Moved from Rhopalosiphum.

While a handful of Rhopalosiphum species feed on cattail, the most common is R. enigmae.
This comes with a few caveats though:
A second cattail specialist, R. laconae, is known from Virginia through South Carolina, though I suspect it's synonymous with R. enigmae (working on DNA at the moment, hopefully will clear this up in the next few months).
Rhopalosiphum nymphaeae and R. padi are also known to feed on cattail. Rhopalosiphum padi is green with red between the siphunculi, while R. nymphaeae is generally covered in wax and has inflated siphunculi.

So based on the host and gestalt, I'd be comfortable calling this R. enigmae, at least as we understand it at the moment.

Moved from Aphids.

Rhopalosiphum