GREENHOUSE AND LABORATORY STUDIES ON THE ECOLOGICAL LIFE-CYCLE OF DALEA-FOLIOSA (FABACEAE), A FEDERAL ENDANGERED SPECIES

Certain aspects of the seed and flowering stages of the ecological lif e cycle of the endangered species Dalea foliosa (Gray) Barneby were in vestigated under greenhouse and laboratory conditions. Seed dormancy i n this species is due to a water-impermeable (''hard'') seed coat that can be broken completely by mechanical scarification. Nondormant seed s germinated over a wide range of temperatures in both light and darkn ess. Soaking in concentrated sulfuric acid for 5 min, dry-heating at 8 0-100 degrees C for 25-80 min, and dipping in boiling water for 1 min broke dormancy in 52%, 50-77%, and 29%, respectively, of the seeds. Fi re caused breakdown of the hard seed coat of seeds on the soil surface , but killed the seeds. Dormancy was not broken by freezing and thawin g, soaking in absolute ethanol, or exposing seeds to simulated-summer followed by winter-stratifying temperatures. Seeds sown in a nonheated greenhouse and those in soil samples collected at a population site g erminated over a several-year period, mostly in March and April. Thus, the species can form a persistent seed bank. No plants of D. foliosa flowered under a 10-h daily photoperiod (short day), whereas 100% of t hose given an 8-h photoperiod plus a 2-h night interruption (long day) flowered. One-hundred percent of the plants kept in a heated greenhou se all winter and 100% of those exposed to winter cold in a nonheated greenhouse flowered. Thus, D. foliosa is an obligate long-day plant th at does not require exposure to low temperatures for bud break, shoot growth, or flowering. Management implications of this study are discus sed.