Bulbs are marvelous organisms. Only a few of the flowers we think of as coming from bulbs are actually “true” bulbs; the diverse family known as “flowering bulbs” includes corms, tubers and rhizomes. Within that diversity lie the keys to the flowers' identification. Inside, they all shelter the embryo of a plant and food for its growth. Unlike seeds, which contain only enough nutrients to get a plant started, bulbs contain enough nutrients for an entire season’s growth and flowering.
Separate the true bulbs. True bulbs are rounded on the bottom with a “basal plate” out of which grow the plant’s roots. True bulbs have a pointed top where the stem of the plant will grow. True bulbs may be tunicate bulbs (tulips and daffodils, allium) which are covered by a papery “tunic” or scaly bulbs (lilies) which have no tunic; both types grow scales each year from the bottom “basal plate”.
Look for smaller bulbs with indented bottoms and flat or pointed tops that are either covered with a tunic or have a rough surface; these are corms. Most of their food is located around the base which holds the stem tissue. Gladioli, freesia, crocus, wand flowers and Tritonia (blazing star) all grow from corms. Corms that are lifted in the fall must have the current year’s dead stem section removed from the bottom to allow new roots to form next season.
Find bulbs that look like big flat corms with several buds on top. Tubers are often softer than true bulbs or corms. Some types of begonia and oxalis as well as the vining gloriosa lily (vine) grow from tubers. Some perennials, notably anemones and dahlias, grow from roots that mimic the tuber in appearance but which are not part of the stem; “tuberous roots” can be separated from the stem to make new plants.
Identify bulbous rhizomes by their long shapes with lateral buds which turn up to grow into lily of the valley, cannas and some iris species. These rhizomes grow in annual layers and contain a year’s worth of food like other bulbs but look like fat, homely roots. “Rhizomous roots” like those of peonies and daylilies are not bulbs.
Compare size and methods of propagation. Lily bulbs grow up to 6 inches or more in size but anemone tubers are so small that they look like flakes of bark. Tunicate bulbs grow large and propagate bulblets that grow alongside the basal plate. Scaly bulbs grow bulblets around the basal plate and self-propagate along the part of the stem that grows under the soil surface. Tubers and rhizomes often rot in the center or along their length; they must break into pieces, each of which must contain live buds in order to succeed.