Anatomía del tallo y de la raíz de dos especies de Wilcoxia Britton & Rose (Cactaceae) del noreste de México

Stem and root anatomy of two Wilcoxia species distributed in the northeast of Mexico are studied to contribute to cacti knowledgement, to conclude about their rayless wood and to compare their anatomy with that of other Cactoideae members. Results show that Wilcoxia species have unistratified hypodermis, palisade chlorenchyma, lack of fibers in phloem, and rayless wood. Raylessness probably was an important factor in the evolution ofvascular cámbium in these species. Species differ in sorne quantitative characters and porosity type. In Wilcoxia's tuberous root, vascular tissue is scarse and restricted to radial rows, while storage tissue occurs in cortex and parenchyma associated to secondary xylem. Additional tuberous root developmental studies should contribute to understand anatomical diversity reported for Cactaceae.