Giant Rhubarb. Gunnera is a very robust herbaceous perennial, forming a spreading clump of lobed, rounded, rough- textured leaves with spiny stems 1-2m in width. Tiny red - brown flowers are borne in erect panicles to 1m height. Deciduous clump forming. Grow in permanently moist, humus - rich soil in full sun or partial shade. Protect crown by mulching during the winter mouths. Pot Size 1lt.