Who's the creative team on this issue? Swamp Thing is drawn after Wrightson's style, but it's clearly not Wrightson (and not just because of the dedication to him at the end).
I imagine this crossover must be from the seventies because this Swamp Thing conforms to Len Wein's characterization in that he thinks a lot but doesn't talk much. (IIRC the only things that Wein's Swamp Thing would utter out loud were "No!" and "Arcane!" and such.)