River Clyde Fisheries Management Trust Ltd.
 

Freshwater plants or weeds can be divided into two :

• Flowering
• Non-flowering (algae, mosses, liverwort and ferns).

Flowering plants

Divided into three categories by growth area.       

1. submerged weeds
2. weeds with floating leaves
3. emergent weeds

Submerged weeds  The submerged weeds, along with the floating leaf variety, are the true water plants or hydrophytes. Found where there is water as they will die quickly if exposed; commonly rooted in mud - Canadian pondweed (Elodea canadensis) other examples are the free floating (below surface) Hornwort (Ceratophllum).
All these flowering plants are submerged and only rise above water level to flower. 

Floating leaved weeds   Most of these are rooted in the lake or riverbed and have long, pliable stems. There are a number that are also free floating, such as Duckweed (Lemna), Bladderwort (Utricularia) and Water soldier (Stratiotes aloides).

These plants do float freely at the water surface; the bladderwort is one of the interesting plants as it is carnivorous, the leaves having hair like segments on which are born bladder-like traps which catch and digest prey.

The rooted plants in this category include the Broad-leaved pondweed (Potamogeton amphibium), Water crowfoot (Ranunculus aquatillis), Starwort (Callitriche stagnalis) and the Yellow water lily (Nuphar hutea).

Emergent weeds   This type of plant have erect aerial style leaves arising from open water or mud. These plants grow in situations where water level ranges from just below ground level to about half the maximum height of the plant. These are the larger erect type plants like the grasses (reeds). Part of the family of reeds includes the Common reed (Phragmites communis) these often form dense reed-beds around the margins; other plants in this community (similar to broad leaved plants) are the Water plantain (Alisma plantago-aquatica), Arrowhead (Sagittaria sagittfolia) and the Marsh marigold (Caltha pahuustris).

Flowerless plants

Divided into three categories by position in the plant chain.

1. Algae   There are two types that will interest us from the freshwater point and these are a) the Blue-green and b) the Green algae.
   a) This algae forms either in a gelatinous mass, filaments or as a single cell. They become abundant in nutrient rich waters in late summer, the algae forms a 'scum' or 'water bloom'. Some of them produce poisons that are dangerous to humans and fish.
   b) The green algae is the largest group of the freshwater algae; the main forms are the desmids, which are single celled plants; and the diatoms, single celled like the desmids but have a wall made of silica. Some free float others attach to plants and stones.
2. Mosses and Liverworts   Several species of moss are found covering stones, particularly in fast flowing streams. They are often the only plants present which provide shelter for many of the stream fauna. (mosses/liverworts)
3. Ferns & Horsetails   There are only a few aquatic forms of this type of plant life; two of the commonest are the Quilwort (Isoetes lacustris) which grows submerged in nutrient poor lakes of northern Britain and the Water horsetail (Equisetum fluviatile) which is to be found emerging from shallow waters and bogs/ponds.