In botany, "monsters" are the varieties "Monstruosa", "Crestata", "Variegata. These unusual plants arouse fascination in botanists and "Cactophiles" for their weird shapes and their striking appearance due to particulare colours or unusual organs: collectors are always on the lookout of them. Teratology is the science that deals with anomalies that occur in both plant and animal world.
"Crestata" varieties are the result of a phenomenon called "Fasciation".
Fasciation is an abnormal growth condition of vascular plants where a meristem produces new cells just in two directions, and becomes elongated and flattened perpendicularly to the normal direction of cellular growth. Meristems are groups of cells, located in vegetative and flowering buds, at the top of the plant (apical meristems, which are the ones who ensure growth in height), and all along the stems to ensure their growth in width. They are necessary to ensure the growth of any plant. In these cellular tissues, cells remain undifferentiated, which means that they don't have a specific function in the plant. For instance, a leaf cell is a differentiated cell, because it has a role in the plant: that is to supply to all the leaf functions, such as photosyntesis, and because it has the specific features of all the leaf cells. On the contrary, meristems cells don't have a specific function and don't belong to any specific cellular tissue of the plant: they are “young cells” present in different spots of the plant, which have the function to produce new cells, ensuring growth in height and width of the plant and the production of new branches, leaves and flowers. Normally, a meristem cell multiplies producing new cells in all directions around a central point, where there is the meristem cell of origin, the "first cell". In the phenomenon of the fasciation instead, new cells are produced only in two directions, perpendicularly to the growth direction of the interested organ of the plant, producing strange "monsters" that we can sometimes (rarely) observe in Spring, while we have a walk in a daisy field: we will find out a very unusual flower...
To sum up, fasciation is an unusual phenomenon that turns a normally cylindric stem into a flattened one, which can turn into a fan, a ridge, a wedge or crest when the flattened organ curls into crest that can envelope into complex forms like brains!
A "Crestata" variety is a variety in which a phenomenon of fasciation occurs, creating crested, peculiar shapes of an organ of the plant (generally the stem),after a genetic mutation or a disturbance to the normal activity of the meristem by insects, pathogenic organisms, hormonal imbalances, thermal shocks, etc.
"Crestata" varieties are rare phenomenons. Anyway, there are genuses of plants which manifest these oddities more frequently: for example Aloe, Acer, Aloe, Cannabis, Celosia, Delphinium, Digitalis, Euphorbia, Forsythia, Glycine, Primula, etc. But, in particular, this phenomenon is really more frequent in cacti, namely members of the family of Cactaceae.
In plants of the family Cactaceae, "Crestata" varieties are very frequent. There are fan-shaped, brain-shaped when they get elder, and wavy crests.
When fasciation occurs, the plant increases its growing rate and grows faster: this could be because of the hormonal imbalance or maybe for the increased phosynthetical surface which provides a major quantity of nutrients in the plant due to the modification of the stem. So the crest grows fast and the flattened to surface starts to envelope and twist into complex forms like waves and then brains.
Sometimes, when the "brain phase" is reached, many normal stems starts to grow from new apical meristems formed in the "brain". This is called "defasciation", another mysterious phenomenon: the reasons why it occurs are unknown.
Fasciation and formation of crests occur in different growth phases depending on the species: In columnar cactus, such as Saguaro (C. gigantea), fasciation occurs late, when the plant is elder. In globose and, in general, in smaller cacti, fasciation can occur in any phenological phase, even in "baby plant", with only one leaf formed.
Moreover, another interesting feature of crests is that they maintain the physiological age of the moment in which they are formed by the plant. To be clear, a crest formed by a young plant may could remain not capable to bloom, or may conserve a juvenile arrangement and dimension of the areoles, even when the rest of the plant reaches maturity.
Although many mechanical causes and environmental factors that contribute to the development of fasciation, such as extreme temperatures, wounds, infections of pathogenic organisms and genetic mutation, have been identified, they are deemed to be just concauses of this oddity. Possible main causes are genetic casual mutations and hormonal imbalances. Genetic mutations are the most probably main cause: it's sure, anyway, that this kind of phenomenons are eased by the simultaneous occurance of multiple factors. For instance, an infection and an hormonal imbalance can both contribute to cause a genetic mutation that creates the deformity.
A peculiarity of “Crested” plants, is that, because of their slightly different appearance than normal individuals, are less adapted to the originally ideal environment of their species, so they result to be more sensitive. Anyway, in the end, crested plants require a "harder" treatment. For example, an abundance of fertilizer or water can cause wound. If you desire the crest to develope more, just prune off normal shoots: this will help the crest grow better. It's not known if fasciations and so monstrosities and crests are inherited. If deformed part of these plants are pruned off, the condition appears again. Anyway, grafting once the plant evelops this deformities is a way to transmit this condition to another plant.