Although they grow rapidly and quite tall (25 meters, 75 feet, or larger), she-oaks are minimalist trees able to survive under stressful environmental conditions. Unlike cactus and succulents, or tropical grasses which have alternate photosynthetic pathways (CAM, C4) to survive heat and drought, she-oaks survive because of their morphology (structure).
The leaves are greatly reduced, scale-like, arranged in whorls around the branches. The plants are leptocauls, "thin stems"—the task of photosynthesis has been taken over by the abundant slender evergreen branches. These branches are often mistaken for pine needles, hence the American name.
Like the leaves, the flowers are also reduced—sepals and petals are gone and replaced by bracteoles (small bracts). The flowers are separated into staminate (male) with a single stamen and pistillate (female) with a single style and two stigmas. The male flowers are arranged into spikes or catkins; the female are arranged into spherical or barrel-shaped heads.
Some Casuarina species are monoecious—staminate and pistillate flowers on a single plant; some are dioecious with the male and female flowers on separate plants. The head of female flowers becomes woody and cone-like when the seeds are ripe.
She-oaks regularly shed the thin branches. The ground beneath a stand of the trees is bare of other vegetation, smothered by a thick carpet of the twigs. The tendency of she-oaks to replace native species and become a monoculture makes the trees hated in Florida. But the trees are beloved in Australia where the carpet of twigs makes for a silent stroll through a forest of she-oaks. Well, almost silent. Even on still days, she-oaks whisper and sigh.
In 1896, Henry Lawson wrote a poem, Reedy River, about his wife, Mary, and their days along the banks of the river and strolling among the she-oaks. To read this beautiful poem, click on the link: http://members.ozemail.com.au/~natinfo/lawson/reedyriver.htm
(Compiled from: "Element Stewardship Abstract for Casuarina equisetifolia", Susan C. Elfers, The Nature Conservancy, 1988; "Casuarinaceae", K.L. Wilson and L.A.S. Johnson, Flora of Australia Online, Australian Biological Resources Study, Department of the Environment and Heritage, Australian Government, 2004; "Casuarinaceae R. Br.", Watson L., and Dallwitz, M.J., 1992 onwards, The Families of Flowering Plants: descriptions, illustrations, identification, and information retrieval. Version: 23 October 2005; Hortus Third, Staff L.H. Bailey Hortorium, NY State College of Agriculture and Life Sciences, Cornell University, Macmillan, NY, 1976; and "Casuarina", Wunderlin, R. P., and B. F. Hansen. 2004. Atlas of Florida Vascular Plants. [S. M. Landry and K. N. Campbell (application development), Florida Center for Community Design and Research.] Institute for Systematic Botany, University of South Florida, Tampa.)
