HYGROCHASTIC CAPSULE DEHISCENCE IN NEW ZEALAND ALPINE VERONICA (PLANTAGINACEAE)

Premise of the study : Plant movement is more widespread than often recognized, involving different organs and mechanisms. Hygrochasy (opening in response to moisture) is a capsule-opening movement that is widely believed to be predominantly a feature of plants of desert and arid zones, where it may protect against seed predators and harsh climatic conditions and restrict dispersal to favorable germination times and sites. However, recently it has been reported from a wider range of environments. This study demonstrates that hygrochasy is much more common than previously realized, extending the phenomenon to plants of alpine habitats. Methods : Capsules of 23 species of New Zealand Veronica were collected, and we used light microscopy to investigate the anatomy and biomechanics responsible for the opening mechanism. Additionally, we collected morphological data to identify common traits of hygrochastic species. Key results : Hygrochastic capsule dehiscence was found in 10 alpine Veronica species. The opening mechanism is based on an antagonistic reaction between a nonlignified swelling tissue and a lignified resistance tissue. In Veronica, hygrochasy is associated with erect, narrowly angustiseptate capsules on short peduncles of creeping subshrubs or cushion plants. Conclusion : Hygrochasy is a common dehiscence type in New Zealand alpine Veronica, and for the first time, this mechanism is described in detail for plants in alpine habitats. We propose that hygrochasy provides an effective seed dispersal mechanism in solitary capsules embedded in cushion plants and may restrict dispersal within habitat patches.