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