FLOWERING PLANTS OF THE WATERS AND SHORES OF THE GULF OF 



MEXICO 



By Robert F. Thorne, Department of Botany. State University of Iowa 



The maritime flowering plants of the Gulf of 

 Mexico, because of their dependence on light to 

 carry on photosynthesis and on the substrate to 

 furnish a place of attachment for their roots or 

 iniderground stems, are confined to shores and 

 shallow coastal waters. No flowering plant has 

 been reported from Gulf waters at depths greater 

 than 100 meters. Taylor (1928) reports that 

 Halophila engelmannii Asclicrs., a sea-grass, was 

 dredged in the transparent waters of the Dry 

 Tortugas area from measured depths up to 73.2 

 meters and one estimated depth of 91 meters. 

 Thus only the margins of the Gulf of Mexico are 

 of concern to one interested in vascular plants. 



Knowledge of the flora and vegetation of the 

 Gulf perimeter is mostly inadequate. Only in 

 very limited areas such as the Florida Keys is 

 information about the plant life extensive. Data 

 on the Gulf maritime flora must be sought in many 

 publications treating limited land areas fringing 

 the Gidf. The appended bibliography attempts 

 to bring together the more important and recent 

 of these references. 



Floristic works of the greatest usefulness in the 

 Gulf region because of their wide scope and rela- 

 tively recent publication are: Small's Flora of the 

 Southeastern United States, 1913, and Manual of 

 the Southeastern Flora, 193.'3, Leon and Alain's 

 Flora de Cuba, 1947-51, and Standley's Trees and 

 Shnd>s of Mexico, 1920-26, and Flora of Yucatan, 

 1930. Pertaining to smaller areas but often con- 

 taining much valuable information on the distribu- 

 tion of maritime plants are: Small's Flora of the 

 Florida Keys, 1913, Molir's Plant Life of Alabama, 

 1901, Lowe's Plants of Mississippi, 1921, Lloyd and 

 Tracy's The Lisidar Flora of Mississippi and 

 Louisiana, 1901, and Cory and Parks' Catalogue 

 of the Flora of the State of Texas, 1938. Floristic 

 and ecological treatments of still more limited 

 areas are referred to imder the several plant 

 communities. 



The marine and strand flowering plants of the 

 Gulf are best considered in the natural groupings 

 in which they usually grow. There are four such 

 major plant communities: submarine meadow, 

 mangrove swamp, salt marsh, and sand-strand 

 vegetation. 



SUBMARINE MEADOW 



Least collected and studied of all the Gulf plants 

 are the marine spermatophytes or sea-grasses. 

 These aquatic flowering plants, members of the 

 Hydrocharitaccae and Zannichelliaceae rather 

 than true grasses, have received some attention in 

 the waters around the Dry Tortugas. Bowman 

 (1916, 1918) and Taylor (1925, 1928) have con- 

 tributed original observations on the ecology and 

 morphology of species in that area. For other 

 parts of the Gulf information about them is scanty 

 (Howe 1918; Davis 1940; Hotchkiss 1940; Ste- 

 phenson and Stephenson 1950). Several authors 

 (Ascherson 1906; Ostenfeld 1914, 1926-27; Setchell 

 1920, 1934a) have discussed their world distribu- 

 tion, and Balfour (1878), Rydberg (1909), and 

 Bowman (1916) have contributed papers on their 

 morphology. The most thorough taxonomic treat- 

 ments of the marine spermatophj'^tes are included 

 in Ascherson and Graebner's (1907) monograph 

 of the Potamogetonaceae in Das Pflanzenreich 

 and Ascherson and Giirke's (1889) study of the 

 Hydrocharitaccae in Die Naturalichen Pflanzen- 

 familien. Descriptions and keys for the identifi- 

 cation of Gulf species are available in Small (1933) 

 and Muenscher (1944). 



More species of marine flowering plants are 

 found in the Gulf of Mexico and Caribbean Sea 

 than anywhere else in the Western Hemisphere. 

 Li the waters around the Florida Keys grow five 

 species belonging to two families: Diplanthera 

 wriyhtii (Aschers.) Aschers. and Syringodium 

 Jiliforme Kutz., manatee-grass, of the Zoster- 

 aceae, Thalassia testudinum Konig, turtlegrass, 



193 



