Rhizome and leaf anatomy of Rhizocaulon huberi H.-J. Gregor (Cyperaceae, Miocene) and nomenclature of the genus Rhizocaulon Saporta ex Schimp. et Schenk

Abstract

Rhizocaulon huberi H.-J. Gregor is redescribed based on new specimens from the type locality of Rátka (Miocene, Hungary). The material consists of rhizomes, roots, and leaves in physical connection. The roots branch from the rhizome from all sides and their primary cortex has radial strands of tissue separated by lacunae of schizogenic origin or resulting from tangential lysigeny. Tristichously arranged leaves that form a pseudostem are dorsiventral with internal aerenchyma. The type material of R. huberi is most probably heterogeneous (it contains septate rhizomes with roots branching in whorls which do not belong to the same plant). Poaceous affinities proposed formerly for R. huberi can be ruled out on account of phyllotaxis. Rhizocaulon huberi is probably a representative of the Cyperaceae (with similarities to Diplasia Rich.), although this conclusion should not be uncritically extended to the other representatives of this fossil-genus. The first valid publication of the genus Rhizocaulon was in 1885, so it should be cited as Rhizocaulon Saporta ex Schimp. et Schenk. Rhizocaulon brongniartii from the Oligocene of southern France is selected herein as the type species, which allows the preservation of the current understanding of Rhizocaulon as a fossil-genus for permineralised rhizomes of monocotyledons. Andrews’ (1955) choice of the Cretaceous species R. macrophyllum as the type of Rhizocaulon is based on an illegitimate name and is thus null and void.