Well... the answer turns out to be page 9 of the, errrm, snappily-titled 2007 book "The Curious World of Carnivorous Plants: A Comprehensive Guide to their Biology and Cultivation" (Timber Press) by Wilhelm Barthlott, Stefan Porembski, Rudiger Seine and Inge Theisen. Pretty much as I guessed, it was the plant's set of (apparently thigmotropic) tentacles that convinced them of the match, which is fair enough.
This is consistent with the conclusions I drew in my book, which would indeed predict that (as a Herbal A page) the plant depicted probably is a plant (as opposed to something completely different disguised as a plant). You can also see where the heavy blue paint on the page has been contact transferred across to the facing page f55v (and in the opposite direction too): which is interesting, because f55v is a Herbal B page, and so the two pages were probably bound out of order. And so whereas the blue paint would very probably have been added after being misbound, the green paint might well be original (but it's hard to be sure).
Incidentally, it was the oddly geometrical layout of the sundew-like tentacles on f56r that reminded Stan Tenen of the "1/r" spiral (the inverse or hyperbolic spiral), apparently a useful way of visualising the kind of whole-number fractions used by Ancient Egyptians for their maths. As a yet-further aside, this kind of inverse sequence reminds me of Keely's amazing claims, which form a part of Andrea Peters' book "The Voynich Solution" which I briefly mentioned here. All grist for the Voynichological mill!