Casuarina is a genus of flowering plants in the family Casuarinaceae, and is native to Australia, the Indian subcontinent, Southeast Asia, islands of the western Pacific Ocean, and eastern Africa. Plants in the genus Casuarina are monoecious or dioecious trees with green, pendulous, photosynthetic branchlets, the leaves reduced to small scales arranged in whorls around the branchlets, the male and female flowers arranged in separate spikes, the fruit a cone containing grey or yellowish-brown winged seeds.
Plants in the genus Casuarina are dioecious trees (apart from C. equisetifolia that is monoecious), with fissured or scaly greyish-brown to black bark. They have soft, pendulous, green, photosynthetic branchlets, the leaves reduced to scale-like leaves arranged in whorls of 5 to 20 around the branchlets. The branchlets are segmented at each whorl with deep furrows that conceal the stomates. Male flowers are arranged along branchlets in spikes with persistent bracteoles, female flowers in spikes on short side-branches (effectively "peduncles") that differ in appearance from vegetative branchlets. After fertilisation, the female spikes develop into "cones" with thin, woody bracteoles that extend well beyond the cone body. The cones enclose grey or yellowish-brown winged seed known as samaras.[3][4][5][6][7][8]
The genus Casuarina was first formally described in 1759 by Carl Linnaeus in Amoenitates Academicae and the first species he described (the type species) was Casuarina equisetifolia.[2][9] The generic name is derived from the Malay word for the cassowary, kasuari, alluding to the similarities between the bird's feathers and the plant's foliage.[10]
The following is a list of Casuarina species accepted by Plants of the World Online as of April 2023:[11]
In 1982, Lawrence Johnson raised the genera Allocasuarina and Gymnostoma in the Journal of the Adelaide Botanic Gardens, and transferred some species previously included in Casuarina to the new genera. The species of Allocasuarina previously in Casuarina are: A. acuaria, A. acutivalvis, A. campestris, A. corniculata, A. decaisneana, A. decussata, A. dielsiana, A. distyla, A. drummondiana, A. drummondiana, A. fraseriana, A. grevilleoides, A. helmsii, A. huegeliana, A. humilis, A. inophloia, A. lehmanniana subsp. lehmanniana, A. littoralis, A. luehmannii, A. microstachya, A. monilifera, A. muelleriana, A. nana, A. paludosa, A. paradoxa, A. pinaster, A. pusilla, A. ramosissima, A. rigida, A. robusta, A. striata, A. tessellata, A. thuyoides, A. torulosa, A. trichodon and A. verticillata. The species of Gymnostoma previously included in Casuarina are G. chamaecyparis, G. deplancheanum, G. intermedium, G. leucodon, G. nobile, G. nodiflorum, G. papuanum, G. poissonianum, G. rumphianum and G. sumatranum and G. webbianum.[12]
C. cunninghamiana, C. glauca and C. equisetifolia have become naturalized in many countries, including Argentina, Bermuda, Cayman Islands, Cuba, China, Egypt, Israel, Iraq, Mauritius, Kenya, Mexico, Brazil, South Africa, the Bahamas,[13] and Uruguay. They are considered an invasive species[14][15] in the United States, especially in southern Florida[16] where they have nearly quadrupled in number between 1993 and 2005 and are called the Australian pine.[17] C. equisetifolia is widespread in the Hawaiian Islands where it grows both on the seashore in dry, salty, calcareous soils and up in the mountains in high rainfall areas on volcanic soils. It is also an invasive plant in Bermuda, where it was introduced to replace the Juniperus bermudiana windbreaks killed by a scale insect in the 1940s.[18]
Fruit of C. equisetifolia Casuarina is a genus of flowering plants in the family Casuarinaceae, and is native to Australia, the Indian subcontinent, Southeast Asia, islands of the western Pacific Ocean, and eastern Africa. Plants in the genus Casuarina are monoecious or dioecious trees with green, pendulous, photosynthetic branchlets, the leaves reduced to small scales arranged in whorls around the branchlets, the male and female flowers arranged in separate spikes, the fruit a cone containing grey or yellowish-brown winged seeds.
