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.
Definition of aquatic plants for this class - Vascular Hydrophytes (vascular = conductive tissue in higher plants, hydro = water, phytes = plants)
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 lists 6,728 species found only in the United States. 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.
Reed’s List is classified by three growth factors.
1. Obligate Plants = require a specific wetland environment to grow. These plants require saturated soils.
Example: Cattails (genus Typha) in Southern AZ Typha domingensis. In Northern AZ Typha latifolia.
2. Facultative = adapted equally to either wet or dry conditions. Vegetation adapted for growing in saturated soils or upland soils. Example: Cottonwood trees
3. Occasional = usually found out of wetland environment, but can tolerate wetlands.
*** Many of the same species are found around the world because the habitats are the same ***
Wetlands have become of a major conservation interest since the mid 1970’s. Before 1970’s they were considered a place of disease due to flooding and property destruction. 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 emergent and is the cause of the most controversy.)
Wetlands are made of two water purification systems the “Kidneys” and “Biological Supermarkets”. The kidneys to wetlands work by water being taken upland to a wetland on to a lake then on to an ocean making this an open system. This system removes nitrogen and phosphorous from the water making it ideal for wetland vegetation. Biological Supermarket is a water purification system as well as a support bases for food chains.
EPA Hydrophytes List (growth factors):
A) Plants rooted in the substrate
Emergent plants example: Cattail Typha domingensis. Plant production takes place mostly above the water with its roots buried in aggressive shallow water. No other vegetation can grow around these plants.
Rhizomatous - those with long petioles. Example: Water Lily (genus Nuphar) http://www.ewaterlily.com/cgibin/shop/cart.pl?db=data.file&category=WHITE+HARDY+LILY. This plant has a stem under the soil and the petiole lifts the leaf up to the waters surface
Stoloniferous - having a long stem. Example: Pondweed Potamogeton natans. http://nafoku.de/flora/htm/potanata.htm and http://honeybee.helsinki.fi/USERS/KORPELA/potamogeton_natans.html Pondweed has an erect stem leading to the surface with leaves growing along the stem and at the surface.
B) Submerged plants
Stem type - leaves on the stem. Example: Hydrilla http://aquat1.ifas.ufl.edu/hyvepic.html (also called Waterweed)
Rosette type - leaves all from a subterranean root or stock. Example: Vallisneria http://www.tropica.dk/55.htm
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) http://www.floridaplants.com/eflora/eichornia_crassipes.htm, Duckweed (Lemna) http://www.tropica.dk/129.html, Water Fern (Azolla) http://www.tropica.dk/013.html
Origin of Aquatic Plants:
Aquatic plants are secondarily adapted to the water. (algae - mosses - ferns - gymnosperms - angiosperms). The flower portion of the plant is above water where it is able to transport sugar from the atmosphere down into the water while water is transported up to the flower portion of the plant.
Examples of Aquatic Macrophytes are giant kelps http://www.goldenstateimages.com/big/1019.htm and seaweeds
Both ferns and angiosperms have aquatic forms.
Ferns have 5 aquatic families, with 200 known species. Azolla is an aquatic fern
1% of higher plants could be described as aquatic plants 250 + families of angiosperms
with 300,000 species. 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 http://www-bml.ucdavis.edu/spartina/home.html http://www.csdl.tamu.edu/FLORA/image/k4730800.htm and Phragmites
Cyperaceae - sedges including Cyperus http://florawww.eeb.uconn.edu/acc_num/198500152.html, Carex, and Scirpus.
Juncus - rushes, have a hollow stem.
There are different zonation patterns for fresh and saltwater plants. Freshwater zones have deep rooted plants, shallow rooted plants, emergent vegetation, floating attached plants, submerged plants, and floating plants. Saltwater zones have halophytes in the sand dune areas, mangroves, emergent grasses, and sea grasses. In saltwater zones, plants must adapt to high and low tides.