Ernst Mayr, Systematics and the Origin of Species
(New York: Columbia University Press, 1942; rpt. 1982), p. 103:
[N]o system of nomenclature and no hierarchy of systematic categories is able to represent adequately the complicated set of interrelationships and divergences found in nature.
Heinrich Heine, The Harz Journey
(tr. Charles G. Leland):
It vexes me every time, when I remember that even the dear flowers which God hath made have been, like us, divided into castes, and like us are distinguished by those external names which indicate descent and family. If there must be such divisions, it were better to adopt those suggested by Theophrastus, who wished that flowers might be divided according to souls—that is, their perfumes. As for myself, I have my own system of Natural Science, according to which, all things are divided into those which may—or may not be—eaten!