Plastic heteroblasty in beach groundsel (Senecio lautus)

Abstract

Senecio lautus (Asteraceae) is a heteroblastic herb that produces entire juvenile leaves and lobed adult leaves. Juveniles commonly grow from rock fissures where they are shaded and sheltered from high winds, whereas adult plants are exposed to high light and wind as they outgrow these refuges. Because the duration each plant is sheltered varies with the depth of rock fissures, I hypothesised that heteroblasty in S. lautus varies plastically in response to environmental conditions. I tested this hypothesis in a glasshouse experiment, which exposed developing plants to different light and wind conditions. Plants grown in windy conditions showed similar ontogenetic changes in leaf morphology to plants growing in a control treatment. However, the juvenile-adult transition was slowed in shaded conditions, indicating that heteroblasty in S. lautus varies plastically in response to light. Results were therefore consistent with the hypothesis that plastic heteroblasty is favoured in species that experience unpredictable environmental gradients during ontogeny. © 2005 Taylor & Francis Group, LLC.