We cannot talk about vernation types
not seeing the midrib as it is presented on the second drawing.
It can as well be a half of a leaf
The third drawing (convolute) is
what I thought about (but I was afraid to say) -
that the term "convolute" may refer
only to at least two objects
like one leaf inside another one or
a spadix wrapped by a spathe.
Anyway in my cord photos, the third
type, although probably not occuring in Araceae
is possible, so it must have a name
It's becoming complicated...
These drawings are from William T. Stern's Botanical Latin,