DEVELOPMENTALLY VARIABLE,POLYMORPHIC WOODS IN CACTI

Sixteen genera of cacti were discovered to have polymorphic wood, that is, the plants produce one type of wood while young but a different type when older. The polymorphisms are: fibrous wood (with vessels and scanty paratracheal parenchyma) followed by parenchymatous wood (with vessels but few or no fibers) (Hylocereus venezuelensis, Dendrocereus nudiflorus, Borzicactus humboldtii, Haageocereus australis, Morawetzia sericata, Stephanocereus leucostele, Trichocereus schickendantzii); WBT wood (with wide-band tracheids, vessels, and apotracheal parenchyma but few or no fibers) followed by fibrous wood (Buiningia aurea, Oreocereus celsianus, Vatricania guentheri); WBT wood followed by parenchymatous wood (Echinopsis tubiflora, Gymnocalycium marsoneri, G. oenanthemum, Notocactus warasii, Parodia maassii); trimorphic wood in which WBT wood is followed by fibrous wood, which is followed by parenchymatous wood (Melocactus intortus, Arrojadoa braunii). The different phases within each plant may differ in vessel cluster size, percentage of the vessels that are solitary, diameter of vessels, and lignification of ray cells. Several of these genera are not closely related to the others, so wood polymorphism may have arisen several times.