Bulbs, Corms, Rhizomes and Tubers

An onion is a true bulb, while a potato is a tuber. The inside of a corm has a texture more like the potato, not the onion.

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Many plants use underground parts known as bulbs, corms, rhizomes or tubers to store carbohydrates for use during difficult conditions. Plants that have an underground storage organ are called geophytes. Knowing the difference between them isn’t going to change your life, but I found it interesting and thought you might also.

True bulbs are made up of modified leaves. Think of an onion. The layers are leaves. The dried “skin” on the outside of the bulb is called a tunic. At the base of a true bulb is a root pad. New bulblets form off this root pad. Sego lilies, camas, tulips, daffodils and hyacinths all form bulbs.

Corms are similar to bulbs, but if cut in cross-section, they are solid like a potato and not segmented like an onion. That is because they are stems, not leaves. They also have a tunic and a basal root plate, but a main difference is that the corm always has at least one internode with a growing point. In the right conditions, this growing point initiates a stolon, or a lateral growing stem on or just beneath the surface. This stolon has growing points from which new plants can grow. They also form small corms, called cormels, around the root pad. In some species, these cormels replace the original corm each year. There are many examples of plants that use corms as part of their survival strategy. Glacier lilies, asparagus, bananas, wapatoo (arrowhead), Chinese water chestnuts and liatris to name a few, all form corms.

Rhizomes are continuously growing—underground or on surface—lateral stems that have growth points along their surface. New shoots can start from the top of these growth points and roots sprout from the bottom. This is one strategy for growth and plants that utilize it often form dense clusters. Bamboo, asparagus (which has corms and rhizomes), bearded iris, canna lilies, cattails, mint, turmeric and ginger are all examples of plants with rhizomatous habits. Johnson grass and Bermuda grass, two invasive weeds with an intent to take over the world, will accomplish their goals using their fast-growing rhizomes.

Tubers are also underground stems, but are not at the base of the above ground portion. They are referred to as stem tubers and form from thickened rhizomes or stolons.  There is often more than one tuber per plant. Bulbs, corms, and rhizomes produce an offspring while tubers grow in size every year. However, tubers form “eyes” that can sprout and provide asexual reproduction. Tubers on the noxious weed, white byrony, a smothering vine, can become as large as basketballs. Digging out these mega tubers is the only way to kill this plant. Potatoes, yams, begonias and anemones are all examples of plants with tubers.

There is another type of tuber that forms from roots rather than stems and is called a root tuber. In order for asexual reproduction to occur, a piece of a root tuber must include part of the crown of the plant—there are no nodes, buds or growth points. If you ever wondered what the difference between yams and sweet potatoes is, now you know. Sweet potatoes, dahlias and day lilies all produce root, not stem, tubers.

Finally, while asexual reproduction is very common among geophytes, these plants still produce seed and can be started from seed. It may take three years to get a tulip to blossom stage when planted by seed, but this can be a far less costly method of getting started.

These underground “storage units” really give geophytes an edge when conditions get tough. Keeping a food reserve might be smart business for humans too.

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Help Idaho Wildlife

When we traveled across the state in October 2017, most of the vehicles we saw using the wildlife management areas did not have wildlife plates. Buying wildlife plates is a great way for non-hunters and hunters alike to support wildlife-based recreation like birding.

C'mon folks, let's help Idaho's wildlife by proudly buying and displaying a wildlife license plate on each of our vehicles! 

See below for information on Idaho plates. Most states have wildlife plates so if you live outside Idaho, check with your state's wildlife department or vehicle licensing division for availability of state wildlife plates where you live. 

And tell them that you heard about it from Nature-track.com!

Wildlife License Plates

Great news! as of 2024, there are three NEW designs for license plates. They still are bluebird, cutthroat trout and elk, but they are beautiful.

Idaho Wildlife license plates provide essential funding that benefits the great diversity of native plants and wildlife that are not hunted, fished or trapped—over 10,000 species or 98% of Idaho’s species diversity. Game species that share the same habitats (such as elk, deer, antelope, sage-grouse, salmon, trout) also benefit from these specialty plates.

No state tax dollars are provided for wildlife diversity, conservation education and recreation programs. Neither are any revenues from the sale of hunting or fishing licenses spent on nongame species. Instead, these species depend on direct donations, federal grants, fundraising initiatives—and the Idaho Wildlife license plates.

Both my vehicles have Bluebird Plates. I prefer the bluebird because the nongame program gets 70 percent of the money from bluebird plates, but only 60 percent of the money from elk and trout plates - 10 percent of the money from elk plates supports wildlife disease monitoring and testing programs (to benefit the livestock industry) and 10 percent from cutthroat plates supports non-motorized boat access.

Incidentally, in 2014, the Idaho Legislature denied the Department of Fish and Game the ability to add new plates or even to change the name of the elk and cutthroat plates (very specific) to wildlife and fish plates, a move that would have allowed for changing images occasionally and generating more revenue. It would seem that they believe that we Idahoans don't want a well funded wildlife program.

I think it is time we let the Legislature know that Idahoan support wildlife funding and that we would like to see these generic plates come to fruition.