Plants Without Partners

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Published on: Jan. 2, 2001

Last revision: Nov. 8, 2010

Many Missouri families keep alive a tale of Grandad's walking stick. The story has many variations, but they basically all revolve around Grandad jamming his walking stick into the ground. The stick later sprouts into a living tree. Even Henry David Thoreau wrote of such an occurrence.

It sounds fanciful, but the tale may be factual. Lots of Missouri plants propagate by means of cloning.

Cloning has been in the news lately, but it's not really new. Cloning occurs naturally all of the time. It's a means of reproduction for many plants.

Essentially, cloning is reproduction without sex. Unlike sexually produced offspring, which have a blending of genes from both parents, Cloned offspring have the genes of only one parent, In fact, a clone is a genetic duplicate of its sole parent.

Nearly all Missouri plants that clone also reproduce sexually through flowers and seeds. Cloning, sometimes called vegetative reproduction, merely diversifies their reproductive capabilities.

If you've ever noticed a grove of sumac in the shape of a mound, you've seen the results of cloning. The oldest plants are in the center and are taller than those around them. The younger, shorter plants sprout from underground runners around the perimeter. Eventually, the runners wither away, leaving a completely independent sumac that is genetically identical to the sumac beside it.

Sassafras and gray dogwood are two common Missouri plants that also reproduce through this type of cloning. That is why you seldom see these plants growing alone. They're nearly always in small groves of genetically identical plants.

Many plants use underground runners to clone themselves. Several grasses use this method to spread through the soil. So do strawberries. A ring of May apples on a moist forest floor is a sign that cloning has been underway (and underfoot). May apple colonies can perpetuate this way for half a century if left undisturbed.

Blackberries, which have a three-year life cycle, have a different method of cloning. In the first year, the cane establishes itself. During its second year, the cane flowers and bears fruit, reproducing sexually. In the third year, the cane droops to the ground, giving blackberry brambles their characteristic, "bales-of-barbed-wire," look. When the drooping cane touches the ground, it can set roots for a new plant. Eventually, the original cane will dry up and break away, leaving a completely independent clone of the original plant. From there, the three-year cycle begins anew.

Black raspberries perform a similar cloning act, but they achieve it in only two years.

Many plants that grow from bulbs also reproduce through cloning. Tulips and daffodils have to be divided every few years because their bulbs have been busy cloning and crowding the soil. Irises, which grow from rhizomes, can also clone new plants. Perhaps the most ambitious cloner among these kinds of plants is the common orange daylily. When you walk in the woods and come across a patch of these, you've probably stumbled across an old homesite. Not only are the orange daylilies decorative, but their flowers, buds and roots are edible and may have supplemented the table fare of pioneer families.

Orange daylilies are also commonly seen growing in ditches beside roads and railroad tracks. They are originally from China and were brought to North America in the 19th century. They've clearly established themselves here, even though the orange daylily flowers are sterile. The plants can reproduce only by cloning. Most of the thousands of patches of orangedaylilies across Missouri are believed to be have been derived from one plant.

Duckweed is another common cloner. Duckweed is commonly found in Missouri ponds and slow streams. It is sometimes used in water reclamation projects because it can thrive in polluted water. In the wild, duckweed is fodder for ducks and provides shelter for many aquatic insects.

Though individual duckweed plants live only a few months, they can clone up to a dozen daughter plants in that time. Each daughter can clone at the same rate. Fortunately, this exponential growth potential is checked by hungry waterfowl and by Missouri's cold winters. However, there is a variety that can clone so quickly under perfect conditions that, if left unchecked, could theoretically cover the surface of the earth in only four months.

Because cloning produces exactly the same plant as the original, it is a useful tool for cultivating many species. Many ornamental plants and most trees bought at nurseries are clones that generally started from cuttings. An advantage of this is that a clone has a guaranteed performance. The clone of an especially productive apple tree will produce another especially productive apple tree under the same growing conditions.

A dwarf Japanese maple will consistently clone identical dwarf Japanese maples. For some plants, like cotoneaster, it is easier to clone than to grow a plant from a seed. Certain trees, like pecans, have been developed to be disease resistant, so clones of those strains will bear the same resistance. Azaleas will readily clone if their branches are allowed to touch the ground.

This genetic guarantee doesn't occur when plants are produced sexually, because both parents contribute genes to the offspring. Therefore, the offspring may contain some "wild card" genes.

African violets are probably the best known clone in American households. They grow easily from leaf cuttings, and since no new genes are added when the cutting sprouts, the result is a clone.

Cloning is relatively common among plants because plants are not ascomplicated as higher forms of life. Among insects, however, something close to cloning occurs regularly.

Bees are a good example. All of a hive's males, called drones, have no father. They develop from unfertilized eggs, so they receive no genetic contribution from a male parent. All of their genes come from the queen. Technically, this is not cloning because the drone is not a duplicate. It has only half of the queen's genetic constitution. Wasps, aphids and ants also use this close-to-cloning method in addition to sexual reproduction.

The propagation of the nine-banded armadillo can't be called true cloning, either, even though it results in genetic duplicates. Armadillos reproduce sexually, so the offspring have genetic contributions from both parents. Curiously, armadillos always produce litters of identical quadruplets, resulting in four genetically identical armadillos. They are clones of one another but not of either parent.

In Missouri, our champion cloner is the willow tree. Most commonly found along streams and around lakes, willow trees have brittle branches that snap off easily in the wind and litter the ground. High water carries the branches away and deposits them on muddy banks, where they take root and sprout new trees that are genetic duplicates of the parent. This readiness to clone has made willow ideal for streambank stabilization. Willow cuttings root and grow even if planted upside down.

In fact, grandad's walking stick, the one that magically sprouted into a tree, was probably cut from a willow branch.

"Clone" comes from the Greek word klon, meaning "twig." Many plants rely on cloning to reproduce, either exclusively or as a supplement to sexual reproduction. Each of the sumac plants in a grove is identical genetically, as are the plants in a May apple colony. Willow cuttings sprout quickly, making them ideal for planting to help stabilize eroding streambanks.

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