Trends in the evolution of dicotyledonous seeds based on character associations, with special reference to pachychalazy and recalcitrance

Abstract

VON TEICHMAN, I. & VAN WYK, A. E., 1991. Trends in the evolution of dicotyledonous seeds based on character associations, with special reference to pachychalazy and recalcitrance. The possible evolutionary status of the endothelium, hypostase, pachychalaza and the recalcitrant viability behaviour of seeds is considered in relation to bitegmy/unitegmy, crassinucellate/tenuinucellate ovules, nuclear/cellular endosperm development, large/small seed size, woody/herbaceous habit and tropical/temperate habitat. The presence of the endothelium, hypostase, pachychalaza and recalcitrance in dicotyledonous families is plotted against Dahlgren's system of classification. Results are compared with Sporne's advancement index for the various families. An endothelium is considered derived since it occurs more often in highly evolved superorders and is significantly associated with derived ovule and endosperm character states as well as with smaller seed size. A hypostase appears to be relatively ancestral and is significantly associated with pachychalazy and recalcitrance. The endothelium and hypostase have developed independently in many taxa and could be interpreted as being structurally and functionally analogous. Pachychalazy and recalcitrance are significantly associated with ancestral ovule character states and, at the species level, with large seed size (overgrown seed), woody habit and tropical habitat. The presence of pachychalazy, recalcitrance and associated large seed size are therefore regarded as ancestral character states of the dicotyledons. Consideration of currently accepted dicta on seed character state polarity, suggests a reversal in the evolutionary status of pachychalazy and large seed size.