GULF OF MEXICO 



195 



mangrove swamp in other regions are listed in 

 tlie l)il)liography for Jamaica (Steers et al. 1940), 

 tlie Virgin Islands (B0rgescn 1909; Raunkiaer 

 1934), Micronesia (Fosberg 1947), Indo-Malaya 

 (Schimper 1891), and for the tropics in general 

 (Schimper and Faber 1935) and (Warming 1909). 



The three widely distributed mangroves of 

 Gulf shores are RMzophora mangh L., the red 

 mangrove, Avicerinia nitida Jacq., the black or 

 honej^ mangrove, and Laguncularia racemosa (L.) 

 Gaertn. f., the white mangrove. These species 

 grow mixed together or in distinct zones. All are 

 noteworthy for their ability to withstand varying 

 concentrations of salt in the sea water and soil 

 solution in which their roots are buried. They 

 are apparently facultative halophytes, for seed- 

 lings of each have been grown in fresh soil and 

 water for. at least 6 years (Davis 1943). Rhizo- 

 phora may be readily identified by its peculiar 

 system of branching prop-roots extending down- 

 ward like stilts from the trunks and lower branches 

 and by the less common flexible air roots dropping 

 from the upper branches. It produces seeds which 

 germinate while attached to the tree to form 

 club-shaped hypocotyls commonly 30 centimeters 

 long. These hang by the two cotyledons from 

 the ovate fruit until they plummet into the water 

 or mud below the tree. Avicennia produces an 

 abundance of odd, pencil-like pneumatophores 

 rising through the mud from the shallow hori- 

 zontal roots. The flowers produce abundant 

 nectar that is manufactured by bees into excel- 

 lent honey. The fruit is ellipsoid, flattish, and 

 3 to 5 centimeters long. Laguncularia produces 

 fewer and smaller pneumatophores than Avicen- 

 nia. It may be recognized by its fleshy, elliptical 

 leaves and small, ribbed fruit. 



In addition to the three mangroves several 

 plants are characteristic of mangrove swamps. 

 A relative of Laguncularia, Conocarpus erecta L., 

 called the buttonwood or button mangrove be- 

 cause of its small, button-like or alder-like clusters 

 of flowers and fruit, grows inland from the other 

 mangroves on harder ground that is usually not 

 flooded by normal tides. Its trunks are loose- 

 barked, twisted, and frequently prostrate. It is 

 a common plant also in dune hammocks. Two 

 vine-like shrubs of the Leguminosae, Caesalpinia 

 crista L., nicker-bean, and Dalbergia ecastophyllum 

 L., coin-vine, often sprawl over the mangrove 



259534 O— 54 14 



thickets on their landward margin. Both species 

 are more shrub-like when growing on the dunes. 

 Another vine, of the grape family', Cissus incisa 

 (Nutt.) Desmoul., marine-ivy, climbs tlirough 

 the crowns of tlie mangroves and sends down to 

 the ground long, cord-like aerial roots. Batis 

 maritima L., saltwort, a succulent-leaved, spread- 

 ing or prostrate shrub, is frequently the only 

 species accompanying the mangroves on wet mud. 

 On sandy or marlj^ shores other succulent halo- 

 phytes, such as Salicornia virginica L., glasswort, 

 Sesuvium portulacastrum L., sea-purslane, and 

 Suaeda linearis (Ell.) Moq., sea-blite, and several 

 grasses may cover the groimd on the inner margin 

 of the mangrove thickets. 



On drier ground landward from the mangrove 

 thickets several shrubs and herbs associated with 

 Conocarpus form an open thicket transitional to 

 shore hammock or pineland. Some of the plants 

 of this transitional zone, flooded by salt water 

 only during spring and storm tides, are Borrichia 

 frutescens (L.) DC, sea-oxeye, Lycium carolini- 

 anum Walt., Christmasberry, Bumelia celastrina 

 HBK., saffron-plum, Coccoloba uvifera (L.) Jacq., 

 sea-grape, Maytenus phyllanthoides Benth., and 

 Sophora tomentosa L., necklace-pod. In addition 

 to these, all found m the Tampa Bay region of 

 central Florida, several other tropical associates of 

 Conocarpus in the mangrove-hammock transition 

 zone are found m the more tropical part of southern 

 Florida and the Florida Keys. These are Bor- 

 richia arborescens (L.) DC, sea-oxeye, Rhab- 

 dadenia biflora (Jacq.) Muell. Arg., rubbervine, 

 Capparis flexuosa L., Achras emarginata (L.) 

 Little, wild dilly, Jacquinia keyensis Mez., Joe- 

 wood, Torrubia longifolia (Heimerl.) Britt., blolly, 

 Erythalis fruticosa L., Acrostichum aureum L., 

 leather fern, and several cacti, Acanthocereus 

 floridanus Small, dildoe, Harrisia simpsonii Small, 

 prickly-apple, and Opuntia dillenii (Ker) Haw, 

 prickly-pear. The loose bark of Conocarpus fur- 

 nishes a foothold to several epiphytes including 

 Epidendrum tampense Lindl., an orchid, and 

 various species of Tillandsia, the air-pines. 



Zonation in mangrove swamps appears to be 

 correlated with water level and degree of salinity 

 of the water and substrate and in some areas with 

 tidal fluctuations. Each species, however, may 

 be quite variable in relation to these factors. 

 Rhizophora may form colonies well off shore on 



