It is odd that a subject that would have been familiar to botanists across Europe in the nineteenth century should be now so generally neglected. Perhaps it was always a little too vague, deriving from the Greek ‘teras’ a monster or marvel, and covering such oddities as proliferous flowers (those with extra flower or leaf buds growing from the middle or sides of a flower), fasciation (the broadening of stems, flowers or even roots to resemble a ribbon or bunch of sticks) and the replacement of one plant organ by another.
By the time Maxwell T. Masters was writing in 1869 the number of papers in learned journals was already too many for him to collate, though his work ‘Vegetable Teratology’ must be considered a good attempt at covering the available literature (It does not just deal with vegetables but the vegetable kingdom as a whole.)
Without the benefit of genetics a large number of theories were promoted by those studying plant aberrations such that a whole new vocabulary emerged to express these theories, but these quickly became out of date and difficult to understand, dealing as they were with only a partial understanding.
Apart from the advances in genetic understanding other advances in the interactions between insects and plants in the form of galls have been properly studied, by such organs as the British Plant Gall Society so that we know about the true cause of the artichoke like structures that grow at the tips of branches of yew. This was something that Masters could only have suspected. (For details of the British Plant Gall Society, please e-mail me)
Some geneticists seem to consider that Genetics is the science which allows us to understand all the non-galled aberrations that the Victorians were so good at spotting and recording. Obviously the work done on the mutations in Arabidopsis allows odd plant spotters to come to a closer understanding of many forms in other plants. Hundreds, perhaps thousands, of such mutations have been described and explained.
But this must only be assumptions, and perhaps this is an area where speculations can still be described as teratological. There are also other cases where plants produce structures in individual leaves or non-seeding flowers and so there is no access to proving a genetic base (I believe). Of course genes will be involved in the production of such aberrations but it will not be possible to prove which genes and it is unlikely that such structures will tempt the geneticists. Surely this is legitimate ground for modern plant teratologists.