Studies on the Autecology and Population Biology of the Monocarpic Perennial Grindelia lanceolata

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Abstract
G. lanceolata (Compositae) grows in open habitats in shallow, rocky soils developed over limestones. Some freshly matured achenes from both disc and ray flowers can germinate in light, but disc achenes germinate over a wider range of temperatures than ray achenes. Stratification lowers the temperature requirement for germination and partially substitutes for the light requirement in both types of achenes. When stratified and incubated in darkness, disc achenes germinated better than ray achenes at all temperatures. In the field some germination occurs in autumn, but most of it occurs in early spring. High seedling mortality occurs during the 1st growing season and less than 1% of the plants that germinate flower and produce seeds. After germination, a rosette of leaves is produced and the plants grow from 2-4 yr before flowering. There are many more nonflowering than flowering plants in the populations and both groups of plants are composed of individuals of various ages. Vernalization is an absolute requirement for flowering and vernalized plants flower under both long and short days. GA3 did not substitute for the chilling requirement for flowering. The reserve stage in the life cycle is the rosette stage; rosettes grow slowly, taking advantage of favorable periods for plant growth until they reach the proper size to be vernalized. Lack of an effective means of achene dispersal, inability to maintain reserves of achenes in the soil and low competitive ability of rosettes prevent the species from growing in intermittently disturbed habitats occupied by weedy species of monocarpic perennials.