Proposed mnemonic devices

[Koen G]

Don.
You define You are not allowed to view links. Register or Login to view. "Lunaria annua".
I see the root of this plant as an octopus, leaf-floats (bobber). In sum, it indicates an aquatic plant.

Wladimir, those are two animals facing each other, but clearly not lions like people say. There are 12 arms, that's too many for an octopus.

You can see an octopus in this plant:
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It has eight arms, a "head", and even little "suction pads" on the arms.

Below that octopus is a squid, and left of the octopus is a jellyfish. 


Don
Like I said before, you have a good eye for finding meaningful parts of the images, but everything in the imagery speaks against them being created by an English speaker. 

Also, speaking as a linguist now, I'm afraid that the chance is very small that all the names you propose for your plants were the primary names for those plants in one specific area during the 15th century.  Names for plants, birds, insects... can vary from one village to the next a couple of kilometers further.
So if you looked for 15th century attestations of the names you propose, and can track the areas where they were found, you could theoretically limit the place where the MS was produced to a rather specific area. But I'm not sure if that's possible.