INFLUENCE OF PLANT SIZE AND CLIMATIC VARIABILITY ON THE FLORAL BIOLOGY OF FOUQUIERIA SPLENDENS (OCOTILLO)

Abstract

The floral biology of Fouquieria splendens (Fouquieriaceae), a drought-deciduous shrub with wandlike branches, was studied in the northern Sonoran Desert. Two different measures of plant size, number of branches long enough to flower (>1 m in length) and actual number of reproductive branches, were used to examine the effect of plant size on reproductive output and floral display. Number of flowers and fruits increased with either measure of plant size. Annual flower production ranged from 190 to 6465 per plant and averaged 2553. Annual fruit production ranged from 9 to 1760 per plant and averaged 390. Because some branches long enough to flower did not do so, number of reproductive branches was a stronger predictor of flower production than number of branches > 1 m long. Inflorescence size (mean number of flowers per panicle) was not significantly related to plant size (number of flowering branches) in 2002 or 2003; in fact, the range in inflorescence size on certain individual plants was about as wide as the range for the entire sample. Interannual variation in floral parameters was examined by monitoring the same set of branches in two years, one unusually dry, one with nearly normal rain. In 2002, the dry year, panicles were numerous and sparsely flowered; in 2003, the wetter year, panicles were relatively few and much more densely flowered. Although flowers appeared normally abundant in the wetter year, mean number of flowers per branch was in fact 39% lower than in the dry year. Percent fruit set per panicle in 2003 (36%) was more than twice that in 2002 (16%). Even so, average number of fruits per branch did not differ between 2002 and 2003. Evidently flower production on a per-branch basis was high enough in 2002 to compensate for poor fruit set in that year, resulting in about as many fruits as in 2003.