Symptoms
Stems and flowerheads looks very odd. The stem is distorted, flattened and ribbed, and the flowers are small and ill-formed.
Cause
Fasciation is a condition that may randomly
affect a diverse range of plants. Round stems are flattened,
suggesting many stems have fused together. True fasciation
is the product of a single, normally dome-shaped growing point
that has become abnormally broadened and flattened. Any sideshoots usually remain small and undeveloped.
The condition may be caused by random genetic disruption
or infection by the bacterium that causes leafy gall disease (Rhodococcus fascians).
It can also be initiated chemically or mechanically by, for
example, frost action, insects, or damage by chance when hoeing
or forking.
Plants commonly affected: delphiniums (above), euphorbias, forsythia (left), foxgloves, lilies, primulas.
Control
None. Fasciation is unpredictable and usually limited to a single stem. It seldom recurs the following year, although some plants, such as Forsythia and Veronicastrum virginicum ‘Fascination’ do suffer recurrences, perhaps indicating a genetic tendency in some species and cultivars.
Can I perpetuate fasciation?
In some woody plants, such as Cryptomeria
japonica 'Cristata' (right) and Salix udensis
'Sekka', it is an established characteristic and can be perpetuated
by cuttings. Celosia argentea var. cristata,
used for bedding out, has a fasciated flowerhead and can be
raised from seed.