Though described as a single species, Pigg
et al noted the wide grade of variation in the involucre morphology, ranging from simple to ones with extensive spines. The involucres also show a spectrum from thin, leafy lobes that display distinct veins to thick lobes with no distinct venation. As specimens of
C johnsonii have a full morphology range between the three involucre types, the possibility of multiple species is hard to prove or disprove. However the authors chose to name a single species because of the continuous gradation present between the distinct morphologies. Of the two sections into which the genus
Corylus is divided, section
Corylus and section
Acanthochlamys,
C. johnsonii is most similar to three species in the latter. Section
Acanthochlamys is considered basal within the genus and the three species,
Corylus ferox,
C.wangii, and
C. heterophylla are all native to southeast Asia. Infructescences of
Corylus wangii, like those of
C. johnsonii, possess narrow lobes with many unbranched and branched spines, while
C. ferox-like infructescences have a highly spiny, prickly surface. Specimens within the simple end of the infructescence morphologic range are most similar to
C. heterophylla. As
C. johnsonii encompasses a wide morphology range within its features, it is possible it may have
diverged out into the modern species. The modern areas of distribution for
C.ferox and
C. heterophylla overlap in the
Sichuan province of China, while
C. wangii has a distinct and separate range in southwest China. Isolated nuts from
Paleocene sediments in Greenland, England, and Montana have been attributed to the genus
Corylus. However all lack the surrounding infructescence that is needed to confirm placement of the nuts in a specific coryloid genus. ==Description==