Lycopodium

Lycopodium: Internal and External Structure

Systematic Position

• Division- Pteridophyta
• Class- Lycopsida
• Order- Lycopodiales
• Family- Lycopodiacelae
• Genus- Lycopodium

Distribution and Habitats

Lycopodium is commonly known as Club moss, includes about 200 species which are distributed in the tropical regions of the world, a few are found in temperate regions. The species are usually herbaceous but L. selago is shrub like. A few species are erect, while others grow as creepers or epiphytes. Most of the species of Lycopodium prefer moist and shady places, rich in humus and other organic matters. Chowdhary (1937) has reported eight species of Lycopodium from India which are L. clavatum, L. cernuum, L. hamiltonii, L. phlegmaria, L. serratum, L. setaceum, L. phyllanthum and L. wightianum. Among these species L. phlegmaria is epiphytic which grows on the trunk of the trees etc. Engler and Prantl (1902) have splitted the genus Lycopodium into two sections i.e. (i) Urostachya-In which branching is always dichotomous and roots originate only from the base of the stem, (ii) Rhopalostachy-In which the stems are prostrate bearing upright branching and the roots are adventitious which arise along the stem.

Sporophyte

External Morphology

The plant of Lycopodium is sporophyte which is differentiated into root, stem and leaves. The leaves are sessile, simple and eliguate, which have mid rib. The strobili of L. serratum and L. phlegamaria are not compact whereas they are compact in L. clavatum and L. cernuum.

1. Root:

   The adventitious roots arise from the lower most part of the plant, they go into the soil and keep the plant erect and absorb water. In L. clavatum and L. cernuum the roots are branched.

2. Stem:

   It is usually dichotomously branched on which leaves are arranged.

3. Leaves:

   They are about 2-10 mm long, with one mid rib in each leaf. Shape is lanceolate. In L. clavatum, the leaves are spirally arranged but in L. alpinum, L. cernuum and L. complanatum leaves are arranged in whorls. In L. mandioccanum, heterophyllous leaves are found, which may 20-35 mm. long, while other leaves are smaller in size.

Anatomy or Internal Structure

Anatomy of Stem

In T.S. the stem of Lycopodium is differentiated into epidermis, a broad cortex and a central vascular cylinder or stele.

1. Epidermis:

   The epidermis is a single outermost layer of small cell with the outer and often radial walls thickened and cutinized, it is provided with numerous stomata.

2. Cortex:

   The cortex either may be homogeneous throughout and made up of parenchymatous cells or may remain divided into three concentric zones, the outer cortex of simple parenchyma : middle cortex is made up of sclerenchyma and inner cortex of parenchyma, as in L. cernuum. In case of L. clavatum, the outer and inner cortex is sclerenchmatous and middle one is parenchymatous.

3. Endodermis:

   Below the cortex single layered endodermis is present, casparian strips are found in endodermal cells.

4. Pericycle:

   It is 2 or 3 layered situated below the endodermis. It is made up of thin walled cells.

5. Stele:

   The stele of Lycopodium stem is protostele with a central xylem surrounded by phloem without any pith. But any how there is a good deal of variation in the arrangement of the vascular elements.

There are commonly three types of stele in different species of Lycopodium:

1. In some species like L. serratum and L. phlegmaria xylem forms radiating arms from the centre, with alternating phloem this is called as actinostele.
2. In other species like L. cernuum the xylem is broken up into isolated strands which are irregularly mixed with phloem this is called mixed Protostele.
3. In still other species as in L. clavatum, L. volubile xylem and phloem occur in alternating more or less parallel bands, this is called Plectostele.

In Lycopodium, xylem is always exarch and consists of a few tracheids, and phloem consists of sieve tubes and phloem parenchyma. As the stele lacks cambium therefore there is no secondary growth.

Anatomy of Root

In T.S., it shows the following structures :

1. Epiblema:

   It is single layered outermost, made up of thin walled cells, unicellular root hairs are also present.

2. Cortex:

   It is broad, present below the epiblema, multilayered and parenchymatous, the outer cortex is sclerenchymatous.

3. Stele:

   It is di-arch in which xylem is ‘C’ shaped. On both the ends of metaxylem protoxylem is seen. Actually there are seven to ten patches of protoxylem and corresponding metaxylem masses often unit in the center presenting a stellate form with the phloem between the rays. Stele is surrounded by well defined endodermis.

Anatomy of Leaf

A transverse section of leaf is differentiated into Epidermis : which is the outermost layer of one cell thick and is highly cutinized, interrupted by stomatas, in the centre there remain present a vascular bundle which is amphicribal type and remains surrounded by sclerenchymatous pericycle. In between the vascular bundle and stele the homogeneous parenchymatous mesophyll remains present which does not show any differentiation of tissues.

Important links

• ‘Telome Theory’ of Sporophyte Evolution in Pteridophytes
• Economic Importance of Pteridophytes
• Origin & Evolution of Pteridophytes (Vascular Cryptogams)
• Alternations of Generation in Pteridophytes (Origin, Theories)
• Apogamy and Apospory
• Stele in Pteridophytes: Meaning, Types & Its Evolution
• Characteristic Features of Pteridophytes

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