Fasciation

Fasciated CelosiaSome of the most popular new variations of recent plants are mutations that cause the stem and other plant parts to grow wide and flats. Also, shoots can appear to be composed of several fused parts, flattened, elongated or misshapen flower heads with numerous flowers. This is called fasciation.

Fasciation can occur in just about any kind of plant. Everything from weeds to trees will produce this unusual growth given the right circumstances. Gardeners who love oddball plants have propagated some of these rarities. Grafting or cutting propagation is the usual means by which horticulturists propagate fasciated plants. Fasciation is especially common in cacti and succulents, but willows, cockscomb and foxgloves also frequently show this abnormality.

This last summer I bought a beautiful, magenta, fascinated annual called Celosia argentea var. cristata (Cockscomb.) This annual plant carries its fasciation via seed, being a genetically mutated tetraploid plant (having four sets of chromosomes instead of two.)

Fasciated Cockscomb Celosia Cultivars

Photo credit: Susan Mahr, University of Wisconsin, Madison

The fasciated growth may be caused by a permanent change in the genome of the celosia, possibly triggered by a phytoplasma infection at some point in the distant past. If so, this is a case of natural genetic engineering. In some cases, seed-borne fasciation can be transmitted in the cell sap from the female parent to the offspring. The fasciated willow, Salix udensis ‘Sekka,’ is propagated from cuttings and used in exotic flower arrangements. This fasciated willow gives the bouquet a dramatic look with its wide, flat, reddish stems.

Fasciated Veronicastrum virginatum

Fasciated Veronicastrum virginatum

Plants commonly affected with fasciation include delphiniums, euphorbias, forsythia, foxgloves, lilies, Primulas and Veronicastrum. Ferns with fasciated tips often have names such as ‘monstrosa’ and ‘cristata’ and always look cool in the garden.

But what causes fasciation? Lots of things can cause the mutation to occur. It could be a random genetic mutation. In other cases, it can be induced by one or more environmental factors such as bacteria, fungi, virus, insects, frost and physical damage to the growing point caused by radiation or chemical mutagens. Even hoeing or forking around the plant has been implicated. But, in nature, fasciation has been attributed to infection from various disease agents or to insect infestation.

In some cases, as you may recall, plants rely on a growing point, called the apical meristem, to produce new growth. These meristematic cells eventually turn into leaves, stems and flowers. They are biologically flexible, but occasionally things go awry.

One of the replication errors that can occur as meristem cells divide is the production of fasciated or crested growth. In normal cases, plant meristems are dome-shaped and produce a cylindrical stem. But, in fasciated plants, the meristem and the stem itself flatten out and become elongated. It occurs as a mutation in a single cell that divides and creates other cells in the next zone of development. Then the mutated cells increase dramatically, and the growing point becomes the mature leaves and flowers. In this case, instead of making a round stem, the mutation causes a misfire in cell communication, and the flattened meristem happens.

Of the disease-causing agents, the most commonly associated pathogen is a relatively new group of organisms known as phytoplasmas. Retired Extension Horticulturist, Gerald Klingaman, explains that phytoplasmas represent an evolutionary midpoint between cellular pathogens, such as bacteria, and non-cellular viruses. Phytoplasmas lack a protective cell wall but have a cell membrane. They are difficult to see using conventional microscopy because, when viewed inside a plant cell, they appear as an amorphous blob. It is likely that the association of insects with fasciation is due to their role as a vector for these or other pathogens.

Fasciated asparagus

Fasciated asparagus

Fasciation can occur in just about any kind of plant. Everything from weeds to trees will produce this unusual growth given the right circumstances. Gardeners who love oddball plants have propagated some of these rarities. Grafting or cutting propagation is the usual means by which horticulturists propagate fasciated plants. Fasciation is especially common in cacti and succulents, but willows, cockscomb and foxgloves also frequently show this abnormality.

Fasciation itself is not usually contagious, that is, spreading through a planting. And, just because a particular plant exhibited fasciation one season, that does not necessarily mean it will again in the future. In most cases, it is just a random oddity. However, some plants, such as forsythia and Veronicastrum virginicum ‘Fascination’ do suffer repeat occurrences, perhaps indicating a genetic tendency to this mutation.

Wendy Lagozzino


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