Fasciation

Flattened, elongated shoots and flower heads that look like many stems compressed together are called fasciation. This strange-looking problem may be ugly or attractive, but is always interesting.

Fasciation on a delphinium. Credit: Tim Sandall/RHS The Garden.

Quick facts

Plants affectedAny plant, but usually only occasional
Main causes Variable: include micro-organisms & environmental factors
Timing Spring and summer

What is fasciation?

  • Fasciated stems are produced due to abnormal activity in the growing tip of the plant.  Often an abnormal number of flowers are produced on affected stems. Normal branches may arise from fasciated stems
  • Ring fasciation is where a ring of flowerheads are produced around a normal central flower, a phenomenon referred to as ‘hen and chicks’
  • Plants commonly affected include delphiniums, euphorbias, forsythia, foxgloves, lilies, primulas and Veronicastrum
  • Fasciation is unpredictable and is usually limited to a single stem. It seldom recurs the following year, although some plants, such as Forsythia and Veronicastrum virginicum ‘Fascination’ do suffer repeat occurrences, perhaps indicating a genetic tendency to this problem
  • Some fasciated plants are propagated to perpetuate their unusual forms. Ferns with fasciated tips often have names such as ‘monstrosa’ and ‘cristata’ and are highly collectable plants. The fasciated willow Salix udensis ‘Sekka’ is propagated from cuttings. Celosia argentea var. cristata carries its fasciation via seed, being a genetically mutated tetraploid plant (having four sets of chromosomes instead of two)

Symptoms of fasciation

  • Flattened shoots
  • Shoots that appear to be composed of several fused shoots
  • Flattened elongated or misshapen flower heads with numerous flowers

Causes of fasciation

Fasciation may be caused by:

  • Random genetic mutation or disruption
  • The bacterium Rhodococcus fascians
  • Viral infection
  • Damage to the plants by frost, animals (including insects), chemical or mechanical injury – even hoeing or forking around the plant have been implicated

Control

Affected parts of shrubs and trees can be pruned out if desired. Fasciation seldom recurs on herbaceous plants the following year.

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