AGE AND SIZE STRUCTURE IN POPULATIONS OF A LONG-LIVED DIOECIOUS GEOPHYTE - BORDEREA PYRENAICA (DIOSCOREACEAE)

The age, size, and reproductive status were determined for plants in t hree populations of the dioecious Borderea pyrenaica, an endemic geoph yte of the Pyrenees. Age determination showed that this small alpine p lant spends at least 10-20 yr in the juvenile phase. The oldest plant was 305 yr old, which represents one of the longest life spans recorde d for any herbaceous plant. Simple mathematical models were fitted to describe survivorship curves. In general, the negative exponential fun ction described age structure better than the power function. Age and size distributions showed markedly different profiles in two of the th ree populations, indicating that the size structure cannot be used to infer the age structure of these populations. Female plants began flow ering at a larger size than males, whereas males were, on average, lar ger than females among old adults. Therefore, age structure will influ ence the relative size of adult male and female plants in a population .