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 barrel-cactus display dry garden garden-display garden-plants gravel ornamental pronounced-ribs protection ribbed ribbing rocks rocky soft-wooded-perennial thick-tough-skin