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What Are Corms?
Corms (also called bulbo-tubers) are vertical underground stems that serve as a food storage organ for certain plant types, allowing them to survive cold winters and hot, dry summers. The exterior of a corm is covered in a tunic—a protective layer of papery skin. Each corm has at least one growing point at its top and roots that grow from its basal plate.
Corms also use the energy in their storage tissue to form new corms via vegetative reproduction. Before a corm dies at the end of the growing season, a new corm forms at the base of the mother corm's shoots. While this new corm develops, stolon stems emerge as offshoots and produce miniature corms, or cormels. As the plant continues to grow, the mother corm withers away completely and the new cormels become the main food storage organs for the next year's growth. Gardeners and farmers can divide small cormlets off from their parent plant to propagate clones of the plant.
6 Types of Plants That Produce Corms
For those interested in growing plants from corms, there are many popular plant options, including:
- Crocosmia: An evergreen or deciduous perennial native to southern and eastern Africa, this flowering member of the iris family produces sword-shaped foliage and exotic, vibrant blooms.
- Crocus: A flowering plant in the iris family that includes, crocuses are one of the earliest spring bloomers. The 90 different species of crocus have cup-shaped flowers that come in purple, yellow, cream, white, lavender, blue, and pink.
- Freesia: An herbaceous perennial flowering plant in the iris family, freesias are a popular cut flower due to their alluring fragrance and are available in shades of white, yellow, red, and lavender.
- Gladiolus: Gladiolus are a perennial flowering plant in the iris family. Also known as a sword lily, the gladiolus is known for its large blooms and three-foot-tall flower spikes.
- Liatris: Also known as blazing star, Liatris is an ornamental perennial with tall, spiky purplish-pink flowers. Its unique flowers bloom from the top down and attract butterflies and other pollinators.
- Taro: A tropical herbaceous plant of the genus Colocasia, the Taro is native to southeastern Asia and is grown primarily for its edible corms, which are a food staple in the Pacific Islands. Taro corms are consumed as cooked vegetables and also made into puddings, breads, and poi (a Hawaiian dish consisting of fermented taro corm that has been baked and pounded into a paste).
Corms, Bulbs, Rhizomes, and Tubers: What’s the Difference?
Geophytes are plants that store energy and water in underground organs, including corms, rhizomes, true bulbs, tubers, and tuberous roots. Each of these types of geophytes has its own unique characteristics:
- Corms: Corms are starchy, underground plant stems that preserve water, energy, and nutrients to enable the plant to reproduce and survive. They are solid (rather than layered), are covered in a paper-thin tunic, and grow vertically with a shoot at the top and roots emerging from the basal plate. Corms include crocuses, freesias, and taro.
- True bulbs: True bulbs are mostly round in shape and taper to a point at their top where flower stems sprout. Like corms, most true bulbs also have a tunic and grow roots from their bottom basal plate. True bulbs are similar to corms in appearance, but internally, true bulbs have layered fleshy scale rings (similar to an onion). Types of plants with true bulbs include: daffodils, hyacinths, amaryllises, snowdrops, tulips, and alliums.
- Rhizomes: Also known as a creeping rootstalk or rootstock, rhizomes are a main plant stem that grows horizontally underground or across the surface of the soil. This sideways growth pattern allows rhizomes to develop completely new root systems and sprout new shoots up from the surface of the ground. Types of plants with rhizomes include: the lilies of the valley, canna lilies, calla lilies, ginger, and asparagus. Learn more about rhizomes in our complete guide here.
- Tubers: Tubers, such as potatoes, are thick underground stems without a tunic or basal plate. Tubers contain many nodes or "eyes" that sprout buds on the tuber's surface. You can actually cut off any portion of a tuber with at least two buds, and it will grow into a genetically identical new plant. Types of plants with tubers include: potatoes, tuberous begonias, caladiums, anemones, yuca, Jerusalem artichokes, and cyclamens.
- Tuberous roots: Tuberous roots are modified, enlarged roots that store food for plants. They are typically clustered together at the bottom of a stem. Unlike tubers, which are covered in nodes, tuberous roots have one growing point on the proximal end. To propagate tuberous roots, separate the root into pieces that contain crown tissue from the proximal end. Types of plants with tuberous roots include: dahlias, daylilies, and sweet potatoes.
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