Systematic Position of Lycopodium
Kingdom- Plantae (Plants)
Sub-Kingdom- Trachaeobionta (Vascular plants)
Division- Lycopodiopsida (Lycopods)
Order- Lycopodiales
Family- Lycopodiaceae
Genus- Lycopodium
Sub-Genus
a) Urostachya– In this type, the branching dichotomous and roots originates from the base of the stem. E.g. Lycopodium selago.
b) Rhophalostachya– In this type, the stem prostrate with erect branching and roots originates adventitiously along the entire stem. E.g. L. inundatum.
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Occurrence and Habit of Lycopodium
Lycopodium is a cosmopolitan genus with about 400 species that are found under varied habitats. Lycopodium are commonly found in tropical, sub-tropical and temperate region but some of the species are also found in colder climatic region.
Most of the tropical species are epiphytic and grow hanging from the tree trunks. The temperate species grows in open wood-lands and on moist and acidic soils. Species like L. squarossum, L. linifolium are epiphytic whereas species like L. annonitum, L. cernum are terrestrial.
Morphology of Lycopodium
The stem of Lycopodium is either erect or prostrate and is dichotomously branched. The two branches formed as a result of dichotomy may grow equally or unequally in different species. The tip of the branches bears strobili.
The leaves are simple, sessile, and small in size and possess a single mid-vein. These leaves are called microphylls. The leaf margin may be entire or serrate and the leaves lack ligule. These leaves are either decussate or whorled or spirally arranged. The leaves may be isophyllous or anisiophyllous.
The roots are dichotomously branched, adventitious and arise endogenously from the lower side of the prostrate stems in an acropteal order.
In the erect stems, the roots come out form the basal part of the stem.
Growth of Lycopodium
The growth of the shoot takes place by means of an apical meristem which consists of group of apical cells. The derivatives of these cells differentiates into primary meristematic tissue; the protoderm, the ground meristem and the procambium. The protoderm gives rise to epidermis, the ground meristem gives rise to cortex, endodermis, pericycle and the pith. The procambium gives rise to vascular tissue.
Anatomy of Lycopodium
The transverse section of Lycopodium stem reveals
Epidermis
It is a single layer of parenchymatous cells with cutinised outer walls and stomata.
Cortex
It is present next to the epidermis and varies from species to species. In some cases, the cortex is made up of thin walled with intercellular spaces. This type of cortex is called homogenous cortex.
In some cases, the cortex is made up of sclerenchymatous cells without the intercellular spaces.
In other cases, the cortex is divided into three zones i.e. the hypodermis, the middle zone and the inner zone. This type of cortex is called heterogenous cortex. Hypodermis is made up of thick-walled cells, the middle zone is made up of thin-walled cells with lots of intercellular spaces and the inner zone is made up of thick-walled cells.
The last layer of cortical cells is called endodermis. Endodermis contains casparian strips.
Pericycle
It is present next to the endodermis and composed of one or many layers compactly arranged parenchymatous cells.
Stele
Different types of stele can be seen in different species of Lycopodium. In L. selago, L. serratum, the type of stele found is actinostele in which the xylem appears star-shaped with protoxylem situated at the tip of the star shaped projections and is exarch.
In species like L. volubile, the type of stele found is plectostele in which the xylem appears to be in the form of separate plates.
In species like L. cernum, mixed protostele is present in which the xylem and phloem are distributed uniformly. It appears like the strands of xylem are embedded in the phloem.
In species having stems with larger diameter, e.g. L. densum the type of stele present is plectostelic protostele.
Strands of the vascular tissue called the leaf traces extend outwards from the stele runs obliquely towards the cortex. Only a single strand enters the leaf to form single median vein. Similarly stele is connected to each branch by a branch trace. There are no leaf gaps.
The anatomy of Lycopodium leaf reveals
Epidermis
It is a single layer of compactly arranged cells covered by a layer of cuticle. It is perforated by stomata. The stomata may be on both the sides of the leaf in isophyllous species and only on lower epidermis in some anisophyllous species.
Mesophyll
It is undifferentiated and consists of loosely arranged chlorophyll cells with small or large intercellular spaces.
Vascular region
A single un-branched vascular strands traverses the leaf. The vascular bundle is mesarch. There is no clear distinction between protoxylem and metaxylem.
The anatomy of Lycopodium root reveals
Epidermis
It consists of single layer of thin-walled cells and is covered by numerous root hairs. The root hairs are arranged in pairs.
Cortex
The cortex is divided into two distinct regions- The outer cortex and inner cortex. The outer cortex is composed of several layers of thick-walled cells. The inner cortex is parenchymatous. Endodermis and pericycle is not distinguishable.
Stele
The stele may be diarch, tetrarch or polyarch. In most of the creeping species, the type of stele is polyarch. There is no pith and the stele consists of xylem plates arranged in a radial fashion. In most of the erect species, the type of stele is diarch or tetrarch.
Reproduction of Lycopodium
Vegetative propagation
Lycopodium reproduces by following methods-
- By the formation of gemmae or bulbils- These are modified vegetative structures that arise as lateral out-growths from near the stem apices and take the place of leaves. Each bulbil consists of a short reduced axis surrounded by a number of thick fleshy leaves. These leaves store food material. These remain on the plant till root primordial appear on the shortened stem. The gemmae fall on the ground and grow into a young plant. This type of reproduction occurs in L. segalo, L. lucidulum etc.
- Fragmentation- Death and decay of older regions of the stem leading to the separation of younger branches which grow into separate plants is also a common method of vegetative propagation in Lycopodium.
- Formation of Resting Buds- In L. inundatum, the tips on the apical buds of rhizome and its branches store food material and become surrounded by densely crowded leaves. These are the resting buds. Under unfavourable condition, the rest of the plant except these buds dies. At the advent of favourable conditions, the resting buds resume growth and give rise to new plants.
- Formation of Root Tubercles- In L. ramulosum, tubercles originate from the parenchymatous region of the root cortex. They consist of a group of cells with stored food material and protected by thick walls and have the capacity to germinate into new plants.
- Formation of adventitious buds- The epidermal cells of the leaves proliferate near the base and grow into buds. In some cases, decapitation of stem near its apex and modification of leaf rudiments also leads to the formation of buds. These buds later give rise to new individuals. Example L. selago and L. inundatum.
Sexual reproduction in Lycopodium
Formation of spores
The sporophyte produces sporangia, which are specialized structures where spores are formed by meiosis.
Strobilus
The leaves near the apices or branches bear sporangia and are known as sporophylls. The aggregation of sporophylls is called strobilus. The arrangement of sporophylls may be loose when they form loose strobilus or maybe arranged compactly to form definite strobilus. In Urostachya, every leaves or alternate leaves on the plant is a sporophyll. In Rhophalostachya, the leaves of the apical portion bear sporangia and are called sporophylls.
Sporangium
The sporangium is mostly reniform or kidney shaped and sometimes sub-spherical. It is usually raised on a short massive stalk. The stalk is indistinct in some species. The sporangia arise singly and maybe sub-foliar and exposed as in case of L. squarossum, foliar and protected as in case of L. cernum, protected as in case of L.inundatum or axillary and exposed as in case of L. lucidulum.
Structure of sporangium
The sporangium consists of two parts- the stalk and the capsule. The stalk may be short and distinct in some species like L. phlegmaria or indistinguishable in species like L. cernum. The stalk bears a curved and reniform capsule which is not lobed and is unilocular. It has a three or more layered wall surrounding a mass of spore mother cells. The innermost layer is the tapetum and the cells of this layer have larger nuclei, granular cytoplasm and nutritive substances. The sporogenous tissue forms spore mother cells which undergoes meiosis to form spores.
Development of sporangium
The sporangium originates from a single transverse row of superficial cells on the dorsal or upper surface of the chlorophyll near its base or close to its point of attachment with the stem.
- Each of these cells divides to form middle row of archesporial cells surrounded by a row primary wall cells above and below.
- The upper cells contribute to the formation of sporangial wall, the stalk and the tapetum.
- The lower cells contribute to the tapetum in the lower basal part of the sporangium. These lower cells as it appears in median radial section or appear in a tangential section constitute the sub-archesporial cells.
- In the species belonging to Rhophalostachya e.g. L. clavatum, there is more than one row of archesporial cells.
- The primary wall cells undergo periclinal and anticlinal divisions to form a three or more layered thick sporangial wall. The innermost layer is differentiated as tapetum. This layer provides nutrition to the developing sporangia.
- The tapetum in the basal region of the sporangium differentiates from the subarchesporial cells. In some species the tapetum layer does not undergo disorganization to form the periplasmodial fluid.
- The archesporial cells divides mitotically in various planes to form a group of cells called the sporogenous tissue. These cells grow in size and separates to form spore mother cells or sporocytes. The sporocytes undergo meiosis and produce tetrahedral haploid spore tetrads.
Dehiscence of sporangium
When the sporangium reaches maturity, the transverse row of cells is differentiated near the apical portion and is known as stomium. The inner walls of the cells constituting the stomium are thick and lignified. The cells of sporangium other than the stomium have their side walls thickened only. As the exposed sporangia lose water and dry, a condition of stress develops which leads to the formation of slit in the stomium and cause the sporangial wall to open from top to the base. The spore mass projects out of the open slit and disseminates.
Structure of spore
Lycopodium is homosporous. The spores occur in tetrads having a tetrahedral shape with a rounded or semi-circular base. Each spore has a triradiate ridge and is enclosed within a thin or thick spore wall. The spore wall has two layers. Each spore has a single haploid nucleus surrounded by cytoplasm. The chloroplast may or may not be present.
Gametophyte
It starts with the spore that germinates to give rise to a new individual called the gametophyte or the prothallus which is formed by germination of spores.
Germination of spore
The spores germinate under moist conditions. They absorb water and swell up. The cytoplasm and nucleus divides mitotically to form two unequal cells.
The larger cell takes part in the formation of prothallus and the smaller cell called rhizoidal cell and does not takes part in prothallus formation.
The spore wall ruptures along the tri-radiate mark and the two-celled prothallus projects out.
The larger cell then divides to form basal cell and upper cell. The young prothallus is at three celled stage i.e. the rhizoidal cell, the basal cell and the upper cell. The third cell further undergoes two successive divisions. This is the five-celled stage of young prothallus.
In those species producing aerial prothalli, the rest of the stages leading to the formation of mature prothalli depend upon the attack of mycorrhizal fungus.
In those species producing subterranean prothalli, the resting period intervenes between further developments. During this stage, mycorrhizal infection takes place. Further growth is resumed and is marked by the activity of apical cells which is later replaced by meristematic cells and divides repeatedly to form mature prothallus.
Types of mature prothallus
First type
This type of prothallus has an erect cylindrical body. It grows at the surface of the ground and consists of a colourless basal portion and aerial crown that is green in colour and bears sex organs at the base of green lobes. The rhizoids are present at the lower buried portions and also contain endophytic fungus. The portion of prothallus bearing the sex organs are called generative zone. This type of prothallus is seen in species like L. cernum, L. inundatum.
Second type
This type includes subterranean prothalli that have acquired saprophytic mode of nutrition. The prothalli are yellowish brown or colourless and store sufficient food material. Their shape varies from conical, top-shaped or discoid.
They have two distinct regions- the upper broad generative region and the lower conical region. The generative region contains sex organs i.e. the antheridia and archegonia being located at the centre and near the margins respectively.
The conical region shows distinct zones: the outermost layer representing epidermal tissue and bears rhizoids.
Next to this lies the cortical zone composed of parenchymatous cells.
Next to this is palisade zone made up of columnar cells that contains hyphae.
Next to this is the storage zone consists of cells with reserved food material.
This type of prothallus is found in species like L. clavatum, L. obscurum etc.
Third type
This type includes colourless, subterranean, saprophytic and repeatedly branched monopodial prothalli that are found in the epiphytic species of Lycopodium. The growth of the prothallus and its branches is apical and takes place by the activity of two prismatic initial cells that lie side by side. In this case, the endophytic fungus is found in the inner core of cells. This centrally located mycorrhizal region is surrounded by one or more layers of cortical cells that are devoid of endophytic fungus and are colourless. The rhizoids arise from the outermost layer. The prothallus reproduces vegetatively by fragmentation and gemmae formation. The generative zone bear sex organs with paraphyses. This type of prothallus is present in L. phlegmaria.
Sex organs of Lycopodium
The exosporic gametophytes of Lycopodium are essentially monoecious but protrandus. The antheridia and archegonia in most of the species are formed in distinct patches or clusters on the upper surface of the prothallus.
Antheridia in Lycopodium
The antheridia develop earlier than archegonia and are mostly embedded in the tissue of prothallus.
Development– The antheridium arises from a single superficial cell which divides by a transverse wall into an outer primary wall cell and inner primary spermatogenous cell.
The primary wall cell divides by anticlinal wall to form the jacket of the antheridium. The triangular opercular cell is differentiated in the middle of the jacket cell and marks the point of exit of spermatozoids.
The primary spermatogenous cell divides repeatedly to give rise to a mass of androgonial cells. The androgonial cells divides further and give rise to mass of spermatocytes or sperm mother cells which give rise to spermatozoids.
Structure of antheridium– A mature antheridium is either completely embedded in the tissue of prothallus or slightly projecting. It has a single-layered antheridial wall (jacket) with opercular cell. This wall encloses large number of oval, biflagellate spermatozoids. It dehisces by the formation of mucilage from the opercular cell and rupturing of antheridial wall due to the absorption of water by the spermatozoids.
Archegonia in Lycopodium
It develops after the development of antheridia.
Development- The archegonium arises from single superficial cell which divides periclinally to form outer primary cover cell and inner central cell.
The primary cover cell divides by two intersecting walls into four neck initials which divide further by transverse walls to give rise to the neck that varies from three to many cells in height. The neck is composed of four longitudinal rows.
The central cell divides by a transverse wall into an upper primary canal cell and a lower primary ventral cell.
The primary canal cell gives rise to neck canal cells and the number varies from species to species. The primary ventral cell undergoes a transverse division from a lower egg cell and an upper ventral canal cell. In some cases, the primary ventral cell functions as the egg cell.
Structure- A mature archegonium consists of a venter and an egg. The length of the neck varies from species to species. The neck encloses a neck canal which contains 1-16 neck canal cells. The venter contains ventral canal cell and egg cell and does not contains its own protective layer of cells rather it is protected by the tissue of prothallus.
Dehiscence- The archegonium dehisces by the disorganization of the neck canal cells and the ventral canal cells which creates an open passage for the spermatozoids to enter the neck and reach the egg.
Fertilization in Lycopodium
It occurs in the presence of water. The spermatozoids swim and reach the open archegonial neck. The archegonial neck secretes some chemicals due to which spermatozoids are attracted towards it. Only one spermatozoid is able to reach the egg and fertilization takes place and zygote is formed.
Embryo
The embryo is endoscopic i.e. the shoot apex is directed away from archegonial neck. The nucleus of oospore divides to form hypobasal and epibasal cell. The cell next to archegonial neck is epibasal and the cell away from it is hypobasal. The epibasal cell forms the suspensor. The hypobasal cell divides and re-divides to two quadrants. The hypobasal quadrant that lies next to the suspensor give rise to foot and another quadrant form the shoot and primary root. Further growth of the embryo takes place away from the archegonial neck. The development and differentiation of various parts such as leaves, roots etc. varies from species to species.
Economic Importance of Lycopodium
- The spores of Lycopodium are used as a reducing agent in gunpowder.
- Lycopodium are also been traditionally used in homeopathy and herbal medicine. They are believed to have diuretic, laxative, and tonic properties.
- Some species like Lycopodium clavatum are used for treating digestive disorders, stomach aches, and diarrhea.
- Lycopodium spores are also used as a powder for coating pills due to their non-reactive and fine texture and are also used as a dry powder in various industries, including as a dusting powder in the glove manufacturing industry and as a separating agent in metallurgy.
- Due to their fine and non-sticky nature, Lycopodium spores are utilized as a dry lubricant.
- Lycopodium species are popular in horticulture for their unique appearance and are used as ornamental plants in gardens and also used on various ceremonial occasions.
References
- R, V. (2016, September 16). Lycopodium: Habit and habitat and morphology. Biology Discussion. https://www.biologydiscussion.com/pteridophytes/lycopodium-habit-and-habitat-and-morphology/53176
- Libretexts. (2022, May 4). 6.1.1: Lycopodium. Biology LibreTexts. https://bio.libretexts.org/Bookshelves/Botany/A_Photographic_Atlas_for_Botany_(Morrow)/06%3A_Seedless_Vascular_Plants/6.01%3A_Lycophytes/6.1.01%3A_Lycopodium
- S, S. (2014, February 22). Lycopodium: Useful notes on lycopodium. Your Article Library. https://www.yourarticlelibrary.com/biology/lycopodium-useful-notes-on-lycopodium/7432
- Pteridophyta by B.R. Vashishta, A.K. Sinha, Adarsh Kumar (S.Chand & Company ltd)
- Hait, G., Bhattacharya, K., & Ghosh, A. K. (2012). A textbook of Botany, Volume I.
- Bhamble, S. (1965a). Ibid. 61 ; 242-252 (Lycopodium)
- Rashid, A. (1999). An Introduction to Pteridophyta : Diversity Development. Differentiation. Vikas Publishing House Pvt. Ltd. New Delhi.
- USDA Forest Service. (2006). Fire Effects Information System (FEIS). Retrieved from https://www.fs.fed.us/database/feis/plants/clubmoss/lycob
- Chopra, R. N., Nayar, S. L., & Chopra, I. C. (1956). Glossary of Indian Medicinal Plants. Council of Scientific and Industrial Research.
- Sen, U. & Chandra, S. (2000). Indian Pteridology at the New Millennium. Scientific Publishers.
- Puri, P. (1980). Bryophytes and Pteridophytes. Atma Ram and Sons.