Hugh Davies "Welsh Botanology", the first flora of Anglesey, and the first of any Welsh County, can be downloaded from Google Books.
It is a fascinating read, although be warned, as an Anglesey born and educated Welsh speaker, his Welsh is a bit old fashioned, even for 1813, and his Latin is mediaeval, rather than classical, but both are readable.
As someone who has identified Hypericum Androeseum on Llandwyn Island by the scent of the leaves, I particularly liked his disambiguation of "Dail Twrch". Yes, Hugh Davies bach, they really do smell of boars piss!
Half of the book is in English, so non-Welsh speakers should not be put off. His sections on liverworts, mosses and fungi are equally thorough, and the comments (in the Welsh section) on the treatments of common ailments make this a Herbal as well.