Complex sentence: They have leathery, strap-like leaves which arise from the base of the plant, sometimes from underground rhizomes and flowers which usually occur in clusters (sometimes singly) on stalks which emerge from the bases of the leaves.
Split into simpler sentences: They have leathery, strap-like leaves which arise from the base of the plant, sometimes from underground rhizomes. Flowers which usually occur in clusters (sometimes singly) on stalks which emerge from the bases of the leaves.