PATTERNS OF GENICULAR DEVELOPMENT IN AMPHIROA (CORALLINACEAE)

Two types of genicular development (designated Types I and II) are present in South African species of Amphiroa. Genicula of both types originate when medullary tissue near branch endings softens by decalcification. In Type I decalcification does not progress to the branch surface and the joint therefore does not become flexible until the cortex, which remains calcified, cracks and partly sloughs. This type occurs in all species of Amphiroa in South Africa except one, and possibly occurs in those in the rest of the world as well. In Type II decalcification continues centrifugally to the surface of the branch; this results in a geniculum comprising medullary and cortical tissue. As far as is known this type occurs only in Amphiroa ephedraea. Type I appears to be more primitive than Type II.