Ferdinand Christian Gustav Arnold (24 February 1828 – 8 August 1901) was a German lichenologist and taxonomist born in Ansbach, Bavaria. Even as a high school student he showed an active interest in botany: "Ich und August Gattinger ... durchstreiften von November 1846 bis zum Spätherbst 1847, Pflanzen sammelnd, die Landschaft von München nach allen Richtungen." ("August Gattinger and I … roamed across the landscape of Munich from November 1846 up to the late autumn 1847, collecting plants, in all directions.").