Robust purpleblade split from its ancestor and colonized sandy sites, most notably beaches. The high silica content of these habitats allowed silicic acid present in adsorbed water to be deposited in vascular tissues with minimal cellular effort, significantly enhancing structural support and facilitating larger size. The silica deposits form microscopic fibers that overlap and connect vascular cells. The root system is fibrous and reaches as far as a meter below the surface to access water during dry periods. It may form moderately dense colonies that can stabilize sandy beaches.
Like its ancestor, the inflorescence grows from the apical meristem. This bears 3 reproductive appendages which have macrogamtetes that are fertilized by microgametes released from another individual's leaf tips. The inflorescence dies back and falls off at the last growth node to reveal a new apical meristem in the winter. The seeds are larger (1 cm diameter) and have thick, buoyant coatings that degrade after several months. This has had the consequence of allowing both ideal germination time (after the dry season) and the rare dispersal of seeds over water as far as Leopard Island in the east and Darwin in the west.