In their large area of geographic overlap, White Mangrove (Laguncularia racemosa) and Black Mangrove (Avicennia germinans) both have erect breather roots (pneumatophores) protruding up out of the water, but those of White Mangrove are fewer in number, wider, and more often branched. White Mangrove grows landward of Red Mangrove (Rhizophora mangle), which has conspicuous prop roots, and Black Mangrove. It often occurs onshore with Buttonwood (Conocarpus erectus, like White Mangrove a member of the plant family Combretaceae), which may be easily distinguished from White Mangrove by the fact that Buttonwood has alternately arranged leaves and leafstalk glands that are less prominent than those of White Mangrove. (Petrides 1988) The position and appearance of the glands on both the petiole and on the leaf blade differ conspicuously between White Mangrove and Buttonwood (see images on this page and on the Buttonwood page).
An excellent resource for identifying the mangroves of Florida can be found at http://www.selby.org/
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