirectly in the precipitation of CaC03 mainly by providing a larger absorptive
and adsorptive surface for the evaporation of calcareous water. Some mosses
play an important role in slope formation (Marsh & Koerner, 1972). Barbula
unguiculata Hedw., Weissia controversa Hedw. and Bryum sp. are valuable in
erosion control (Conard, 1935).
In addition to these, bryophytes play an important role as pioneer plants
in occupying primary habitats as well as secondary habitats after disturbance.
They serve as homes for many invertebrates, and often provide construction
material for bird's nest. Pant and Tewari (1989) reported that in the remote
villages at district Almora on way to Pindari Glacier, mosses locally known as
'muk', are still utilized for making comfortable beddings and cushions by the
nomadic herdsmen.
1.3. PRESENT STATUS
Eventhough the Indian subcontinent is blessed with rich bryoflora, the
detailed documentation is but far from complete. This is mainly due to the lack
of infrastructure and resources. This group was gravely neglected, may be due
to the less direct economic potentials and associated glory. Eventhough the
studies in liverworts are done in some extent, we cannot claim to have thorough
knowledge of our moss wealth because many parts lie virgin or unexplored.
Regional exploration of such a large and diverse group of plants still remains
untouched.
More bryo-exploration is essential in unexplored areas otherwise many
species would perish and disappear before being documented from these
potential areas. Day by day the bryophyte luxuriance is dwindling, being
replaced by monstrosities or urbanization due to an increasing pressures of
population and other anthropogenic activities.
Moreover the lack of taxonomic literature is another major inadequacy in
the study of bryophytes. The difficulties are perhaps more acute in lndia
especially in South India, since there are no modern bryophyte floras. The
major work on Indian bryophytes is that of Gangulee's (1969-1980) Mosses of
Eastern lndia and adjacent areas, which is yet to be completed. Much of the
taxonomic literature is scattered and, for some groups, old and of limited value
in identifying specimens. Identification of bryophytes is therefore very difficult
eventhough there are good libraries and herbaria available, in northern part of
the state. Above all their small size and lack of trained specialist in this group
make the identification more difficult.
1.4. OBJECTIVESOF THE PRESENT INVESTIGATION
1. To generate baseline data on the bryophytes of Wayanad district by
undertaking a comprehensive field study with special reference to their
distribution pattern along altitudinal and vegetation gradients.
2. To provide details of distribution, description and key to identification.
3. To study the basic ecological aspects of bryophytes.
4. To collect information on the uses of bryophytes from the study area.
5. Understanding the problems of conservation and documentation of the rare
and threatened species in the study area.
1.5. RELEVANCE OF THE PRESENT INVESTIGATION
Bryophyte species tend to be highly specific with regard particular
microenvironment factors such as temperature, light and water availability,
substrate chemistry, etc. making them good ecological indicator species. Thus,
bryophytes are attracting much attention recently from applied ecologists and
conservation biologists. Despite this intrinsic interest and potential for scientific
study, a major limitation in the use of bryophytes as study materials for
evolutionary and ecological processes has been the lack of basic floristic and
alpha taxonomic knowledge of the plants in many regions, especially in the
tropics. The present work was undertaken with the objective of filling an
informational gap so that an overall bryofloral picture of a mountainous district
could be presented. Therefore, an attempt has been made to provide a record
of bryophyte species collected from diverse habitats of the Wayanad. And this
study also aims to present a model for the future eco-floristic studies on the
bryophytes for the entire State.