Seed germination in Launaea arborescens : a continuously flowering semi-desert shrub Wolfgang Sch ¨ utz* & Per Milberg†‡ *Institut f¨ ur Wasserwirtschaft und Landschafts¨ okologie, Christian A lbrechts Universit¨ at Kiel, Olshausenstrasse 40, D-24098 Kiel, Germany †Department of Crop Production Science, Swedish University of Agricultural Sciences, Box 7043, S-750 07 Uppsala, Sweden ( Received 1 February 1996, accepted 30 April 1996) 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 tem- peratures. 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. ©1997 Academic Press Limited Keywords: Launaea arborescens ; germination; seed dormancy; continuous iteroparity; Asteraceae Introduction Continuous iteroparity, i.e. when flowering occurs throughout the year, is a widespread plant trait in humid tropical regions (e.g. Knapp, 1973). In seasonal environments, however, where water availability or temperature restricts the length or timing of the growth period, it is a much rarer phenomenon. For example, in the Province of Almeria in SE Spain, only 1·3% of the native and naturalized flora for which data on flower phenology (2470 taxa) are available can be found flowering throughout the year (Sagredo, 1987). Many of these species are short-lived ruderals, and nine species are dwarf-shrubs or shrubs. One consequence of such a life history is that seeds are dispersed, or available for ‡ Present address: School of Environmental Biology, Curtin University of Technology, GPO Box U1987, Perth WA 6001, Australia. Journal of Arid Environments (1997) 36: 113–122 0140–1963/97/010113 + 10 $25.00/0/ae960201 © 1997 Academic Press Limited