You’re right that the word doesn’t seem to appear in any standard dictionaries. It is, however, relatively easy to guess at both its meaning and its derivation.
If we start with the derivation, it is quite clearly related to ramify, as the quote in Josh’s comment to the question states. Ramify ‘to branch’ is from Latin rāmus ‘a branch’ + the productive suffix -(i)fy ‘make’; so ‘to make branchy’ or something like that.
In Classical Latin, the diminutive of rāmus was rāmusculus ‘small branch’; but later on, in post-Classical times, another word with the same meaning also appeared: rāmiculus ‘small branch’.
This word was formed with the very productive diminutive suffix -(i)culus, in exactly the same way that artus ‘joint’ formed its diminutive articulus ‘small connecting part, smaller unit in a larger context’. The English form of that word (borrowed from Old French) is article, and the highly rare but attested English form of rāmiculus taken on a similar journey, is ramicle ‘small branch’.
In the same way as article corresponds to the verb articulate (though the meanings have diverged), ramicle likewise corresponds to the verb ramiculate, which then means not only ‘to branch’, but ‘to split off into many tiny branches’. If I were feeling humorous, I might even suggest ‘to twig’ (but I won’t, because that means something else).