Natural Vegetation of St. Croix

Coastal vegetation

Coastal vegetation can be subdivided into mangrove vegetation along sheltered, muddy coasts; seashore vegetation on sandy, open coasts; and vegetation along the rock coasts.

Mangroves grow partly in shallow seawater and partly on low, moist, saline bottoms from which water has drained. Scattered areas of individual trees are far from the shore. With increasing proximity to the shore, the trees become larger in size and aggregate into small clusters that eventually merge into a forest. The mangrove forest is composed of three species:

• White Mangrove, Laguncularia racemosa, ;
• Black Mangrove, Avicennia germinans; and
• Red Mangrove (or mangle tree or mangle baum), Rhizophora mangle .

The mangrove's sequence of succession creates a pattern of zonation in which the pioneer red mangrove is at the waters edge, black mangroves occupy a zone behind and white mangroves are more inland, but still in sandy soil. Red mangrove's distinctive prop roots provide hiding places for a wide variety of marine animals. Mangrove prop roots also trap leaf debris, sediment and storm water runoff. This helps protect water quality offshore. Black mangroves are distinguished by their "snorkel" roots, which protrude up through the soil and shallow water to absorb oxygen from the air.

A transitional area, behind the mangrove vegetation, consists of Buttonwood, Conocarpus erecta, a small tree or shrub . Also in this area is another small tree or shrub, Annona glabra, which is commonly called bunya, alligator or swamp apple. This shrub has a yellowish, edible fruit. Bucida buceras and the large swamp fern, Acrostichum danaeifolium, grow in areas where small streams empty into lagoons.

The Ipomaea pes caprae vine grows on tropical beaches. It can be several feet long and it creeps along the shore, sending roots into the sand. Interspersed with areas of this plant are several types of grasses that have a bluish-green hue. A few fleshy plants, such as sea purslane (Sesuvium portulacastrum), salt weed (Blutaparon vermiculare), and wolf’s milk (Chamaesyce buxifolia) are also found along the beach.

Bay lavender or black tea, Argusia gnaphalodes, is a shrub that grows in the most exposed areas. It can attain a height of more than three feet and can form a thick, impenetrable wall that faces windward. Other shrubs include Bay Cedar, Suriana maritima, which has thick, upward-pointing leaves, and Ernodea littoralis, which has narrow, elliptical leaves that are pointed at both ends.

Seagrape, Coccoloba uvifera and Manchineel tree, Hippomane mancinella, grow near the sea. In exposed areas, seagrape is no more than a shrub. In protected areas, it can attain a height of more than 20 feet. The leaves are stiff and leathery. Manchineel is tall and has a large trunk with shining, dark-green foliage. The milky sap of this tree and its fruit are powerful irritants. Some people and animlas are very susceptible to the irritating effects of contacting or ingesting the sap or fruit. The non-native coconut palm, Cocos nucifera, is also found on these forested, sandy beaches.

Except in the most wind-swept areas, the shrubs or low forest vegetation found on sandy beaches are also found on rocky coastlines. One additional plant in these areas is the fragrant white frangipani, Plumeria alba. This plant has thick branches and leaves that have a whitish color on the underside of the end of the branches. Also present are other species of the genus Coccoloba, which have somewhat smaller leaves than the seaside grape.

The Turk's Head cactus (Melocactus intortus), Organ Pipe cactus (Stenocereus peruvianus) and Agave spp. are commonly found along rocky shorelines and back-beach areas on the east end of St. Croix.

Thicket Vegetation

Thicket vegetation is commonly known as “bush.” It is well developed in the eastern part of St. Croix. The vegetation is dominated by Croton flavens, Croton betulinus, and Croton astroites. It also consists of other types of shrubs, primarily species of the genus Lantana, Wedelia fruticosa, Corchorus hirsutus, and Melochia tomentosa. All of these plants have hairy leaves, and some lose their leaves in the dry season. The introduced wild cotton plant, Gossypium barbadense, has become naturalized and is also common.

There are a few trees that typically grow in the thicket, especially in areas where moisture is more abundant. One is the Calabash Tree, Crescentia cujete, that has thick, stiff, and wide branches. It bears large, hard-shelled, gourd-like fruits. Other trees in the thicket include sugar apple, Annona squamosa, Acacias farnesiana and Acacia tortuosa, or casha, and Haematoxylon campechianum, locally known as logwood or Campeachy tree.

In areas where moisture conditions are more favorable, the shrubs in the thicket increase in size and the trees increase in number. These areas are called “thicket woods,” and they are fairly common on St. Croix. In contrast to the thickets dominated by Croton species, the thicket woods consist largely of wild tamarind, or tan-tan (leucaena leucocephela) that have a dark green color and are often covered with showy flowers after rains in the spring. The thicket woods are composed of several species of plants. They are generally dense and are often impenetrable. Barbed and spiny plants such as catch-and-keep, Acacia retusa, several species of cacti, and penguin or wild pineapple (Bromelia penguin) make these areas difficult to traverse.

Several species of epiphytes or "air plants" and true parasites are found in the thicket woods. Old man's beard, Tillandsia recurvata, and Air Plant, Tillandsia utriculata, of the pineapple family clasp branches with short and slightly developed roots. They have special leaf pores that absorb atmospheric moisture curved leaves that funnel moisture from dew and rain and store it in large hollows at the base of the leaves. A few orchids, primarily Christmas orchid, Epidendron ciliare, grow in these areas. They have thick, club-shaped stems in which the plant stores water for use in periods of drought. Dodder, Cuscuta americana, is a common parasitic vine that covers shrubs and trees with a thick network of yellow, thread-like branches.

Forest Vegetation

A few areas of forest vegetation are on St. Croix. The Silk Cotton or Kapok tree, Ceiba pentandra, is a dominant species in these areas. It has a large trunk, which has high roots that extend from all sides. Its name is derived from the soft, silky down, known as kapok, which covers the seeds and the inside of the capsules. Being deciduous, it sheds its leaves and is usually bare during the months of February and March. Its primary branches are very thick and covered with epiphytes.

Other large, deciduous forest trees include the Hog Plum, Spondias mombin, which attains a considerable size and bears a yellow, edible fruit; and the Sandbox tree, Hura crepitans, which is a tall tree that has a slender trunk studded with large thorns. The sandbox tree bears a capsular fruit that, upon ripening, bursts with a loud noise and hurls seeds in all directions. The Turpentine tree, Bursera simaruba, distinguished by its red, peeling bark, can also be found in drier forest areas.

Evergreen trees include the Strangler or Spotted-leaf Fig tree, Ficus citrifolia, which can grow to a very large dimension [circumference] and is distinguished by numerous aerial roots that hang down from the tree's branches. At ground level, the roots increase in thickness and often unite with one another, giving the appearance of individual trunks. The seeds of the Strangler fig tree commonly germinate on another tree, often at a considerable height from the ground. The fig tree attaches to the supporting tree while many of its roots grow to the ground. These roots then surround the host tree and eventually kill it. The Autograph or Wild Mammee tree, Clusia rosea, grows in the same manner. Other evergreen trees include the introduced Mesple tree, Manilkara zapota, and the Soursop tree, Annona muricata. They bear edible fruits. The Star apple, Chrysophyllum cainito, has leaves that are a golden color on the underside, and the Cashew, Anacardium occidentale, produces an edible nut. In most of the valleys along water courses, St. Croix's endemic Royal ("Cabbage") Palm, Roystonea borinquena, is common.

The forest understory vegetation consists of numerous smaller trees and shrubs. The Guavaberry, Myrciaria floribunda, and the Bay Rum tree, Pimenta racemosa, are small aromatic trees. Bay oil is distilled from the leaves of the bay rum tree. In the wooded regions of St. Croix, mostly north of Blue Mountain, the Trumpet Wood tree, Cecropia schreberiana , is one of the main species. This tree is rare on the other islands.

Freshwater Vegetation

No natural lakes or ponds occur in St. Croix, and most of the water courses are dry during most of the year. The Kingshill Gut on the southern side of St. Croix is an exception. It forms a few small pools that contain some species of freshwater vegetation. Nymphaea ampla, a waterlily that has white flowers, is common in these areas. Duckweed, or Lemna minor, floats on the surface of the water. Along the edges of the pools are several grasses and sedges of the genus Cyperus.

*Information excerpted from the 1998 Soil Survey of the United States Virgin Islands and the 2005 Island Peak to Coral Reef: Field Guide to the Plant and Marine Communities of the Virgin Islands.