Vegetative architecture of Elaeocarpus hookerianus. Periodic growth patterns in divaricating juveniles

Abstract

Elaeocarpus hookerianus Raoul, a canopy tree native to New Zealand, has a divaricating juvenile stage. The juvenile produces short shoots on both vertical and horizontal axes in the spring; long shoots are formed and expand most in summer months. Axes have regions of long internodes interspersed with regions of short internodes. Long internodes are associated with production of sinuate, linear-lanceolate leaves, the outgrowth of many lateral branches, and a wide angle of divergence between terminal and lateral axes. Regions with short internodes bear smaller, obovate leaves, and lateral outgrowth is suppressed. Periodicity in internode length is synchronous for first- and second-order horizontal axes at comparable distances along a branch. Vertical axes elongate more extensively, bear more linear lanceolate leaves, and branch more prolifically than horizontal axes. Topological growth, as determined by monthly estimates of mean order and of partition asymmetry, is similar for vertical and horizontal axes; both become more symmetrical towards the end of the season. Most leaves fall, and growth halts over winter months. The characteristic habit of juvenile E. hookerianus results from weak apical control of lateral shoot outgrowth, and periodic growth that provides for efficiency in light capture and expenditure for structural support. Vertical axes are considered to 'explore' the environment peripheral to the plant's canopy, whereas horizontal axes 'exploit' the canopy volume already captured.