Pitayos ('<'I'>'Stenocereus'<'/I'>' spp.) are columnar cacti that produces edible fruit under both wild and cultivated conditions. Until recently the study of pitayos has been relatively neglected even though they have been a crucial staple for the inhabitants of subtropical semiarid lands of Mexico since ancient times. The main objective of this work is to relate seasonal aspects of vegetative and reproductive growth, CO'<'SUB'>'2'<'/SUB'>' uptake, and carbohydrates resources to abiotic components of the environment. Flower and fruit production occur during the dry season in theand this century late winter and spring, roots grow during the summer wet season, and stem elongation commences in the autumn at the beginning of the dry season. Vegetative growth thus does not coincide with reproductive growth, as it does for other fruit crops in temperate and tropical regions. The time offset of vegetative and reproductive activities reduce competitive sink effects, regulating assimilate partition to different organs, which may allow '<'I'>'Stenocereus queretaroensis'<'/I'>' to adapt to water limited environments. Reserve carbohydrates (starch, mucilage) accumulate early summer just after reproductive growth and in the early winter just after stem extension. Reducing sugar increase during the middle of the summer before stem extension. The low rates of growth and photosynthesis for '<'I'>'S. queretaroensis'<'/I'>' are associated with low tissue levels of nitrogen, chlorophyll and some micronutrients (Fe, Mn). Low levels of gibberellic acid may also contribute of its slow growth rate. It does not respond morhologicallly to irrigation during the dry period, indicating a low plasticity for growth. Although '<'I'>'S. queretaroensis'<'/I'>' is cultivated its physiological and phenological activities closely resemble those of wild CAM species and other wild perennial plants, reflecting its rather recent domestication and the fact that selections were based mainly on fruit quality and adaptation to aridity rather than biomass partition.

Key words: Adaptation,aridity,cacti,carbohydrates,growth,photosynthesis