The last plant in our Herculean trio certainly represents the Hydra. One of Hercules’ labours involved slaying this multi-headed snakelike monster. The problem was that as soon as he chopped off a head, two of them would grow back in its place. Kind of like in Voynich studies, where every answer brings more questions.
On the left, we see Hercules and his companion fighting the Hydra. Descriptions of the Hydra and its amounts of necks, as well as how they behave, vary greatly. In this example, the monster has several heads, as well as a number of snakelike appendages and a larger, split tail (bottom right).
The same can be seen in our plant. This hydra has two of its heads remaining – represented by the green leaves – swooping around on long necks. The roots represent dead necks or random appendages, like they can be seen in the left image. Finally, our plant’s root also ends in a split “tail” on the bottom right.
If the resemblance so far hasn’t convinced you, maybe this last detail will: the middle neck, which has just been chopped off and grows back as two.
I’m not sure about a plant ID. Perhaps the roots are supposed to represent a tree with hanging roots, like several Ficus species. Pictured here is Ficus elastica. An argument could be made for the leaves looking similar as well, but I can’t be certain until a convincing label reading has been found.
Additionally, I suspect there may be some practical mnemonics at work here as well: those mnemonics that give a hint about the plant’s use or purpose. In this case, the leaves look especially “fibery” and the roots represent ropes or even a piece of fabric. In fact, the “hairs” around the leaves look a lot like those on the roots in O’Donovan’s 2012 discussion of the hempen-fibre group.