Germiantion Requirements of the Desert Shrub Larrea Divaricata

Germination requirements of Larrea divaricata Cav. were studied in the laboratory using seed collected at 34 United States sites. Collection sites were grouped into three desert regions (Chihuahuan, Sonoran, Mojave) of increasing aridity from east to west. Optimum laboratory conditions for germination were: darkness, 23°C, leaching the mericarps with running water, wetting and drying cycles, exposure to cold temperatures prior to sowing, and maintaining the medium about the seeds near—zero in osmotic pressure and low in NaC1. Exposure of dry seeds to warm temperatures (37—71°C) prior to sowing resulted in marked reduction of germination. Maximum root growth was obtained at 29°C in a slightly acidic medium low in NaC1 and near—zero in osmotic pressure. There were no regional differences in germination behavior. Due to seed abortion, non—germination, and mortality over 6 months' growth, only 20 seedlings survive for every 100 mericarps sown under optimum conditions in the greenhouse. It is unlikely that large—scale germination and survival occur often in nature.