Limnology (2+1)

Practical No. : 13

Collection and identification of aquatic plants from different freshwater bodies
The plants vary greatly in the degree to which they have become truly aquatic and present in an interesting series of gradations from those which are little more than amphibious, living at the edge of the water in very moist or water saturated soil. Aquatic plants are those unwanted and undesirable vegetation which reproduce and grow in water and if left unchecked may choke the entire body of water posing a serious menace to pisciculture. Another definition is that the surplus growth of a plant that influences adverse physical, chemical and biological effects on a water body with its resultant economic and aesthetic losses.

Collection of Aquatic plants
The aquatic plants can be collected using a long handled hook, nets or by hand. For quantification of sample in a given area the floating or sinking type of quadrates of known size namely (1m x 1m or 0.5m x 0.5m) made up of PVC pipes or wood are used. These quadrates are placed to mark the area from which sample is to be taken. After collection, these plants are brought to the laboratory for identification. Before identification of these plants, they must be classified based on their habitat into the following classifications, they are :
i. Floating macrophytes
ii. Marginal macrophytes
iii. Submerged macrophytes
iv. Emergent macrophytes

Identified of plants using the following keys :
i. Floating macrophytes
1. Eichhornia sp (Water hayacinth or blue devil)
Class : Angiosperm
Family : Pontederiacea
It is native of Brazil, accidentally brought to India and released in West Bengal, one of the most damaging aquatic weeds, inhabits stagnant and slow moving rivers.
Leaves broad with swollen stalks filled with air to enable them to float on water surface, dense leathery roots, flower pinkish in colour, multiplication by vegetative propagation, dries off in winter and spourts during summer.
2. Salvinia (water fern velvet)
Family : Salviniaceae
This plant has got rhizome, stalk or stem is delicate, oblong or hemispherical leaves, actual roots absent, leaves sessile with short stalk, leaves in two or more whorls, second whorl is either lateral and floating, third one submerged in water which looks like roots, lateral leaves sometimes filled with air which aids in floating.
3. Pistia (water lettuce)
Family : Araceae
A free floating perennial plant, plant body comprise a shell like rosette of tongue shaped leaves, reduced stem, sessile leaves and numerous branching roots, leaves form common cup shaped structure, leaves ovate and surrounded at the base by membranous sheath.
4. Lemna (duck weed)
Light green in colour, occurs in group of one to three, no distinct stem, leaves have flattened, minute leaf-like fronds, vegetative reproduction is rapid, often forming a scum over the surface, flowers are rare and so small that they are invisible to naked eye, appear as small weeds.
5. Azolla (water velvet)
Family : Azollaceae
Smaller plant, found in stagnant water bodies, leaves lobed, scale like, thick and about 0.5 mm in length, the entire plant is 1.5 – 2.0 cms in length, impart reddish green colour to water surface by covering it, it fixes atmospheric nitrogen.
ii. Marginal macrophytes
1. Colocasia
Family : Araceae
This plant covers large areas of the water body, leaves ovate, 6-20 inches long and 3-12 inches wide, leaf margin dark green in colour, base of stem triangular, petiole long up to 3-4 inches, colour of petiole green, violet or purple.
2. Typha (Cat tail or Elephant grass)
Family : Typhaceae
Common in margins of ponds, lakes, rivers and canals, perennial, creeping rhizome with leaves growing up to 2 m height and leaves have sheath at the base. Leaves bi-serrate, thick and spongy, secreting organ present at the leaf base, flower numerous and cylindrical.
3. Marsilea (water shamrock)
Family : Marsiliaceae
It inhabits ponds, rooted in shallow and stagnant waters, roots slender, stalks slender and thin, roots burrowed into the ground, petiole long with four cloves like or sharp pointed leaflets.
4. Scirpus (Bullrush)
Family : Cyperaceae
Annual herb, triangular in cross section, stem bears sheath at the base but sometimes leafy and naked, spiklets numerous with one or more long leaves from the base of branch, spiklets are usually with more flowers.
5. Cyperus (Flat sedges)
Family : Cyperaceae
Perennial herb with a single stem, cylindrical in cross section and hallow. The stem has sheath at the base and with one or more leaves on top forming a cluster, flowers or spikltes are present at the top.
iii. Submerged macrophytes (Rooted)
1. Hydrilla
Family : Hydrocharitacea
It is found to occur in almost all water bodies in India like ponds, lakes tanks etc. Leaves linearly arranged in whorls while stem is slender, grows up to 45 cms, has got fibrous roots, multiplies very rapidly by spores and vegetative propagation, infestation density is 20-30 kg per square meter, broken parts of this plant develops into a new plant by attaching themselves with the help of roots, provides shelter to young fish in aquaria offer a substrate for attachment of spawn of common carp.
2. Chara (stonewort)
Occurs in all types of freshwater bodies, stem has got erect branches and are gregarious in habit, nodes and internodes can be easily distinguished, grow up to 15 – 30 cm in length, remains unattached to the bottom, plant is rough to touch.
3. Vallisneria (eel grass / tape grass)
Plant with long ribbon like leaves measuring 0.5 – 1 m width, female flowers are long, thread like, twisted and appear at stalks, propagation is by offshoots, it can tolerate temperature of 25 – 30^oC and medium water hardness.
4. Ceratophyllum (Horn wort) - (Non-rooted)
It has got a fragile algal like structure, grows to about 80 cms in length, roots are lacking, leaf branches are sometimes modified into rhizoids, lower part of stem serves as an anchore and helps in the absorption of nutrients, leaves are set in whorls, repeatedly forked with minute teeth on the side of the segment.
5. Cobamba (Fan wort)
Leaves are opposite, cut into thread like regions, stem slender with a gelatinous lining; plant provides shade and shelter for small organisms and forms a beautiful aquarium plant.
iv. Emergent macrophytes
1. Nymphaea (Water lily / Nilkamal)
Found in ponds, lakes, canals and also in water up to 1.5 m depth, perennial herb, petiole with lower end of leaflet, leaf round, veins radiating from the centre, leaves float on the surface of water, flower white or pink and solitary.
2. Nelumbo (Lotus)
Perennial herb, inhabiting tanks, ponds, lakes and other stagnant water bodies, leaves almost brown and are raised well above the water surface when mature, petiole attached to the centre of leaf, veins prominently radiate from the centre, flower large pinkish red leaf diameter ranging from 30 to 90 cms.
3. Trapa (Water chestnut / Singhara)
A perennial herb, occurs commonly in wild waters, leaves floating, solitary, branched or rhomboidal in shape, petiole with spongy swelling, flowers are solitary projecting over water surface, nuts with two or four sharp spines.
4. Myriophyllum (Parrot head / Water milfoil)
Found in stagnant and slow moving waters especially in places which are sheltered from wind, plants with slender, sparingly branched floating system mostly rooting freely at lower nodes, leaves opposite or whorled, the emergent leaves are horn like, flowers are very small and sessile and found in the axis of upper, emergent leaves grows to moderate height.
Other emergent type of plants are Nymphoides (Floating or Tringed water lily), Nuphar (Yellow lily or Cow lily) etc.