Differences in flower branching in compass plant?

While most of the compass plants (Silphium laciniatum) I see in garden and tallgrass prairie settings have very little branching in the flower stalk with the flowers close to the stalk, some of them have significant branching similar to prairie dock (Silphium terebinthinaceum). Does anybody know what causes these differences? Though I suspect this plasticity comes from environmental conditions, these very different inflorescences often occur close by one another (picture attached).

I found this interesting article from Fay and Throop that gave some answers with rosinweed.

Fay, P. A., & Throop, H. L. (2005). Branching responses in Silphium integrifolium (Asteraceae) following mechanical or gall damage to apical meristems and neighbor removal. American journal of botany, 92(6), 954–959. https://doi.org/10.3732/ajb.92.6.954


Very interesting. Do you suppose it’s also possible for some S. terebinthinaceum (or other congener) genes to be floating around due to some past hybridization even?

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