Observations of inflorescence patterns and flower sex in a population of Sagittaria papillosa Buch. (Alismataceae)

Sagittaria papillosa Buch. is monoecious with unisexual flowers, pistillate below, staminate above, typically with an unbranched scape. A large population with unusual numbers of staminate and bisexual flowers on the lowest whorl of the inflorescence and many particles was quantitatively evaluated. First-formed inflorescences had more staminate and bisexual flowers than those produced later. Branched scapes were predominantly found to be the second inflorescence produced by a given plant. Genetic crosses between flowers on recemes and panicles produced no branched inflorescences. When grown under greenhouse conditions all tested plants had racemes with pistillate flowers in the lower whorls and staminate ones above. Data from soil parameters, daylengths and air temperatures are compared to reported information on modification of flower sexuality by these factors.