Giant Lochkovian cooksonioids from circumpolar Gondwanan strata of South Africa

Abstract

Earliest land plants (i.e. rhyniophytoids) are characterized by minimal architectural complexity, generally associated with diminutive size. The absence of larger forms has commonly been attributed to morphological constraints limiting increased vertical growth. Plant fossils from a recently discovered locality from South Africa, formerly situated inside the Antarctic circle during the Lochkovian (Early Devonian), led us to question this paradigm. Here we describe two new plant taxa, Vuvuzela enkulu gen. et sp. nov. and Tympania merrionii gen. et sp. nov., distinguished by unusually thick axes and large cooksonioid‐type sporangia, with the former also exhibiting the longest continuous axis yet recorded among rhyniophytoids. Despite their overall architectural simplicity, these plants display markedly different structural organizations, reflecting distinct growth strategies. Quantitative comparisons across multiple size‐related metrics demonstrate that both genera represent genuine outliers among currently described taxa. Furthermore, we show that preservation (i.e. increased fragmentation) and sampling biases are insufficient to explain the apparent absence of large rhyniophytoids at other localities. These findings therefore challenge previous assumptions that rhyniophytoids represented an adaptative impasse due to architectural constraints, ultimately leading to their competitive replacement by the end of the Lochkovian. The occurrence of both the highest plant taxonomic diversity and the largest organisms, in the high palaeolatitudes of Gondwana during the Lochkovian, also raises important questions about the ecological drivers of early land plant diversification.