A recent acquisition of mine is a copy of Synopsis of the Natural History of Great-Britain and Ireland. This 1795 systematic arrangement of plants in Britain illustrates many of the interesting nuances of early systematic classification, and unlike other classifications of this era, it is printed in English. Coming not long after Linnaeus's original description of the 24 classes of the plant kingdom, this book includes my favorite, Tetradynamia (class 15). The characters for this class (6 stamens, four long, two short) are now used to describe the family known today as Brassicaceae (previously Cruciferae). At this time, the class Tetradynamia was split into two orders, siliculosa and siliquosa, descibed by silicle fruit type versus silique fruit, respectively. This convention is no longer used, as it is now known that fruit type is a poor character. In fact within many Brassicaceae genera, both silicles and siliques may be found.
It's interesting how useful this book is for field identification, and how the characters for the most part hold up well with those used in modern floras. For instance, here the genus Myagrum (now Camelina) is described by an entire valve apex, a character which continues to be one of the most reliable for identification of this genus. The only species listed here, Myagrum sativa (now C. sativa), appears to be the only known species found in Britain at the time. It's not clear from this description if C. sativa was grown as an oil seed crop in Britain in the 18th century, but there is a note about its weediness of flax fields.