Regulation of Fruit and Seed Production in An Annual Legume, Cassia Fasciculata

This study examines the factors that limit female reproductive function (fruit and seed production) in the annual plant, Cassia fasciculata Michx. (Leguminosae), an hermaphroditic herb that inhabits prairies, open woods, and waste places in the eastern USA. Removal of competitors and addition of water to plants in the field showed that resource levels prior to fruit influence plant size which, in turn, is positively related to the number of fruit matured. Manual addition of pollen to flowers in the field did not increase the number of fruit matured, suggesting that fruit production was not pollinator limited. Removal of rapidly growing fruit resulted in growth and maturation of fruit that normally would not have matured, indicating that resources limited fruit production. In four populations studied, 24—70% of initiated fruit matured, 12—40% aborted or died, 3—31% were still developing at the time of plant death, and 61—12% were lost to predators. In fruit that matured, between 23% and 73% of initiated seeds reached maturity, 22—43% were aborted, and 0—49% were lost to seed predators. These data indicate that seed production was limited by resources and seed predators. It is hypothesized that overinitiation of fruit in C. fasciculata is an adaptive response to either; (1) the loss of juvenile fruits to seed predators, (2) variation in fruit quality coupled with the ability of the plant to selectively mature high—quality fruit, or (3) unpredictability of resource levels and survival during fruit filling. The generally low levels of predation on juvenile fruits make the first hypothesis unlikely for C. fasciculata. Plants did, however, selectively mature fruit with large numbers of developing seeds. Furthermore, variation in the number of fruit matured per inflorescence seemed to be related to variation in precipitation and plant survival through the fruit—filling period. Thus, the data support both the second and third hypotheses.