The protected valleys and alluvial flats found along streams and creeks provide ideal growing conditions for the coast redwood, with many trees exceeding 300 feet (100 meters) in height. Other trees include hardwoods such as tanoak (Lithocarpus densiflorus), madrone (Arbutus menziesii), big-leaf maple (Acer macrophyllum), California bay or laurel (Umbellularia californica), and red alder (Alnus rubra). Sword fern (Polystichum munitum) and redwood sorrel (Oxalis oregana) are the most common members of redwoods' understory, and are accompanied by rhododendron (Rhododendron macrophyllum), huckleberry (Vaccinium spp. ), salal (Gaultheria shallon), azalea (Rhododendron occidentale), and other shrubs.