Raciation in Epacris impressa. III. Polymorphic populations

Abstract

Polymorphic populations occur throughout most of the distribution of E. impressa Labill., in which pink-flowered plants and white-flowered plants grow intermixed in the same locality. Measurements of corolla lengths indicate that these are panmictic populations: there is no difference between the mean lengths of pink and white corollas. In homogeneous populations (the vast majority) there is no seasonal variation in the flowering times of white-flowered bushes and pink-flowered bushes.

At Wilson's Promontory polymorphic scarlet/pink/white populations occur near polymorphic pinklwhite populations and monomorphic scarlet populations. Some of these triple polymorphic populations show heterogeneity of population structure, with seasonal differences of flowering time in the different morphs.

Polymorphic populations are generally intermediate between monomorphic populations of the different races of E. impressa. It is likely that they are of hybrid origin. The hypothesis that polymorphic populations form a base for disruptive selection into monomorphic populations is also discussed.