Ecological advantage of leaf heteroblasty in Costus pulverulentus (Costaceae)

Leaf heteroblasty is a plant phenomenon related to leaf development that describes substantial differences between temporally separated plant stages. This study explores the ecological advantage of leaf heteroblasty in the herb Costus pulverulentus C.Presl and analyzes its possible adaptive value. Heteroblasty was studied using leaf morphology analysis and characterizations of leaf area, specific leaf area (SLA), and leaf divergence angles along the crown. A light capture efficiency index (STAR) was also used by simulating plants with only top- or basal-leaf forms to test its adaptive value. Morphological analysis indicated that C. pulverulentus develop two leaf forms: basal leaves with an obovate form, and top leaves with an oblanceolate form. Mid-crown leaves showed a reduced SLA and angles of divergence, and an increased area compared with top and lower leaves, which may indicate greater space utilization for light acquisition. Plants with top-leaf forms showed greater STAR than plants with basal-leaf forms, likely due to lower self-shading and lower crown density produced by leaf arrangements. Results of this study suggests that changes in leaf size and morphology occur in later stages of plant development as an adaptation to reduce self-shading and crown density which promotes an adaptive advantage by increasing the STAR.