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Germination Patterns of Dimorphic Achenes in Three Related Species of Scorzoneroides (Asteraceae, Lactuceae) Growing in Different Environments

Scorzoneroides palisiae, S. salzmannii, and S. muelleri (Asteraceae) are phylogenetically close annuals with dimorphic achenes. Although these three species are characteristic to areas with some degree of disturbance, S. palisiae and S. salzmannii grow in Mediterranean environments, whereas S. muelleri preferentially grows in semi-arid environments. This study compared the germination characteristics of central and peripheral achenes subjected to different storage times. Both central and peripheral achenes of the three Scorzoneroides species were completely dormant immediately after dispersal. This dormancy was reduced after six months in dry storage, and practically disappeared after more than a year in storage. Six-month central achenes of S. palisiae and S. salzmannii displayed lower dormancy levels than peripheral achenes did, producing a mixed germination pattern. However, 6-month central achenes of S. muelleri displayed the same dormancy levels as those of peripheral achenes. Furthermore, there was a nearly significant negative correlation among germination and the annual aridity index in the studied populations. We suggest that this increase in dormancy may be interpreted as an adaptation to semi-arid ecosystems.