THE PHOTOPERIODIC RESPONSE OF AMERICAN PROSOPIS AND ACACIA FROM A BROAD LATITUDINAL DISTRIBUTION

Prosopis and Acacia from North and South America were studied in the laboratory under constant and increasing night length under two temperature regimes. The Prosopis juliflora (Sw.) DC. complex showed strong populational differentiation; Acacia farnesiana (L.) Willd. showed minimal populational differentiation. In Prosopis a population from Oklahoma (36° N) showed the greatest inhibition of stem height under increasing night length. A population from Peru (6° S) showed least control of stem height by night length. In Acacia the response of the latitudinal series was relatively uniform within each of the 6 sets of light period-temperature conditions. In general the height increase for Acacia was two to three times greater under the warmer regime than under the cooler regime at a given night length. Since Acacia farnesiana occurs sympatrically with the Prosopis juliflora complex over a broad range of latitudes, it is of interest to find that the distributional mechanisms of these two leguminous trees are basically different.