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The terms spine, prickle, and thorn have been variously used interchangeably in plant descriptions and cycads are no exception. It is clear from developmental studies and morphology that cycads do not have thorns, but rather have spines and prickles. Spines are present as reduced leaflets in species of Cycas, Dioon, Encephalartos, and Macrozamia, and none of these genera have prickles. In contrast, some species of Zamia and Ceratozamia have prickles, but none have spines. Lepidozamia, Bowenia, and Stangeria have neither spines nor prickles.
Keywords: prickle, spine, thorn
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Dennis William Stevenson holds a Ph.D. University of California, Davis 1975. He is Vice President for Laboratory Research at The New York Botanical Garden and Editor, Botanical Review. His expertise is in Cycads, Monocots, and Genomics. His major research interests in the past few years have focused upon the evolution and classification of the Cycadales (cycads) and their placement in seed plant phylogeny. He is conducting research on various facets of the biology of the Cycadales and Gnetales. These facets include reproductive biology, anatomy, cytology, molecular systematics, as well as taxonomic monographs and treatments of these groups for various floras being prepared for the neotropics. Another major research interest is the systematics of the monocots, particularly, the Commelinidae. The topics under investigation include developmental floral morphology, embryology, and inflorescence structure because this basic information is incomplete or unknown for many of these families. These data are being combined with gene sequence data to generate phylogenetic hypothesis on the origin and classification of the monocots. Dennis Wm. Stevenson's Author Page