For the various Mutations and abnormalities in Plants:

These abnormalities include:
Fasciation where the stem becomes ribbon-like or the flower elongated.
Double-flowers where petals and other flower parts are multiplied.
Phyllody (aka Phyllomorphy / Frondescence) where parts of the flower may develop into leafy structures instead.
Virescence / Floral Virescence a green pigmentation in parts of the plant not normally green. If this occurs on the flower, it is known as Floral Virescence.
Proliferation where normal plant parts grow in abnormal positions.
Separation and division of parts where normally 'entire' leaves are lobed instead.
Abnormalities in number where flowers may have extra petals or other parts.
Abnormalities in size where plants grow far larger their normal maximum size.
Abnormalities in shape where plants assume abnormal shapes.
Anomalous Colourings including Aureate forms where yellow replaces green.
Variegation and Chimeras where some abnormal patterning has resulted.
Peloria where normally bilaterally symmetric flower petals take on radial symmetry. They are then said to be Peloric. It has recently been found that peloria is not a trait propagated by DNA, but instead involves an  epigenetic process of silencing a specific gene by DNA methylation in the environment. The peloric nature is happily passed on between generations, just like it would be if it were down to changes in the DNA sequence. But the DNA sequence remains un-altered in epigenetic changes. This is similar to the once discredited  Lamarckism , where the environment leads to heritable changes in the genome and which is now found to be not totally without foundation, although specific examples are rare (and most examples involve epigenetic changes to the DNA - methylation)

Fasciation is where some part of the plant is erroneously repeated in a line, resulting in either several fused stems in a linear bundle (like ribbon cable) or multiple flowerheads, again repeated in a linear fashion so as to resemble a much wider flower. Fasciation is derived from the latin Fasces meaning a flat bundle of wooden sticks.

Fasciation is a result of an aberration in the apical meristem - the growing tip of the shoot which consists of undifferentiated cells (cells which have not yet been assigned as those for petals, veins, anthers, etc etc). The apical meristem can become damaged (by several means - physical damage by insects, fungi, bacteria, nuclear radiation, weed-killers, un-suitable growing conditions, heavy metals in the soil, etc) when disrupted growth can occur. Fasciation can be one result of this abnormal growth pattern. Fasciation can affect just the stem, just the flowerhead, or both together where the whole plant can be fasciated.

Fasciation can also be an inherited condition, where several nearby Daisies or Dandelions (or any other plants) are fasciated. A few plants sold horticulturally have been specially bred to be fasciated, such as the Amaranth known as Cockscomb celosia which has gaudy colourful fasciated flowerheads. The Fantail Willow used by Japanese flower arrangers has twisted flattened branches, the result of in-bred fasciation.

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