Marissa Jernegan
Physaria ludoviciana (Nutt.) O’Kane & Al-Shehbaz (silvery bladderpod; Brassicaceae), formerly Lesquerella ludoviciana, is state endangered in Illinois and Minnesota sand prairies. An overview of how seed biology affects its ability to persist is lacking. Our goal was to evaluate how seed biology (production, afterripening, longevity and seedling establishment) affects the persistence of Physaria ludoviciana. Fruits were collected in Mason County, Illinois in June of 1999-2002 and 2007. Inflorescence structures were counted to estimate seed production. Fruits from lower and upper portions of the inflorescence were separated before removing seeds since seeds on lower portions of stalks mature before those on upper portions. Reproductive plant densities were 1-4 plants/m2 with ~500 seeds per plant. Seeds were germinated in Petri dishes with moistened filter paper at 25°C with continuous light. Seed vigor was affected more by maturity than date or year of collection. Seeds collected in 2007 were germinated at two month intervals after harvest to determine whether afterripening occurred. In these trials, germination rates increased greatly when seeds were stored for six months compared to seeds without any storage. In other years, seeds stored at 4ºC with 40-50% relative humidity remained viable for at least 7.5 years. Although no seeds were found in soil cores, seedlings still managed to establish as seedling densities ranged from 1-11 seedlings/m2 during surveys in June 2000, 2002, and 2007. These studies in seed biology allow us to predict the recruitment of P. ludoviciana and could be useful in restoration and land management efforts.
Keywords: BRASSICACEAE, PHYSARIA, LESQUERELLA, ENDANGERED, SEED BIOLOGY
