In a previous post about monarda fistulosa, also called bee balm, we reported our amazement to observe that on a few of our plants a second, smaller flower head had sprouted from the first. The phenomenon repeated itself this year, two examples of which are being pointed out in the picture at left, which may, as usual, be clicked to see a larger version. Ever since then we have scrutinized every patch of bee balm we come across for such oddities with the enthusiasm of a child questing for a fourleaf clover and the luck it is said to bring. And we have discovered that these two-headed monarda are not so very rare (at least among the native variety) for all that it seems difficult to find mention of them.
Searching the web brings us uselessly to our own blog or to monarda on lists of bee-friendly plants or tips on growing monarda but no mention of the occasional tiered flowerheads. We have only found one picture of a red variety with a tertiary head and a page discussing anomalous secondary petals among cone flowers.
What causes a subordinate head to develop?
Does it always develop near the center of the supporting head?
Does its formation somehow suppress or make unlikely another head on the same tier?
What limits the number of tiers?
No answers. No answers. Is there not a grad student in botany somewhere studying this?
We conclude with the picture at right, our best example thus far found, having a secondary head about the same size as its primary. Perhaps it will sprout another?
Edited 2014-Jul-30 : Please, see the reply below from infamousginger for an explanation.