Tournefort, who lived in the second half of the 17th century
(1656-1708), is generally considered as the author of genera in
systematic botany. He adopted, what was at that time the general
conception and applied it throughout the vegetable kingdom. He grouped
the new and the rare and the previously overlooked forms in the same
manner in which the more conspicuous plants were already arranged by
universal consent. Species were distinguished by minor marks and often
indicated by short descriptions, but they were considered of secondary
importance.

Based on the idea of a direct creation of all [34] living beings, the
genera were then accepted as the created forms. They were therefore
regarded as the real existing types, and it was generally surmised that
species and varieties owed their origin to subsequent changes under the
influence of external conditions. Even Linnaeus agreed with this view in
his first treatises and in his "Philosophical Botany" he still kept to
the idea that all genera had been created at once with the beginning of
life.

Afterwards Linnaeus changed his opinion on this important point, and
adopted species as the units of the system. He declared them to be the
created forms, and by this decree, at once reduced the genera to the
rank of artificial groups. Linnaeus was well aware that this conception
was wholly arbitrary, and that even the species are not real indivisible
entities. But he simply forbade the study of lesser subdivisions. At his
time he was quite justified in doing so, because the first task of the
systematic botanists was the clearing up of the chaos of forms and the
bringing of them into connection with their real allies.