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.
A "Monstruosa" variety is similar to a "Crestata", but with a much greater loss of symmetry in a cellular growth: here it's not possible to find a unique apical meristem: there are many cellular growth centers from which cells are produced in many direction. As a result, we can have giants or deformed organs, crested or fan-shaped ones, etc.
Monstrosity leads to random production do differentiated organs in not normal spots of the plant, só that it looses its normal growth habit.
Examples of monstrosity are abnormal leaf growths, spiral twists in stems ribs growth, giant organs, double flowers, an abnormal absence or reduction of spines, etc.
As “Crestata” (crested) plants, Monstrous plants are the result of a disorder in the growth centres of the plant: the meristems. 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.
Monstrosity, anyway, unlike cristation, doesn't imply fasciation, namely production of flattened organs. Actually, this phenomenon causes a systemic mutation in all meristems of the plant. After that, all these growing points start to behave abnormaly, as if the plant had a tumor. As a result, the plant starts to form knots, bumps, abnormal branches, and become completely different from how it would look like without a mutation.
So, unlike cristation, where the plant develops only one odd organ, in monstrosity all the plant is affected, and it's often impossible to recognise the originary species of a “monster” plant.
Although many mechanical causes and environmental factors that contribute to the development of monstrosity, 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 monstrous plants, is that, because of their slightly different appearance than normal individuals, are less adapted to the originarily ideal environment of their species, so they result to be more sensitive.
Anyway, in the end, monstrous plants require a "harder" treatment. For example, an abundance of fertilizer or water can cause wounds. Bumps and knots, for their weird shapes, are more fragile and it's easy to break them.
Monstrous plants are supposed to be rather more slow-growing than crested plants, which grow faster.