What’s this strange growth on my rose?

Thanks to Master Naturalist Marc Opperman for sending this in!

The stems on his American Beauty rose seem to be mashed together, then a single stem splits into multiple ones.  If you look closely, you’ll see that there are spots where several buds occur in the same location, at a single node, rather than being separately spaced out on alternating sides of the stem, the way they normally would.  Those spaces between alternating buds, between nodes, are known as internodes.  And here, the buds are all piled up on top of one another, at the same node, so, the internodes are virtually nonexistent.

The lower portion of the stem, before it starts to separate and grow apart, appears somewhat flattened, or at least not cylindrical, the way stems usually grow. It appears that growth…cell division, is happening, but for some reason separation…cell elongation, is not.  In order to explain what’s going on here, we need a quick lesson in plant hormones.

Cell division in plants occurs only in localized areas called meristems, or what we gardeners refer to as “buds.”  Not only does cell division only occur in these buds, it’s actually controlled by them, through the influence of the plant hormone auxin, and this effect on plant growth is known as apical dominance.

Auxin is produced by the apical bud and sent downward through the plant. The further from the apex, the lower the concentration of auxin.  So as the apical bud gets further away, the lateral buds are less influenced by it.

Once the apical bud, at the tip of the stem of the growing stem, gets far enough away, the lateral buds begin cell division, and will begin to exert their own apical dominance over any lateral buds that they might create.  The apical meristem produces a finite amount of cells, then those cells elongate, due to the influence of another plant hormone, gibberellic acid.

Each plant species has its own unique pattern of growth, or cell division and elongation, which creates the plants natural growth habit to be either compact or tall; bushy, or more tree-like, or whatever the genetic coding is.

But sometimes things happen and that genetic coding gets “messed up.”  Which leads us back to Marc’s rose.  Some type of anomaly has occurred where several buds have formed at the same node and the buds are separating.  Cell division is on overdrive, but cell elongation isn’t happening at all.  Something may have slightly damaged the apex and caused this response, or it could be a genetic anomaly that occurred during propagation.

As with genetic anomalies in animals, we often aren’t sure what causes them in the first place, and once the genetic coding is changed, it rarely reverts back to normal.  Usually the new pattern becomes the norm and repeats each season with new growth.