Yarb Tales - Roots
December 21, 2015

The Heritage Herb Garden at the Ozark Folk Center graces the park with visual colors and textures, sweet and pungent aromas. With their natural display, the herbs help us to interpret the history of the human use of plants.

After many decades of plant study, I finally found out why some plants will grow completely new leaves, flowers and vines from sections of roots. For a long while I thought that the underground fleshy growth made by bindweed, comfrey and horseradish should be called stems or rhizomes rather than roots.

I thought that propagation under normal garden and greenhouse conditions was limited to germinating seeds, stem cuttings and crown division. I had the incorrect idea that the only plants that could be propagated from underground parts were those that produced underground stems such as oregano and mint. The underground stems of these herbs are called stolons. The other underground stems are called tubers, bulbs, corms and rhizomes.

Stems move nutrients and water to and from leaves and flowers. They have nodes with growth buds from which new growth arises. Roots branch indiscriminately, have no nodes and produce root hairs to absorb water and nutrients.   

In my mind it followed that horseradish, comfrey and bindweed must reproduce from underground stems rather than roots. Any small pieces of rootlike appendages planted or left in damp soil will regenerate and form completely new plants. I even argued that horseradish condiment should not be called horseradish root!

I did know of the process called micropropagation, by which plant cells from most any plant part are cultured under laboratory conditions. The temperature, nutrient solution and hormone levels are artificially controlled to clone genetically identical plants. This sterile procedure enables the production of disease and pest free stock.

In botany, the word adventitious means plant parts that develop in unusual places such as roots that grow out of a stem after it is cut from a plant, or a leaf that develops roots, stems and flowers after it is removed from a plant. Sometimes this is in response to an injury. When a plant is pruned or broken, adventitious buds form on the stems below the cut from which new shoots emerge. The shoots differentiate according to what the plant needs for survival; roots or leaves and stems may develop.

It turns out that some plants have roots that will form adventitious buds that become stems, leaves and flowers. Because roots have no nodes, it seemed unlikely to me that differentiated plant tissue would be generated. Now I know that some roots are very good at adventitious growth.

In the business of herbs and in farming, it is advantageous that some plants like comfrey and horseradish produce adventitious buds which produce leaves because this is how the plants are propagated. Horseradish and comfrey plants produce no or very little viable seed.

It is a distinct disadvantage that bindweed asexually reproduces from adventitious root buds. This plant is listed as one of the top ten worst weeds in the United States because of this super power.

Now I start 2016 with an even deeper understanding of the mystery of plants to share. This work provides the gardener with the lifelong pursuit of knowledge. Merry Christmas, Happy New Year and best wishes to all.