The Strange Magic of Fasciation

Perhaps you have seen it in your garden — a plant stem that looks like a weird, flattened ribbon instead of a single cylinder, or the center of a daisy that looks like a stretched tube instead of a round button.

These are examples of fasciation, a term which comes from the Latin word "fascis," meaning band or bundle. Fasciation is the result of a disruption to the normal development of a growing point, or apical meristem, on a plant.

Something has caused that growing point to "go bonkers" (as my mother would say). The outcome is an apical meristem that is broad and laterally flattened, instead of having its usual domed shape. The most common effect of fasciation is a flattened stem, as if multiple stems are fused together, with an enlarged, fan-like crest at the stem tip. But it can also cause other weird and wildly contorted growth: stems may be coiled or bunched; leaves may be smaller, more numerous, and oddly angled; and flowers may be stretched, twinned, bunched, or distorted.

Fasciation can occur on any part of a plant, including the roots, but is most often seen affecting stems, flowers, or fruit. It has been observed (and photographed) on hundreds of different vascular plant species, from shrubs and trees to fruits and vegetables. But it seems to occur more frequently in certain plant families, including the cactus (Cactaceae), aster (Asteraceae), pea (Fabaceae), and rose (Rosaceae) families. Dandelions, rudbeckia, and coneflowers, all in the aster family, are common candidates for an occasional oddity in the garden.

Apical meristems, or growing points, on a plant are a kind of magical place from the get-go, even before anything strange happens. The meristem is a site of undifferentiated cells, akin to stem cells in the human body. As those cells actively divide and enlarge, they turn into the different kinds of cells you find in the structures you would expect to see at that location on the plant – whether that be root, stem, leaf, flower, or fruit.

With all that active growth, things are bound to go wrong once in a while. Various internal or external factors may damage cells in the growing tip, sometimes leading to the weird results of fasciation. Several possible triggers have been identified, including:

• Infection by some kind of virus, bacteria, or other microbe. One type of bacteria, Rhodococcus fascians, is known to cause fasciation as well as a disorder called "leafy gall disease." With these microscopic agents, the infection can be spread to other plants through contact or contamination.
• Random genetic mutations within the dividing cells.
• Attacks by insects, mites, or fungal growth.
• Exposure to chemicals or chemical imbalances within the cells. Some types of herbicides, which mimic the action of plant hormones within cells, can cause damage to growing plant tissue that resembles fasciation.
• Mechanical damage to the growing point.
• Environmental conditions, such as exposure to cold or frost.

Most of the time, the cause of the meristematic mistake is not apparent; it just seems to happen by chance — another unsolved mystery of nature. Apart from the microbial infection, none of these potential causes can spread the fasciation from one plant to another. Fasciation is not considered a disease, and it generally does not cause any lasting harm to the overall health of the plant. Occasionally, the fasciated plant tissue will revert to its normal growth pattern.

There is one more factor that may lead to fasciation, and that is genetic inheritance of the trait. There are certain genera and species of plants that can pass along the tendency in their genes. Fasciation can produce fascinating growth patterns, which many plant collectors and gardeners find beautiful and worth having. Through propagation, cultivated varieties (cultivars) have been developed, with names such as 'Cristata', 'Monstrosa', and 'Tortulosa', particularly within certain species of cactus and succulents that are popular with aficionados.

In the garden, cockscomb celosia, Celosia argentea var. cristata, is a common bedding annual with fasciated flowerheads; Allan Armitage calls them "colored brains." Another plant bred and grown for its fasciated stems is the Japanese fantail willow, Salix udensis 'Sekka'. Its reddish, twisted, flattened stems are used in flower arranging. Among edible garden crops, fasciation can result in the broad, lumpy shapes of beefsteak tomatoes and occasionally in large, deformed strawberries, sometimes called "cockscomb" strawberries. Nothing to be alarmed about, just more fruit to love….

Keep an eye out for the strange magic of fasciation in your own garden. You never know when it might show up to fascinate you.