> meaning roughly "born of the plow" or "born of a plowed field." That could have fit a flower that appeared in fields shortly after they were plowed in the spring.

True enough, but it remains a mystery as to why VN would use a name that seems to be recorded nowhere else in science or literature.

The evidence I can gather online indicates that "Humilis Alba..." is a cultivar, so I wonder how many could be found growing wild in the mid-nineteenth century.

But even if VN only saw them in a garden, he likely would have been impressed.