The Australia Museum site provides the following information "Leaf-curling Spiders hoist a leaf from the ground and, using silk threads, curl it to form a protective cylinder, silked shut at the top and open at the hub.. They then sit in this cylinder with only their legs showing, feeling for the vibrations of a captured insect. The curled leaf protects them from birds and parasitic wasps. Sometimes other objects, such as snail shells (which come ready-curled), are used. In P. graeffei this leaf is suspended just above the centre of the web, but may be placed higher in other species. Juvenile spiders start off by bending over a small green leaf, but eventually graduate to larger dead leaves."
This spider has hoisted its leaf into a Blackthorn bush. The Blackthorns are in flower at the moment.