Aquatic Plants  Aug. 28, 1997

Definition of aquatic plants for this class - Vascular Hydrophytes
(vascular = conductive tissue in higher plants, hydro = water, phytes = plants)

In this class we will look at aquatic plants, aquatic macrophytes, and wetland plants.
Aquatic plants are broadly defined as plants that normally grow in water, in soil covered 
with water, or soil normally saturated with water.

An EPA definition of a wetland is an ecosystem that needs constant or recurrent shallow 
saturation of substrate.  Diagnostic features are hydrophytic plants and hydric soils.

The EPA has put out a Hydrophyte List which currently has 6,728 species listed.  This 
includes 18 regional lists.  This list was started by the US Fisheries and Wildlife in the mid-
1970’s and has been supplemented by Reed’s “National List of Plant Species that Occur in 
Wetlands” in 1988. 

Wetlands are currently managed by the 50% rule which states that the vegetation must be 
50% hydrophytic in an area for it to be called a wetland.  The 50% rule has caused a lot of 
controversy in defining wetlands.  Hydrophytic vegetation can be obligate hydrophytic, 
facultative hydrophytic, facultative mesaphytic, or a facultative upland plant (this includes 
emergents and is the cause of the most controversy.)  An obligative plant is one that is 
confined to a particular environment, such as a wetland, while a facultative plant can be 
found in many environments.  

Aquatic plants discussed in this class:

A)  Plants rooted in the substrate

	1.  Emergent plants    
	example: Typha (genus) domingensis, also called Cattail. Plant production takes 
	place mostly above the water. 

	2.  Plants with floating leaves
	(i)  Rhizomatous - those with long petioles. 
	example: Water Lily (genus Nuphar) This plant has a stem under the soil and the 
	petiole lifts the leaf up to the waters surface.
	(ii)  Stoloniferous - having a long stem.
	example: Potamogeton (genus) natans, also called Pondweed  Pondweed has an 
	erect stem leading to the surface with leaves growing along the stem and at the 
	surface.
  
B)  Submerged plants

	(i)  Stemy type - leaves on the stem.
	example: Hydrilla (also called Waterweed)
	(ii)  Rosette type - leaves all from a subterranean root or stock.
	example: Vallisneria
	(iii)  Thalloid type - reduced body without leaves.
	example: Podostemmum  (this plant attaches to rocks in streams and waterfalls)

C)  Free floating hydrophytes - found in still waters.
	examples: Water Hyacinth (Eichornia crassipes), Duckweed (Lemna), Water Fern (Azolla)

Origin of Aquatic Plants

Aquatic plants are secondarily adapted to the water. 
(algae  -  mosses  - ferns   -  gymnosperms  -  angiosperms)

1% of higher plants could be described as aquatic plants

Both ferns and angiosperms have aquatic forms.  

Ferns have 5 aquatic families, with 200 known species. Azolla is an aquatic fern.
  
Angiosperms divide into monocot and dicot families.  There are 10 dicot families, with 
300 species.  The Water Lily, mangroves and Ceratophyllum are examples of aquatic dicots.
There are 18 monocot families, all 
marine aquatic plants are monocots. 
Common monocots are Zoestra, Potamogeton, 
Pondweed, Ruppia, Lemna, Typha, and Naja.


Families that have many hydrophytes:

Graminae - grasses including reeds, Spartina, Phragmites.

Cyperaceae - sedges including Cyperus, Carex, and Scirpus.

Juneus - rushes.

There are different zonation patterns for fresh and saltwater plants.  Freshwater zones 
have deep rooted plants, shallow rooted plants, emergents, floating attached plants, 
submerged plants, and floating plants.  Saltwater zones have halophytes in the sand dune 
areas, mangroves, emergent grasses, and seagrasses.  In saltwater zones, plants must adapt 
to high and low tides.