Cristation, cresting or fasciation is an accident of nature that occurs in either vegetative or flowering buds, the former bearing new stems and leaves and the latter, well, flowers. This may seem quite obvious to most of you, but I must say that I am surprised how many of my horticulture students are not aware of this small fact. To confuse matters you can get mixed buds, but inside each of these will be smaller flowering and vegetative buds.
What we see with fasciation deformity is a flattening of the flower or stem although it can happen to fruit too. It is not a particularly common abnormality and I must say that when I see examples of it, I think it is quite quirky and leave them where they are. But then I am an individual who loves the abnormal mind you, while others prefer the status quo. If we were not all different, life would hardly be worth living would it?
Buds, both vegetative and floral, are technically known as plant meristems. They are where cell division takes place. If we dig back into the recesses of our grey matter we may remember that plants grow very differently from animals in that they have very localised areas where cell division takes place, plant meristems. These occur at the tips of roots, stem tips (buds), floral and reproductive parts, and in woody plants, one that makes bark and one that allows stems and roots to increase in diameter. The latter two are called cambiums, the cork and the vascular cambium respectively.
The meristem of flower buds and vegetative buds (and root tips for that matter), are dome-like in appearance and microscopic. Yes, most of the cell division that creates these structures occurs in these tiny spaces.
What happens and what can cause fasciation?
It is generally now believed that a simple mutation in one of the cells in the meristem of a plant leads to fasciation, the formation of these odd plant parts.
“…instead of the meristem being formatted to produce a round stem the mutation causes a disruption in between-cell communication and the flattened meristem results.” (See Reference 1).
Such plant parts often also have a larger circumference than their more normal counterparts and actually tend to be heavier.
Many would like to tell you that the fattened stem is actually two stems fused together, but this is not correct. As you can see from some of the photos on these pages, the leaves also tend to be much smaller by comparison to a normal plant, an example of the cascading effects that can happen from one simple modification.
A number of factors can cause fasciation, both biotic and abiotic, and one of them is not accidental over-spraying with a hormonal herbicide, as some would like to tell you. Most of us have seen spray side-effects, at some time in our lives, whether it was us who accidentally over-sprayed or one of our fellow workers. Yes, the growth is distorted but really it looks more like fungal damage in appearance but with abnormally thickened growth in nature, yellowing…you name it, over-spray can do it.
With fasciation though, isn’t it great that one odd-ball cell can lead to such amazing manifestations of nature – go the odd-balls I say, they rule!
A particular euphorbia we grow at Larnach Castle is prone to fasciation, shown in the photo above. The stems can become particularly wide and fat, so I tend to cut them off because they flop to the ground and smother the plants beneath them. Interestingly, as you can see, the flower head is unaffected.
In some species fasciation is simply a genetic mutation and a classic example is Celosia (see photo). The fasciated flowers seem to be at no big disadvantage evolutionary wise, because the mutated flowers quite happily get pollinated and produce viable seed.
In the lab they have managed to create fasciation through bombardment with x-rays but in nature the most common causal agents are believed to be pests and diseases. Mind you, the former are now considered primarily to be the vector, the carrier of the disease. It used to be considered that a number of insects could cause these effects, but no more.
Phytoplasma is the main culprit in causing fasciation
The most common fasciation-causing organism is now generally thought to be a phytoplasma, a microscopic little thing that sort of falls between a virus and bacteria.
The desirable cacti with obvious fasciation are largely caused by these guys. Bacteria though, have been shown to be the causal agent in sweet peas and petunias, and with Lilium henryi it is nematodes! (See Reference 2).
Viruses and fungi are also thought to be responsible although I found no evidence showing definitive proof for either, but lots and lots of people saying it was so! The environment itself can amazingly also achieve these results. It is evidently not uncommon for a deficiency in zinc to cause this effect and strong temperature fluctuations can also cause it in some species, for example in hyacinths (when low temperatures are followed by high in its case). Interestingly it can also happen with strawberries through the same mechanism.
Ahh, the effects are so variable, like most of the things that happen in nature; nothing is simple.
What do you do when you see fasciated plant parts?
Admire it – or just cut it off?
Well, first enjoy looking at something that you do not see very often. Fasciations really are quite striking, a quirk of nature almost Dr Seuss-like in their appearance. The universe of reality sometimes overlaps the universe of fiction, the boundaries are not as defined as we would sometimes like to believe.
If you do not like the look then simply remove the offending plant part at the base, or just below where it starts. I have been known to do this myself sometimes, with a Euphorbia that is prone to fasciation at Larnach Castle where I manage the gardens. Its stems are of the weightier nature so tend to collapse to the ground and well then, look a little unsightly whilst smothering the plants underneath.
If you are super worried about it spreading, just ensure that you use good hygiene practices and dispose of the offending material in a manner that makes you feel as though you have given it no chance of survival (there is always the option of sending it off to the local green waste site where it may make its way to someone who may enjoy the effect it creates).
And, of course, do not propagate from this material. As insects are often the vector of the causal organism you could also use insecticides, but I so hope that not one of you thinks of going down this line of defence; the negatives of such actions far outweigh the small benefits.
If you like it, do the opposite of everything said above and enjoy those odd shaped flowers and ribbon-like stems with their small nubby leaves. Some such plants have become particularly desirable, such as fasciated or crested cacti, as mentioned, and Japanese willow Salix udensis ‘Sekka’. Nature is meant to be weird and wonderful; it’s part of what makes our planet so great.
[Reproduced with the kind permission of Commercial Horticulture, New Zealand’s nursery industry magazine]