Webster’s 1913 has no entry under this spelling.
Shades of meaning
Fernald has no entry of its own for unadorned; he lists it under clear.
Where he writes about it:
Perspicuous is often equivalent to plain, but plain never wholly loses the meaning of unadorned, so that we can say the style is perspicuous tho highly ornate, when we could not call it at once ornate and plain. — from clear