More than 4,000 species of plants belong to the lily family Liliaceae, but less than 100 species comprising the genus Lilium are commonly referred to as lilies. Occasionally plants in other genera and families, such as the water lilies belonging to the family Nymphaeaceae, are called lilies due to their resemblance to true lilies. Tall, erect stems, narrow leaves, and showy, six-part flowers are some of the most visible outward signs that a plant may be a lily, but true lilies can often be differentiated from other similar-looking specimens by their bulbs. The bulbs of true lilies are characteristically composed of loose scales that may be easily peeled apart. Each scale will eventually turn into a new bulb when planted, a method widely utilized by professional breeders of lilies.