Escaping the voluntary constraints of “tyre-track” taxonomy

Abstract

Although conceptual whole-plants are occasionally reconstructed, disarticulation means that palaeobotanical taxonomy remains primarily the preserve of fragmented organ-species, each bearing a Linnaean binomial. Thus, a “natural” taxon that would in any neobotanical classification bear a single valid binomial (any other epithets automatically being deemed synonyms) typically is a chimera, consisting of several binomials that are not only valid but also arguably essential, each representing a different organ of the original plant. The situation is further complicated by the fact that each organ can also carry multiple valid binomials that refer to contrasting preservation states, most commonly either adpression or permineralisation. Thus, a fossil plant is obliged to carry the heavy burden of not one but two or more parallel taxonomies. The two opposing logical approaches to clarifying this complex situation are (1) to coin additional formal names for organ-species that are found in multiple modes of preservation but at present are named in only one mode, or (2) to attempt to gradually rationalise parallel preservational taxonomies through detailed character comparison, giving priority to whichever preservational mode typically offers a stronger suite of morphological characters and therefore the greater probability of approaching the biological reality necessary for meaningful evolutionary and ecological interpretation. We illustrate our preference for Option 2 using Palaeozoic rhizomorphic lycopsid genera in general and our antagonism to the recently erected permineralisation stem-genus “Dimicheleodendron” in particular.