Seasonal cleistogamy: a conditional strategy to provide reproductive assurance

Three populations of the cleistogamous species Oxalis acetosella and one population of the cleistogamous species Viola hirta (during 2 years), were investigated to determine whether the fertilization success of chasmogamous flowers influences the number of per ramet produced chasmogamous seeds, cleistogamous flowers, cleistogamous seeds and the total number of released seed per ramet. In both species chasmogamous (CH) flowers are produced before the cleistogamous (CL) ones. Fertilization success influenced number of produced CH seeds per ramet. In both species, ramets with one or more unfertilized CH flowers produced significantly fewer CH seeds. The number of produced CL flowers per ramet varied due to site membership (O. acetosella) and ramet size, but also due to the fertilization success of CH flowers. In both species, ramets with some CH flowers left unfertilized, responded with an increased production of CL flowers and seeds. In none of the species did the fertilization success of CH flowers influence the total seed output per ramet. Consequently, the increased production of CL flowers compensated for any loss in fruit- and seed-set owing to unsuccessful fertilization of CH flowers.