In Florida, Red Mangrove (Rhizophora mangle) can be most obviously distinguished from Black Mangrove (Avicennia germinans) and White Mangrove (Laguncularia racemosa) by the fact that these latter two species have numerous (especially Black Mangrove) erect breather roots emerging from the water, as well as by the Red Mangrove's distinctive seedlings attached to the parent. Gray Mangrove (or Buttonwood, Conocarpus erectus) has alternately arranged leaves, in contrast to the opposite leaves of the Red, Black, and White Mangroves. (Petrides 1988)
An excellent resource for identifying the mangroves of Florida can be found at http://www.selby.org/
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