Resumen:
In Usnea aurantiaco-atra (Jaq.) Bory, growing in the Antarctica, a monthly variation in the usnic acid content, in individual thalli, was studied by means of scanning densitometry (HPTLC). The higher accumulation rates were quantified from January to May; there was a significant decrease in the concentrations from June to December, during the three years of study. In spite of the thalli were taken from a same location, variations could be observed in the usnic acid concentration in the individuals from within each monthly sample