Sept. 3, 1996

Taxonomy that we have seen so far in this class:

Monocots-

1.  Typhaceae - commonly called the Cattail Family (aceae ending means family). 
     These are emergent, rhizomatons, found in fresh or brackish waters.
	Typha (genus) domingensis  (species) This is the species found in Az.
	Typha  latifolia 

2.  Potamogetonaceae - Pondweed Family.
     This family is rooted and submerged.
	Potamogeton  Pondweeds, many species are found.
	Ruppia  Widgeon grass, fresh or brackish waters.
	Zannichelia  Horned Pondweed, fresh or brackish waters.
	Zoestra  marine seagrass.
	Halodule marine seagrass.
	Cymodocea marine seagrass.
	Phyllospadix marine seagrass.

3.  Najadaceae - Niad Family.
      This family is also rooted and submerged, there is only one genus.
	Najas marina  spiny niad found in brackish waters.

4.  Hydrocharitaceae - Frogbit Family.
     This family is rooted and submerged, and is found in fresh and marine waters.
	Anacharis  densa  Waterweed, also called Elodea.
	Halophila  marine.
	Thalassia  Turtlegrass, marine.
	Vallisneria  Wild Celery, common duck food found in freshwater.

5.  Gramineae - Grass Family.
     Grasses can be identified by the swollen base of each leaf where it meets the stem.  
This     
     is called a ligule.  There are 22 genera, important ones are listed.
	Phragmites australis Giant Reed, similar to Arundo, found in freshwater.
	Paspalum  used as turf grass, found in fresh and brackish waters.
	Panicum  panicles.
	Zizania  wild rice.
	Spartina  marine, marsh cord grass.
	Distichlis  marine, saltgrass.
	Monanthochloe  marine, salt-flat grass.

6.  Cyperaceae - Sedge Family.
      Sedges have a characteristic fruit near the tip called an achene.  They also have a small    
      section of plant above the fruit called an involucre.  
	Scirpus  olneyi  Bulrush with a triangular stem found in fresh or brackish waters.
	Scirpus  validus  Great Bulrush, with a round stem found in fresh or brackish 
	waters.
	Carex  many sedge species.
	Cyperus  umbrella plant, bunch of involucres at the top.
	Cladium  sawgrass of the everglades.
	Eleocharis  spike rush.
7.  Lemnacea - Duckweed Family.
      This family is free-floating, minute and found in freshwater.  There are other genera                                             
      that are not listed here.
	Lemna  duckweed.

8.  Araceae - Arum Family.
      Arums are monocots, although some do not appear to have parallel veins (this may be 
a   
      modified leaf tip). 
	Peltandra   elephant ear, large arrow shaped leaves.
	Pistia  water lettuce, floating plant.
	
9.  Pontederiaceae - Pickerelweed Family.
	Eichornia  crassipes  Water Hyacinth.
	Pontederia  Pickerelweed.

Dicots -

10.  Ceratophyllaceae - Hornwort Family.
        This family has no roots.  The tips of this plant break off and settle to the bottom of a
        lake at the end of the fall season.  In spring, the tips grow out into new plants.  These     
        plants get very dense and form mats on the surface of the water. 
	Ceratophyllum  demersum  this is the only genus, there is another species.


Sept. 5, 1996

Adaptations to Aquatic Environments 

Aquatic plants evolved from terrestrial plants.  Like whales and other marine mammals, 
aquatic plants evolved from land back to aquatic habitats.   Aquatic plants modified 
terrestrial features to withstand emerged, submerged, or floating conditions. 

Types of Challenges

				Emergent		Submerged		Floating	

Aeration of Roots


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Sexual 
Reproduction



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Seed Germination


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Photosynthesis
(Gas Exchange)




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Salinity	


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Aeration of Roots - 

Oxygen is transmitted from the leaves to the roots and rhizomes by lacunae (air spaces 
forming channels in leaves, stems, and roots).  Lacunae also have a structural role. 
Lacunae take up about 60% of the plants volume.

An experiment was done to demonstrate the oxygen gradient in plants.  It was found that 
a plant has 20% oxygen in its leaves, 15% in its stem, 10% in the root parts, and only 2-
5% in the root hairs.  The oxygen is taken in from the air by photosynthesis and travels 
through the plant and out the root hairs.

When low oxygen levels are present, plants use other mechanisms to adjust for respiration.  
  Aquatic plants can respire anaerobically.  This has been shown experimentally by 
bubbling N2 or O2 into the water with rhizomes, and then measuring the ethanol 
production.  At <3% O2 , ethanol is produced by Typha, Scirpus, Nuphar, and others.
  Some aquatic plants have developed air roots along their stems for respiration in 
water.
  Aquatic trees have developed pnuematophores which are extensions of the root system 
reaching above the water level.  Pnuematophores take in oxygen through small holes 
at their tips.

Other  challenges that aquatic plants must adapt to include:
  flooding
  desiccation (drying out)
  nutrient uptake
  vegetative reproduction