FLORAL VARIATION IN EICHHORNIA-PANICULATA (SPRENG) SOLMS (PONTEDERIACEAE) .2. EFFECTS OF DEVELOPMENT AND ENVIRONMENT ON THE FORMATION OF SELFING FLOWERS

Genotypes of the mid-styled morph of tristylous Eichhornia paniculata (Spreng.) Solms (Pontederiaceae) exhibit developmental instability in the position of short-level stamens under both field and glasshouse conditions. Elongation of one of the stamens to a position adjacent to the stigma results in automatic self-pollination of flowers. This modification initiates subsequent changes to floral morphology leading to the evolution of predominant self-fertilization in E. paniculata. The influence of genetic, developmental and environmental factors on the expression of stamen instability was investigated in experiments with genotypes from two populations from northeast Brazil and interpopulation hybrids. Genotypes from the three sources differed significantly in the degree and pattern of stamen instability expressed under uniform growing conditions. Significant position effects in the production of modified flowers were detected among genotypes using logistic regression techniques. Modified flowers were most frequently produced on later inflorescence branches in the flowering sequence and at proximal flower positions within an inflorescence branch. However, these patterns were complex, varying among genotypes and experimental conditions. Stamen modification increased in clones grown under water stress or at high temperature, demonstrating a significant environmental component to floral instability.