ECOLOGY AND MORPHOLOGY OF BLOSSFELDIA-LILIPUTANA (CACTACEAE) - A POIKILOHYDRIC AND ALMOST ASTOMATE SUCCULENT

Plants of the monotypic Blossfeldia liliputana have the smallest bodie s 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 an d N Argentina. Based on observations and experiments in the field and in cultivation, morphology, anatomy, reproductive biology, certain asp ects of ecophysiology, and behaviour under water stress are described. The very small flowers are autogamous; the arillate hairy seeds are u nique within the family and represent a particular adaptation to ant d ispersal. These CAM-plants virtually lack stomata: 0.6 stomata/mm(2) r epresents 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 de gree of desiccation: under water stress the plants lose up to 80% of t heir weight within one year and can withstand an additional drought of at least another year. Thus Blossfeldia is poikilohydric like many li chens and mosses and represents the unique life form of a succulent re surrection plant.