(4] 



(5) 



The ability 

 reproductive 

 submerged. 



to complete 

 cycle while 



their 

 fully 



The ability to 

 other organisms 

 environment. 



compete with 

 in the marine 



Only a small, closely related group of 

 monocotyledonous angiosperms have evolved 

 all of these characteristics. 



Worldwide there are approximately 45 

 species of seagrasses that are divided 

 between 2 families and 12 genera. The 

 Potamogetonaceae contains 9 genera with 34 

 species, while the family Hydrocharitaceae 

 has 3 genera and 11 species (Phillips 

 1978). In south Florida there are four 

 genera and six species of seagrasses 

 (Table 2). The two genera in the family 

 Potamogetonaceae have been reclassified 

 comparatively recently and many of the 

 widely quoted papers on the south Florida 

 seagrasses show Cymodocea for Syringodium 

 and Diplanthera for Halodule . Recent dis- 

 cussion in the literature speculates on 

 the possibility of several species of 

 Halodule in south Florida (den Hartog 

 1964, 1970), but the best current evidence 

 (Phillips 1967; Phillips et al . 1974) in- 

 dicates only one highly variable species. 



The small species number (six) and 

 distinctive appearance of south Florida 

 seagrasses make a standard dichotonous key 

 generally unnecessary (Figure 4). General 



systematic treatments such as den Hartoq 

 (1970) and Tomlinson (1980) should be con- 

 sulted, however, when comparing the sea- 

 grasses of other areas. The best descrip- 

 tions of the local species are still to be 

 found in Phillips (1960). 



Turtle grass ( Thalassia testudinum ) 

 is the largest and most robust of the 

 south Florida seagrasses. Leaves are rib- 

 bon-like, typically 4 to 12mm wide with 

 rounded tips and are 10 to 35cm in length. 

 There are commonly two to five leaves per 

 short shoot. Rhizomes are typically 3 to 

 5 mm wide and may be found as deep as 

 25 cm (10 inches) in the sediment. Thalas- 

 sia forms extensive meadows throughout 

 most of its range. 



Manatee grass ( Syringodium f il i forme ) 

 is the most unique of the local seagrass- 

 es, as the leaves are found in cross sec- 

 tion. There are commonly tv;o to four 

 leaves per shoot, and these are 1.0 to 1.5 

 mm in diameter. Length is highly vari- 

 able, but can exceed 50 cm (20 inches) in 

 some areas. The rhizome is less robust 

 than that of Thalassia and more surfici- 

 ally rooted. Syringodium is commonly 

 mixed with the other seagrasses, or in 

 small, dense, monospecific patches. It 

 rarely forms the extensive meadows like 

 Thalassia . 



Shoal grass ( Halodule wriqhti i ) is 

 extremely important as an early colonizer 

 of disturbed areas. It is found primarily 



Table 



Seanrasses of south Florida. 



Family and species 



Common name 



Hydrocharitaceae 



Thai as s_i_a tes tudinum Ko n i g 



Halophil a decipiens Os ten fold 



Halophila onge lmann i Ascherson 



Halop'h ila johnsonii Eiseman 



Potanoqetonacca 



Turtle Grass 



Syringodium f il i forme Kut7 

 Halodule wriqhti i Ascherson 



Manatee grass 

 Shoal nrass 



