What are seagrasses?
Seagrasses are the sole marine representatives of the Angiospermae. They all belong to the order Helobiae, in two families: Potamogetonaceae and Hydrocharitaceae. The currently accepted hypothesis of the origins of seagrasses is that they derived from terrestrial plants which returned to the sea (den Hartog, 1970).
There are currently some 58 species recognised, in 12 genera, of which Australia is home to 30 - more than half. The origins of the seagrasses appear to have been around the ancient Tethys Sea, bounded by Africa, Gondwana and Asia, around 100 million years ago. By the Eocene, the seagrasses appear to have dispersed widely in the Asian-Pacific and the neo-tropics. The climatic changes accompanying the tectonic plate movements of the Cretaceous appear to have resulted in significant distributional changes, as temperatures have dropped. There is considerable evidence that major extinction events have occurred in the past, suggesting that seagrasses as a group may be declining.
Although they may occassionally be exposed to the air, they are predominantly submerged, and their flowers are usually pollinated underwater. A notable feature of all seagrass plants is the extensive underground root/rhizome system which anchors them to their substrate. Seagrasses are commonly found in shallow coastal marine locations, salt-marshes and estuaries; in the tropics they are often found associated with mangroves.
|
The Western Australian Seagrass Web
pages were created and are maintained by: Murdoch University Western Australia. Last update: Tuesday, 25 October, 2005 10:12 |