arid barrel barrel cactus Cacti cactus clumps clusters coloring colors colouring colours compact covered echinocactus globose globular perennial pointed points pronounced ribs protective pups ribs round shape shaped sharp skin soft-wooded perennial spikes spination spines spiny surface symmetrical symmetry thick tough skin to-the-point cluster danger dangerous firm garden perspectives plants pronounced-ribs ribbing soft-wooded-perennial straight succulent surfaces thick tough upright barrel-cactus display dry garden-display garden-plants gravel ornamental protection ribbed rocks rocky thick-tough-skin