Transcript lycopodium - Govt College Ropar

INTRODUCTION
The modern representatives are small and
herbaceous sporophytes. The leaves are small
and simple. Each leaf possesses an
unbranched midrib. The leaves have no
ligules. There are no leaf gaps in the stele of
the stem. The sporophylls may or may not be
restricted to the terminal portion of branches
and organized into definite strobili. The
sporophylls and simple vegetative leaves may
be similar or dissimilar. They possess
homosporous sporangia, i.e., all the spores of
one kind only. The gametophytes are wholly or
partly subterranean. The antheridia remain
embedded in the tissue of the prothallus. The
antherozoids are biflagellate.
Classification
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Genus LYCOPODIUM:
Systematic Position:
Pteridophyta
Division. Lycophyta
Class.
Eligulopsida
Order.
Lycopodiales
Family.
Lycopodiaceae
Genus.
Lycopodium
There are about 180 species in this genus.
Distribution and habit:
• The species of Lycopodium are world-wide in distribution. They are
mainly found in tropical and sub-tropical forests. They are very
commonly found on heaths and on humus soils in moist shady
places. In India they are found in the hills of Eastern Himalayas.
• The plants are commonly known as ‘ground pines’, ‘club mosses’
and ‘trailing evergreens’ many species occur in the tropics as
hanging epiphytes (e.g., Lycopodium phlegmaria and L.
squarrosum). Chowdhury (1937) has reported eight species from
our country. These species are: Lycopodium clavatum; L. cernuum,
L. heamiltonii; L. setaceum; L. phlegmaria; L. wightianum; L.
serratum and L. phyllanthum. The most common species is L.
clavatum.
The Sporophyte
• Habit:
All species possess small, herbaceous or shrubby sporophytes. The
stem in almost all the species is delicate and weak. Some species
are epiphytic and with erect or pendant sporophytes while other
species are terrestrial and have a trailing habit. The stem and its
branches are densely covered with small leaves. Lycopodium
phlegmaria is an epiphytic species.
• According to Pritzel (1900) this genus is divided into two sub-genera
which differ from each other in general organization of the
sporophyte. These subgenera are-Urostachya and Rhopalostachya.
Stems
• Species referred to the sub-genus
Urostachya possess branched or
unbranched stems that are erect or pendant
but never creeping. This subgenus includes
the species, e.g., L. selago, L. lucidulum, L.
phlegmaria and others. If the stem is
branched, the branching is always
dichotomous. Usually the successive
dichotomies are found at right angles to one
another. The species belonging to this
subgenus do not bear the adventitious roots
along the stem.
Leaves
• The leaves are small, simple, sessile, numerous and cover
the axis closely. Typically the leaves are 2 to 10 mm long.
Usually the leaves are arranged in closed spirals (e.g., in L.
clavatum and L. annotinum) while in other cases they are
arranged in whorls (e.g., in L. verticillatum and L. cernuum).
• In some species the leaves are found to be arranged in
opposite pairs (e.g., L. alpimum); in others they are irregularly
arranged. Usually the leaves are lanceolate
• In some species the leaves are found to be arranged in
opposite pairs (e.g., L. alpimum); in others they are irregularly
arranged. Usually the leaves are lanceolate
Apical growth
• The apical growth of the shoot
takes place by means of an
apical meristem which consists
of a group of apical cells.
Roots
• The first root is short and at least in some species does not live long.
The older plant bears the adventitious roots that arise singly or in
groups acropetally along the lower side of the stem. The species of
subgenus Urostachya do not possess adventitious roots along the
stem. The species of the subgenus Rhopalostachya with a creeping
stem generally have their adventitious roots borne along the entire
length of the prostrate portion.
• In some species, e.g., L. selago, L. phlegmaria and others the roots
that arise on the outside of the stele do not penetrate the cortical
region of the stem at once. These roots turn downward and
penetrate the soft middle cortex making canals through it, and
ultimately they emerge only at the stem. Such roots are known as
‘cortical roots’ or ‘inner roots’.
• In some species, (e.g., L. obscurum and L. lucidulum) the branching
of the roots is strikingly dichotomous. Here each successive forking
is found at right angles to the preceding one. In many species the
dichotomy is obscure. The endogenous lateral roots do not arise
from the roots (as in seed plants). In terrestrial form the root hairs
are found abundantly which persist over a long period.
Anatomy of the stem
• A transverse section of the mature
stem of Lycopodium clavatum shows
the following structures:
• The epidermis is one cell in thickness
and has stomata that appear to be
similar in structure to those of the leaf.
The outer walls of the epidermal cells
are thick and cutinized.
• The cortex is quite broad and it varies
greatly in relative thickness from
species to species. In some species
its radial thickness is several times
that of the stele; in other species the
two are approximately equal. The
cortex has three zones. The peripheral
and central zones consist of thickened
sclerotic cells while the middle zone
consists of larger and thin-walled cells
containing a few chloroplasts.
ENDODERMIS
• The single stele occupies about half the
area of the section. It consists of a number
of irregularly shaped, parallel strands of
xylem alternating with phloem bands. The
xylem consists
• Mainly of scalariform tracheids, with no
vessels and no parenchymatous cells.
Each Xylem plate remains surrounded by
a single layer of parenchyma, with
bordered pits on the inner walls, which lies
between the xylem and the phloem.
• The phloem is composed of sieve tubes
and parenchyma only. The development of
both xylem and phloem strands is
centripetal, that is, from the periphery
towards the cente.
.
• The protoxylem consists of spiral and annular
tracheids. The protoxylem is found to be situated at
the outer edges of each xylem mass, that is to say, in
the exarch position.
• At the inner face of the cortex there may be an
endodermal layer which, at least in younger portions of
the stem has characteristic thickened radial walls.
• The endodermis of Lycopodium is thought to be
originated from the stele and not from the cortex.
Internal to the endodermis there lies a multilayered
pericycle. The pericycle layer is usually three to six cell
in thickness
.
• There is a great variation of organization of
the vascular elements, not only in different
species but even within the same species
may vary both from individual to individual
and in different portions of the same
individual. In stems the vascular elements are
found to be arranged into an exarch
actinostele resembling to the actinosteles
characteristic of roots of vascular plants.
• In such steles the phloem lies in the space
between the xylem plates. For example, in L.
phlegmaria, the adult stem has the exarch
actinostelic organization with rays of varying
number. In L. serratum the xylem rays are
expanded outwards like fan blades in
appearance.
.
• According to J.B. Hill (1914), the species with actinostelic type
of organization in the older portions of the stem are thought to
be the most primitive of the genus as far as the vascular
organization is concerned. Other species may have
plectostelic organization of the vascular elements. In such
stems the xylem core is found in the form of plate like lobes.
• Here the xylem and phloem bands are found to be arranged
symmetrically in alternating transverse bands across the stele
(e.g., in L. volubile and L. wightianum). In still other species
the stelic organization may have masses of xylem and phloem
indiscriminately mixed with one another, e.g., in L. cernuum.
• Holloway (1910), Jones (1905) hold the view that the
plectostelic organization is found chiefly in horizontal portions
of the plant and the actinostelic in erect portions. The stele
lacks a cambium in all cases and hence there is no secondary
growth.
Anatomy of leaf
• The transverse section of leaf shows
following parts.
• The leaf has a mid-rib which consists
of a single concentric amphicribral
bundle. The central xylem core is
quite small. It is not always
differentiated into Meta-and
protoxylem. The xylem is composed
of thick walled annular and spiral
tracheids. The phloem is composed
of phloem parenchyma and narrow
sieve-tubes. The endodermis is
inconspicuous and may hardly be
recognized. The vascular bundle
remains surrounded by
sclerenchymatous pericycle.
Anatomy of root
• The transverse section of the root
shows the following parts:
• The root is differentiated into
epidermis, cortex and stele like other
vascular plants. The single layered
epidermis gives rise to numerous
root hairs. The root hairs are formed
to be arranged in pairs. According to
Stokey (1907), the occurrence of root
hairs in pairs results from the fact
that the hair initials are found in twos
by the oblique or anticlinal division of
a young epidermal cell.
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• Just beneath the epidermis there lies the broad cortex. The cortex is
several cells in thickness and often becomes greatly sclerified in the
outer half as the root becomes older.
• In some cases the stele is monarch with the protoxylem in one
mass, e.g., in L. clavatum. In other cases the stele is diarch with two
protoxylem masses, e.g., in L. selago, L. reflexum and other
species. Here the two xylem masses are united into one continuous
xylem group which is C-shaped or horseshoe shaped.
• In still other cases the stele is triarch with three groups of
protoxylem. According to Saxelby (1908), sometimes the same root
is diarch in one portion and tetrarch in another (e.g., in L. selago and
others). Most roots are diarch. These roots generally have but one
mass of phloem and this lies between the protoxylem points of
the C or U shaped xylem.
The spore bearing organs
• In most species of the subgenus Urostachya, the foliage
leaves and sporophylls are approximately of the same size
and both are green. However, there is variation in the
distribution of foliage leaves and sporophylls. In Lycopodium
selago and many other species there are alternate sterile and
fertile regions throughout length of stem and branches. These
portions of the plant are called strobili.
• The strobili of different species are varied from each other.
The strobili of L. phlegmaria and other related species are
dichotomously branched and here the sporophylls, although
green and of the same shape are comparatively much smaller
than the foliage leaves.
• All species of the subgenus Rhopalostachya have the
sporophylls in well defined strobili which may be simple or
branched. The sporophylls may be differentiated from foliage
leaves in that they are smaller in size, paler in colour and
have a dentate margin.
Vegetative propagation of the sporophyte
• The vegetative propagation is
frequently found in the species of
Lycopodium. Several methods of
vegetative propagation are found in
different species of Lycopodium. The
species possessing creeping stems
have the apical growth branching
and the progressive death of the
older portions.
• According to Holloway (1917) the
new plants may be developed from
(a) vegetative propagation of the
gametophyte, (b) vegetative
propagation of the juvenile stage of
the sporophyte, (c) gemmae
produced from the cortical cells of
the root, (d) tubers developed at the
apices of roots and (e) bulbils. All
above mentioned vegetative bodies
are capable to develop into new plants.
.
• The bulbils which are found only in species belonging to
subgenus Urostachya resemble superficially to the
protocormous stage (juvenile stage) of young
sporophytes. The bulbils may develop anywhere on the
stems. According to R.W. Smith (1920), these bulbils are
interpreted as modified leaves while other workers
interpret them as modified lateral branches or modified
sporangia.
• A sporophyll produces but one sporangium. The
sporangium remains adaxial in its position and found
near the base of the sporophyll. A mature sporangium is
always kidney-shaped. Each sporangium possesses a
long and slender or short massive stalk, according to
species.
Development of sporangium
• The sporangia begin to develop at a
time when the sporophyll is
composed of embryonic cells. First of
all there is a periclinal division of a
small group of epidermal cells on the
adaxial side of a sporophyll and near
its base
• The inner daughter cells formed by
this periclinal division give rise to the
stalk and the basal portion of a
sporangium. The outer daughter
cells contribute to the formation to
the bulk of the sporangium. The
outer cells again divide periclinally
forming an outer layer, the jacket
initials; and an inner layer, the
archesporial cells.
• The archesporial cells divide periclinally and anticlinally forming a
massive sporogenous tissue. The cells of the last generation of the
sporogenous tissue act as spore mother cells. They become
rounded and are being separated from one another. Now these
spore mother cells float about in a viscous liquid and divide
meiotically into tetrads of spores.
• The jacket initials, which are found external to the sporogenous
tissue divide repeatedly forming a jacket layer of three or more cells,
in thickness. Shortly before the development of the spore mother
cells a nutritive tapetal layer is formed around the sporogenous
tissue.
• This layer is partly formed from the inner-most layer of jacket cells
and partly from sporangial cells found just beneath the sporogenous
tissue. As found in most other pteridophytes, in Lycopodium there is
no disintegration of the Tapetum during spore formation.
Dehiscence of sporangium
• The mature sporangium is about 2 mm
across and kidney-shaped. On the
maturity of the sporangium narrow
transverse strip of cells, the stomium is
formed across the apical portion of the
outermost jacket layer.
• The cell walls of the stomial portion
become thickened and may easily be
differentiated from those of other cells
present in the jacket layer of the
sporangium. The mature sporangium
ruptures by a transverse slit at its apex
along the line of the stomium. The
sporangium divides into two valves
which remain united at the base and
dehiscing the yellow spores.
The Gametophyte
• The spore:
• The small spores (about .03 to .05 mm. diameter) are uniform in size
and shape, i.e., homosporous. This way Lycopodium is similar to
most of the ferns and Equisetum. The spores are round or
tetrahedral in shape. They are very light possessing thin exine
formed of concentric lamellae, and a granular intine.
1. Netzsporen
This type of spores possess an outer wall with reticulate ridges
(e.g., in L. clavatum, L. complanatum and L. annotinum). 2.
Tupfelsporen. This type of spores possess knoblike outgrowths
from the surface (e.g., in L. selago and L. phlegmaria). 3. This is a
transitional type possessing a fine ridged pattern (e.g., in L.
cernuum and L. inundatum).
Germination of spore and
development of prothallus
• The spores settle on the ground after their
liberation from the sporangium and each
germinates into a prothallus. Sometimes the
germination of spore may, however, be
delayed for years. According to Treub (1888),
the spores germinate within a few days after
they are shed (e.g., in L. cernuum, L.
inundatum and L. salakense).
• In L. clavatum the spore germination begins
after three to eight years of their shedding.
Here the prothallus is a subterranean
structure, solid and tuberous which takes from
six to fifteen years to mature. The prothallus
of L. clavatum is colourless and saprophytic
and contains a mycorrhizal fungus.
Development of archegonium
• The archegonium
develops from a single
superficial cell of
prothallus found just
back of the apical
meristem. This cell is
known as archegonial
initial. The arcehegonial
initial divides periclinally
into a primary cover cell
and central cell
• According to Bruchmann (1910), the first
cell division of a germinating spore takes
place before the outer spore wall (exine) is
ruptured and results in two hemispherical
daughter cells of approximately equal size.
The lower or inner daughter cell also
known as basal cell cuts off a small lens
shaped rudimentary rhizoidal cell while the
outer daughter cell divides twice
successively producing an apical cell with
two cutting faces.
• In the species with subterranean colourless
prothalli a long period of rest, about one
year is required between the five-celled
stage and the mature prothallus. Upto four
to five celled stage the early growth of the
prothallus takes its nourishment from the
reserve material contained in the mature
spores.
• Thereafter 4-6 celled gametophytes may have an entrance of
a symbiotic phycomycetous fungus into the basal cell. If there
is no entrance of the fungus there is not further development
of the gametophyte. After the establishment of the endophytic
mycorrhiza within the cells of the young prothallus, the apical
cell cuts of some half dozen segments and then becoming
replaced by a group of meristematic cells.
• The segments thus cut off by the apical cell divide periclinally,
and the outer cells thus formed become infected with the
symbiotic fungus in the same way as does the basal cell. The
apical group of meristematic cells, which are formed early in
the development of a gametophyte produces the major
portion of the adult prothallus.
• There is great diversity in form and structure of mature
gametophytes in the different species of Lycopodium. There
are three main types of mature prothalli. They are as follows:
• The first type of prothallus is mainly found in L. cernuum, L.
obscurum and L. inundatum. Here the prothallus is
inconspicuous and reaches to the maximum height of 2 to 3
mm and usually 1 to 2 mm in diameter. The prothallus grows
on the surface of the ground. It is an upright fleshy structure
whose lower portion remains embedded in the soil.
• On its upper exposed part the prothallus bears green lobes
with meristematic plates. The sex organs are found between
the green expanded lobes. The prothallus can manufacture its
own food, though an endophytic roycorrhiza is always
present. Rhizoids are also produced from the prothallus.
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• The second type of prothallus
is found in the species, e.g., L.
clavatum, L. complanatum, L.
obscurum and L. annotinum.
The prothalli are of various
shades. They are brownish
yellowish or colourless. They
are saprophytic and found
underground at various depths
from one to eight centimeters.
Much food material remains
deposited in these tuberous
prothalli.
• .
• In L. clavatum the prothallus is much convoluted structure 1 to 2 cm.
long with a pointed basal part. The surface is covered with an
epidermis. Inside the epidermal layer there is a cortex of several
layers. Just beneath the cortex there lies a palisade tissue
composed of a single layer of elongated cells. These outer layers
contain the endophytic fungus. This region is followed by a central
tissue of hexagonal cells which store up food material. Long
unicellular rhizoids are formed on the under surface of the
prothallus.
• The sex organs are borne on the top surface of the prothallus. It is
called the generative tissue. The cells of this tissue do not contain
any food reserves and they remain meristematic for some time. The
antheridia develop in the central portion and the archegonia towards
the rim. The antheridia develop first and the archegonia appear later.
The development is centripetal
• The third type of prothallus is
found in L phlegmaria and
other epiphytic species.
These saprophytic
colourless prothalli develop
beneath the surface of the
humus found on the tree
trunks. The prothallus
consists of an irregularly
shaped tuberous body from
which colourless, cylindrical
branches are given out. The
sex organs are borne on the
upper surface of the
enlarged branches. These
branches of the prothallus
are interspersed with slender
paraphyses.
Nutrition of prothallus
• The mode of nutrition of the
prothallus is remarkable. The cells
of the cortical region and the
palisade tissue remain filled with
endophytic fungus, and these form
a mycorrhizal association with the
cells of the prothallus. This
association is supposed to be
symbiotic. The entry of the fungus
takes place shortly after the
germination of the spore, and if it
does not take place the
gametophyte never develops
more than five cells.
Development of antheridium
•
•
The antheridium develops from a superficial
cell of prothallus found to be situated just
back of the apical meristem. The antheridial
initial divides periclinally into an outer cell,
the jacket initial and an inner cell, the
primary androgonial initial. The primary
androgonial cell divides repeatedly forming a
large mass of androgonial cells that lie
embedded within the prothallus.
Simultaneously the jacket initial divides and
redivides anticlinally forming a jacket layer
around the mass of androgonial cells, one
cell in thickness. The jacket layer in L.
phlegmaria is two layered towards the
periphery. The androgonial cells of the last
division being antherozoid mother cells or
androcytes. Each androcyte metamorphoses
into an antherozoid.
.
• The mature antheridium consists of an
oval mass of antherozoid mother cells
that projects out slightly from the
prothallial tissue and surrounded by a
wall, which is partly formed by the
jacket layer and partly from prothallial
cells.
• The antherozoids are fusiform, broadly
rounded at the posterior end with two
flagella at the anterior end. The
antherozoids closely resemble those
of the Bryophyta. This suggests the
closer linkage of Lycopodiales with the
mosses than with the ferns.
• Liberation of antherozoids takes place
by a breaking down of the opercular
cell in antheridium.
Development of archegonium:
• The archegonium develops from a single
superficial cell of prothallus found just back of
the apical meristem. This cell is known as
archegonial initial. The arcehegonial initial
divides periclinally into a primary cover cell
and central cell
• (Lang, 1899; Bruchmann, 1910; Spessard,
1922). The primary cover cell divides
anticlinally forming four neck initials, which
undergo transverse division to form a long and
straight neck, 3 to 4 cells in height and
composed of four vertical rows of cells. The
central cells divides periclinally into a primary
canal cell and a primary venter cell. The
former cell gives rise to about six neck canal
cells, while the latter functions directly as egg
or it divide to form a venter canal cell and an
egg.
• The portion of the mature archegonium
derived from the primary cover cell,
together with the neck canal cells it
ensheaths, projects vertically above the
prothallus. The remaining canal cells and
the oosphere (egg) lie embedded within
the prothallus. The cells lateral to the egg
and lower portion of the row of neck canal
cells are not portions of the archegonium
as they are formed by division and
redivision of prothallial cells immediately
adjacent to the archegonial initial.
• As found in the archegonia of bryophytes,
all cells of the axial row except the egg
disintegrate prior to the maturation of
archegonium, the apex of the neck of the
archegonium opens by the spreading
apart and partial disintegration of the
uppermost neck cells.
• The antherozoids make their way down
the neck of the archegonium and one
fuses with the oosphere thus effecting the
fertilization. The oospore (2n) is formed.
.
• The cells of this octant are arranged in two superimposed
tiers of four cells each. The tier of cells adjacent the
suspensor develops into the foot of the young sporophyte.
The foot remains as an intraprothallial Haustorium which
derives food from the prothallus until the embryo at length
becomes independent. The distal tier of cells develops into
the remaining portions of the sporophyte, viz., stem, leaf and
root.
• According to Bruchmann (1910), the two cells facing the
apical meristem of the prothallus develop into the stem and
the two cells facing away from the meristem develop into the
cotyledon and the primary root. The young sporophyte
becomes many celled structure prior to the differentiation of
• the cotyledon and the embryonic stem.
• The primary root
becomes evident even
later and at one side of
the region where
cotyledon and foot
adjoin each other. Until
this time the embryo
remains embedded
within the prothallus
and grows downward
and forward toward the
meristem of the
prothallus. Thereafter
the growing stem and
cotyledon burst through
the apical region of the
gametophyte. Now the
cotyledon and the stem
start to grow upward
into the air.
Development of embryo
• According to Bruchmann (1910) the
first division of a zygote is always
transverse and separates an upper
cell, the suspensor which does not
divide again. The lower cell also
known as embryonic cell divides
thrice. The first division of embryonic
cell is vertical and this is followed by a
vertical division of two daughter cells
thus formed. Transverse division of
each of these cells results in an eightcelled embryo.
Morphology of protocorm
• In certain cases the distal four cells of the
octant-stage form a massive spherical
structure, the protocorm. The protocorm
becomes green and develops through the
prothallus. The rhizoids develop on the
lower surface of the protocorm, the upper
surface of the protocorm gives rise a few
to many erect, conical outgrowths known
as protophylls. These structures are leaflike in function and bear stomata in their
epidermal layer. After the formation of
many protophylls, the protocorm is then
differentiated a meristematic region which
develops into the stem of the adult plant.
Economic importance of lycopodium
• The plants of lycopodium are beautiful & are therefore used for
decorative purposes. L.obscurum also known as “ christmas greens”
, is used in Christmas wreaths & other decorations. L.volubile is
used for table decorations.
• Dust like spores of Lycopodium clavatum are used in pharmacy as
water repelent & protective dusting powder for soft & tender skin.
• The spores of L.inundatum yield a high amount of fixed oil, which
are used as cover for pills.
• Plants of Lycopodium have medicinal value. Their extracts are used
as kidney stimulant. It is also used in homeopathic system of
medicine as name Lycopodium.
• The spores of Lycopodium are highly inflammable & used in flares,
fireworks & stage lightening.
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