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.
Synanthy the abnormal fusion of two flowers.
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.
Floral Virescence where the flowers turn green in colour but retain form and function.
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.

Peloria is where the petals of a normally bilaterally symmetric flower takes on a radial symmetry. They are then said to be Peloric. Thus, double-flowers are not 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  (although your Author had always thought that there was some element of truth about Lamarckism), where the environment leads to heritable changes in the genome - 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).

Peloria is frequently found in Foxgloves, where usually it is the topmost flower which reverts to the older form of flower shape with radial symmetry rather than the more recently evolutionary development of bilateral symmetry - such as normally exhibited by Foxgloves, Vetches, and a great many other flowers. It is usually only the topmost flower which can exhibit peloria; all the others are normal with bilateral symmetry.

Peloria is more usually of epigenetic origin and recessive (more infrequent than transmissable), although it can be instigated by environmental happenings. These changes to the epigenome can persist in the population but only reveal themselves by a peloric flower appearing from time to time.
Peloria can also be exhibited by several species of Orchid, such as Phalaenopsis, flowers in the Mentha genus (mints), and others such as Gloxinia, Pelargonium, Snapdragon and Primula auricula. Some, such as peloric gloxinias, are especially bred for sale in garden shops.

In horticulture, some plants are especially bred to have doubled flowers, in which case the phrase 'flore pleno' is often suffixed onto their name. Doubled flowers can occur naturally in some wild flowers, where extra petals are to be found growing within the bounds of the normal outer petals. They are produced by a genetic mutation where the sexual organs are replaced by more petals, often many more than the mere 'doubling' suggests. But these plants, both wild and cultivated, are useless to bees, for there is no nectar and the bees will waste their energy in stumbling about trying to find any.

Fasciation is where some part of the plant is erroneously repeated in a long line, resulting in either several fused stems in a linear bundle (like computer ribbon-cable) or multiple flowerheads, again repeated in a linear fashion so as to resemble a much wider flower. Think the old-style toilet brush. 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 to grow into 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 such damage is occasioned 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. Sometimes 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.

Phyllody (aka phyllomorphy or frondescence and sometimes chloranthy) is an abnormal growth on a plant where the flowers should grow but are instead completely replaced by leaves (all the sexual parts are absent) or it can just affect parts of the flower such as half the petals leaving the rest intact. If phyllody affects the whole plant then it can make the plant sterile, unable to reproduce, simply because it now has no female organs (the male organs, anthers, are very rarely affected by phyllody possibly because they are the most highly differentiated organs in flowers). But phyllody can leave some flowers unaffected instead. Phyllody is usually caused by an infection, such as either a phytoplasma or a virus, but it can also be caused by any environmental conditions which result in an imbalance of plant hormones (of which there are many dozens, many working in a regulatory fashion - both for and against - a balancing act).

Phyllody is common in members of the Plantago genus such as Ribwort Plantain, as well as in some other plants such as Hop, Dahlias or Dandelions. It is more commonly expressed in those flowers which are polypetalous (with more than one petal) rather than the monopetalous plants which have but one petal (the petals being fused into the form of a bowl or tube) such as Daffodils.

The causes of phyllody are manifold, including phytoplasmas, virii - such as those which cause Rose rosette disease, fungi - such as smuts and rusts, water moulds - such as Sclerophthora macrospora and last but probably not least by insect damage. But phyllody can also be caused by environmental factors such as the weather occasioning drought or heat stress amongst many others which may create a hormone imbalance. Applying growth hormones could have the same effect - after all, phyllody is the plant growing parts of itself where it should not - and the right parts grow where they should orchestrated by the inter-play and concentrations of many different hormones, so it is no surprise that upsetting the hormone balances by direct application may result in the plant growing parts of itself where it shouldn't.

Virescence is closely associated with Phyllody, but is in actual fact quite different. It occurs when normally non-green parts of a plant are rendered green by a green pigment (usually chlorophyll). Thus flowers which are normally colours other than green are coloured green. Apart from the green coloration, the flowers are normal.

Your Author thinks this does not apply to those plants which normally have green-coloured flowers, such as those of Moschatel, Lady's Mantles, Dog's Mercury, Bog Orchid, Parsley Piert, White Bryony, Golden-saxifrages, Common Twayblade, some Hellebores, etc.

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