Geographic Variation in Slash Pine

Mature cones and foliage were collected from each of 5 slash pine ( Pinus elliottii Engelm.) trees in 54 stands scattered throughout the species range, and 1-year-old progeny seedlings were grown. Twelve morphological traits were studied in cones, seeds, and foliage from the parents, and 13 morphological and physiological traits were studied in the seedlings. Most traits showed appreciable stand-to-stand variation. The patterns of stand variation differed among traits, but most were characterized by gradual changes between one or more "highs" or "lows." Many of the patterns contained a latitudinal gradient through Florida with a trend reversal in the "north-central" area (extreme south Georgia and north Florida). These patterns were believed to have resulted from adaptation to climatic or other environmental factors which change gradually through the species range. Some traits showed weakly defined or highly fluctuating gradients, suggesting some degree or randomness or discontinuity. A few showed distinctly clinal trends in the south and random variation in the north and a few showed strictly random variation. The two recognized varieties differed appreciably in several traits, but the results as a whole suggested that they are not discrete genetic entities, the patterns of variation usually being characterized by continuity.