Norman Deno explains it:
"At the time of Linnaeus, academic institutions still clung to Latin as an emblem of intellectualism. This is now archaic. A name like Eranthis hyemalis is an internationally recognized name for a plant and belongs to no specific language. It is not a foreign word, and it is specifically not a Latin word, so to italicize it is grammatically incorrect."*
Thank you! Botanical names are Latin-ized!
(All emphases are mine.)
*Deno, Norman C. Seed Germination Theory and Practice, 2nd ed. State College, PA (1993).