Echium simplex, ein seltener Schopfrosettenbaum auf Teneriffa

Abstract

Echium simplex is one of three giant, monocarpic rosette trees among the 24 endemic species of the genus on the Canary Islands. The plant occurs with few populations at low elevation on the rocky north coast of the Anaga mountains on Tenerife. We studied the by far largest occurrence of E. simplex close to the lighthouse El Faro. The area was formerly agriculturally used, which is still indicated by the occurrence of weedy annuals and nutrient indicator plants. In a census of E. simplex in late April 2011, we counted c. 1300 flowering individuals, a total population size of about 10 000 individuals, and an average of 14.1% flowering individuals in three subsamples of the population. The size of flowering individuals was highly variable; even plants with rather small rosettes were flowering. Similarly, we estimated the age of flowering individuals to vary from 5 to 9 years. Largest individuals had rosettes with 90 cm in diameter and were up to 3 m high, with inflorescences of 1.5 m in height. The reproductive output is increasing exponentially with the size of plants and the length of their inflorescences; it amounted to more than 200 000 potential seeds in large individuals. We conclude that E. simplex despite its restricted occurrence in a small area is not endangered at the moment, but the plant deserves careful observation to allow immediate conservation measures in case of a decline in population size.