The Red Cluster Bottlebrush (Callistemon citrinus or Callistemon rigidus) is a hardy, fast-growing evergreen shrub, often trained as a small tree, known for its vibrant, crimson, brush-like flowers that bloom in spring and summer. Thriving in USDA zones 8-11, this 10-15 ft. tall, heat-tolerant plant attracts hummingbirds and butterflies, making it ideal for sunny screens, hedges, or focal points.