Palm spines are restricted to certain taxonomic groups and so have systematic or diagnostic significance. But within this broad distinction there is great diversity in the kinds of spines that palms produce, these kinds then often having restricted distributions. In principle, however, spines are sclerotic, in order to maintain their rigidity, without regard to original anatomical features. Spines may have a superficial origin, or develop from internal tissues by breakdown of surrounding less resistant tissue; root-and rootlet-spines have internal origins because endogenous development is a root character. This chapter presents a synoptic key that provides a guide to palm spine morphology. It is followed by a listing of spine types in different taxonomic groups with some anatomical examples.
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