干旱区生态环境知识资源中心

Achenes (seeds) of the perennial shrub Launaea arborescens (Asteraceae) germinated under a wide range of environmental conditions. None of the seeds were dormant, nor was there any evidence that dormancy could be induced. Apparently, this semi-desert species has no means of preventing immediate germination. Achenes are produced and dispersed throughout the year, and we suggest that the timing of germination is regulated by the duration and degree of wetting and the presence of moderate soil temperatures. This germination behaviour suggests that there is no mechanism by which the germination of seeds formed one year can be delayed until subsequent years. By contrast, most desert plants accumulate persistent seed banks. The germination strategy of L. arborescens must be considered opportunistic, and we suggest that the survival of populations is ensured by other life history traits like continuous iteroparity and effective dispersal by wind. (C) 1997 Academic Press Limited.