The writer, then, recognizes four fairly marked associations in the general Tortugas flora of strand plants : (1) the Uniola community : (2) the Suriana community; (3) the Opuntia community; (4) the Chamcesyce community.
The first association, the Uniola community, is rather heterogeneous and varies slightly on different beaches, depending on the conditions in rough weather and the prevailing winds. The lowest on the beach and close to the high-tide limit is Calcite lanceolata (Wildenow) O. E. Schulz. The dried stalks of this may be seen in July, and during August they are uprooted and blow about the beaches as tumble-weeds. Growing with Cakile is the sand-spur, Cenchrue incertus M. A. Curtis, which forms large flat mats on the beaches, bearing its spikelets in a heavy spiny involucre, making a painful wound if stepped upon. Associated with this in dense masses the sea purslane (Sesuvium portulacastrum L.) is often seen; resembling it superficially is Alternanthera maritima St. Hildmann. Back from the reach of spray is Sporobolus virginicus (L.) Kunth; frequently out in line with it is Tournefortia gnaphalodes (Jac quin) R. Brown, forming large characteristic, flat-topped bushes 1 to 1.5 meters tall, clothed with soft, whitish-gray, tomentose leaves. The long, trailing vines of the purple beach morning-glory, Ipomea pes-caprce (L.) Sweet, are found here, and also Sccevola plumieri Vahl, in clumps with thick, glossy leaves, nauseating black berries, and white blossoms with the peculiar corolla split down one side and the odd ciliated indu sium on the stigma. This last is one of the most singular of all the plants of the region. On the higher portions of the beaches and a meter or two back from the water-line, sea oats, Uniola paniculata L., will be observed, a grass about 2 meters tall, with a gracefully drooping panicle of heavy spikelets. This grows in rather close formation over large areas, forming thick tufts as it grows from season to season, and the dead culms remain clustered about the living ones.
like a sort of a mossy covering on the twigs.
The third association is the Chamcesyce group, which also covers large areas on some of the keys, its members growing in situations not so suitable for the previous group. The chief component of the association is Chamcesyce buxifolia (Lamarck) Small. This spurge forms tracts thickly covered with its small gray-green boxwood-like leaves and tough brown stems filled with abundant latex. The rooting sys tem of the plant is remarkable; a small individual, only 3 decimeters tall, may have a root system 9 decimeters in diameter, and were the plants growing in a soil less loose and coarse than the Tortugas sand they could scarcely be pulled up by a strong man. An ally of the Chamesyce is a composite, the marsh elder, ha imbricata Walter, which forms a rather tall bush, about 10 to 15 decimeters, with small, light-green succulent leaves, which have a rather pleasant bitter, acrid odor and heads of yellowish, inconspicuous flowers. A third member of this group is a sedge, Cyperus brunneus S. Watson, forming con spicuous tufts of grayish foliage overtopped by the deep-brown inflorescences.
The fourth association is the Opuntia community. This is made up mostly of Opuntia dilienii (Ker) Haworth and Paspalum ccespitosum Flugge, a rather coarse grass about 4 decimeters tall, the branched inflorescence prolific with dark-brown, disk-shaped seeds. Frequently occurring in this association, and also to some extent in the Chamozyce community, are three species common in the Tortugas: (1) the Iponuea pes-caprce; (2) its more beautiful relative, the white moon-flower, Calonyction tuba (Schlechtendal) Colla, which makes a most wonderful effect in the brilliant tropical moonlight with its large salver-shaped corollas starring-over the clumps of Opuntia or other supporting vege tation, half hidden in its enveloping heart-shaped foliage; (3) Melon thera bretrifolia 0. E. Schultz, a scrubby composite about 6 decimeters tall, bearing inconspicuous whitish blossoms, but during the hot mid dle portion of the day they are constantly surrounded by hosts of a tiny butterfly, Thecla, whose source of food is the nectar of these little flowers. Into the above four groups the predominating species of the Tortugas may be said to fall naturally on account of the influence of various factors in the environment or those inherent in the plants themselves.