FACTORS AFFECTING REPRODUCTIVE SUCCESS IN A RARE GRASS, CALAMAGROSTIS-PORTERI SUBSP INSPERATA

Calamagrostis porteri A. Gray subsp. insperata (Swallen) C. W. Greene is a rare grass that is currently treated as a ''species of concern'' by the U.S. Fish and Wildlife Service. Production of viable seed had n ever bren observed, and little was known about the factors affecting t his reproductive failure. In this study we examined the effects of mat ernal genotype, pollen source, and light intensity on caryopsis (the s ingle-seeded fruit produced in grasses) production. Maternal genotype and pollen source (self vs. outcross) significantly affected the numbe r of caryopses initiated, while light intensity had no significant eff ect. However, nearly all of the caryopses initiated aborted late in de velopment. In the 2000+ florets we examined. only one fully filled, vi able caryopsis was found. The conditions under which this caryopsis wa s produced suggest future courses of management.