Australia is blessed by a very old ecosystem and a large biodiversity, especially in areas with “extreme conditions” caused by regularly occurring fires. To adjust to such harsh environments, plants have evolved various strategies. A particularly spectacular example is the seed storage and protection mechanism of the iconic Australian plant genus Banksia. Banksias can keep their seed on the plant for many years, building up a canopy stored seed bank. The delicate embryos are well protected in seed pods, consisting of dead, yet functional tissues. Foci of our research were the protection of the seeds during storage and fire exposure of the cones and their 2-step opening mechanism, which depends on a climatic gradient and requires location-dependent temperatures between 55 – 72°C for initial opening and subsequent exposure to water for seed release. Using materials science approaches we were able to identify, that the internal valve curvature of the pericarp acts as the “temperature sensor” for initial, temperature-triggered opening of the layered valves. Multiple layers prevent delamination of the endo- and mesocarp with their opposed cellulose orientation. A shape-memory effect of one of the layers stores energy after the first opening step for the second, water-fueled one, that leads to seed release. The experiments revealed how a dead material, such as the pericarp, can ensure longevity and delayed autonomous seed release upon a 2-step-trigger. Understanding the material properties and functionalities of these natural actuators does not only provide inspiration for biogenic material use but also impacts strategies of fire management with respect to biodiversity conservation.
