Of Panicles, Corymbs and Cymes
and corymbs are
two very important terms used in botany, and in the study of asters and
goldenrods in particular. We use those two terms to help
distinguish between different species.
These two terms have fairly precise
meanings, and if used strictly, we could not say that they apply to
asters or goldenrods in all cases. The capitulescences
of many asters or goldenrods that we will encounter in the field may not
seem to fit either of the two broad types. Either growing
conditions or the genetics of a particular species may cause a
particular plant to have what seems to be an underdeveloped
captitulescence, one that is "sort of" a corymb or "sort
of" a panicle. Or, it may not be possible to say at all what
the capitulescence looks like.
|According to this image of Ionactis linariifolius, which was growing in a dry, upland woods, could we say that the capitulescence is either like a corymb or like a panicle? Not easily. Growing conditions for this single-stem plant were too dry to allow it to develop a full corymb.|
|In this example of Symphyotrichum racemosum, the capitula mature from the distal end to the proximal end of the inflorescence branches. However, for panicles, the capitula should mature in the opposite direction: from proximal end to distal end. This is quite typical of many asters and goldenrods. Yet, we say that this species has capitulescences in the shape of a "panicle".|
|In this specimen of Doellingeria umbellata, the capitulescence is definitely round-topped, and we could argue that it is a "corymb". However, the longest inflorescence branches aren't the lowest ones, which is what we would expect from a true corymb.|
corymb and panicle are theoretical constructs, and as we
know, plants don't read books. So, there are two other
similar terms that allow us to describe a greater number of the
capitulescences of asters and goldenrods: "paniculiform"
and "corymbiform" . . . having the appearance of, but not
necessarily meeting the strict definition of a panicle or of a
corymb. That is, being "panicle-like" or
We can say, for example, that the capitulescence
canadensis is paniculiform,
whereas that the capitulescence of Doellingeria
umbellata is corymbiform.
created yet another term to deal with the fact that the
"panicles" so often found in some asters and goldenrods don't
quite fit the definitions. That is, the capitula
mature from the distal ends of the branches
rather than the proximal ends. We will
use the definition of the term "cyme" by Gleason and
"A broad class of inflorescences characterized by having the terminal flower bloom first, commonly also with the terminal flower of each branch blooming before the others on that branch."
Please refer to the above picture of Symphyotrichum racemosum for an example.