araceae arum flower lilies nature petal pollen spathes stamen white yellow zantedeschia agricultural-pest arum-lilies arum-lily bush bushland calla-lily childsiana color colour death-lily declared-pest dense-clumps funeral-flower green-goddess herbaceous introduced invasive lifestock-threat lily-of-the-Nile out-of-control pasture-invader perennial pig-lily spreading St-Joseph's-lily surface surfaces surfacing texture textured textures thick-fleshy-leaf-blades toxic varkblom weed white-arum-lily zantedeschia-aethiopica