Ecology and morphology of Blossfeldia liliputana (Cactaceae): A poikilohydric and almost astomate succulent

Plants of the monotypic Blossfeldia liliputana have the smallest bodies of all Cactaceae. The button-like plants with a diameter of usually some 10 mm occur in rock crevices in arid regions between S Bolivia and N Argentina. Based on observations and experiments in the field and in cultivation, morphology, anatomy, reproductive biology, certain aspects of ecophysiology, and behaviour under water stress are described. The very small flowers are autogamous; the arillate hairy seeds are unique within the family and represent a particular adaptation to ant dispersal. These CAM-plants virtually lack stomata: 0.6 stomata/mm(2) represents the lowest number in terrestrial autotrophic vascular plants. However, all other xeromorphic features characteristic for globular cacti are absent (e.g. no thickened cuticle, no thickended outer cell walls, no thickened hypodermal layers). These features allow a high degree of desiccation: under water stress the plants lose up to 80% of their weight within one year and can withstand an additional drought of at least another year. Thus Blossfeldia is poikilohydric like many lichens and mosses and represents the unique life form of a succulent resurrection plant.