Those ‘special’ flowers
“There can be little doubt that of all European wild flowers few species can rival the indigenous orchids in beauty and variety of form and colour. These attributes, coupled with the adventurous journeys one must undertake in searching for some of the rarer species, have endowed orchids with a special glamour all their own. Often some rare and lovely species has its particular habitat in a region of great natural beauty, remote and difficult of access but infinitely rewarding. The pursuit of such gems is in truth a treasure hunt.”
From the Introduction to Orchids of Britain and Europe

Southern marsh-orchid (Dactylorhiza praetermissa), photographed by Three Points of the Compass on the London Countryway
Beyond a couple of field guides or home reference works, some groups of flowers or habitats encourage the inclusion of specialist works on the book shelf. These are two such. One to a group of flowers that has always fascinated me, the other to those plants that hang on in often challenging regions, rarely below 1500m in elevation.
Some flowers hold a rare fascination. Despite Orchidaceae being the second largest family of plants in the vegetable kingdom, none are commonplace, though they can be found in almost every habitat other than glaciers. A Field Guide to the Orchids of Britain and Europe contains a key to the plants along with pretty good species descriptions opposite page size drawings.

The area covered by A Field Guide to Orchids of Britain and Europe with North Africa and the Middle East
The same groups of plants can also, to a large extent, be found the Collins Pocket Guide to Alpine Flowers, however their coverage is far more cursory. This book was lauded on its release as the only portable guide to the flowers of mainly mountainous regions.
Books from my shelves:
Collins Pocket Guide to Alpine Flowers of Britain and Europe, C. Grey-Wilson and M. Blamey. Haper Collins, second edition 1995. ISBN 0 00 220017 1
A Field Guide to the Orchids of Britain and Europe with North Africa and the Middle East, J.G. Williams, A.E. Williams, N. Arlott. William Collins, 1978. ISBN 0 00 219314 0