Spinescence in the New Zealand flora: parallels with Australia

Prickles, thorns and spines deter herbivory by large mammals. However, New Zealand lacked large mammals prehistorically and was instead home to large browsing birds. Perhaps as a result, very little research has been conducted on the production and function of prickles, thorns and spines in New Zealand plants. Here, I evaluate the ontogeny of spinescence in New Zealand and how it differs in taxa inhabiting offshore islands that never housed large browsing birds. I then review similar work on the ontogeny and biogeography of prickles, thorns and spines in Australia, where spinescence has been shown to deter herbivory by large vertebrates. Results show that a variety of New Zealand plant species deploy prickles, thorns and spines in similar ways to spinescent plants in Australia, suggesting that spinescence may have defended plants against large, avian herbivores. Results also highlight differences in the deployment of spinescence between the two floras, which may represent specific adaptations to avian browsers.