Paleobotany

Reconstruction of an enigmatic Pennsylvanian cone reveals a relationship to Sphenophyllales

“…Spores were described as smooth and monolete, resembling Laevigatosporites minor Loose (Gao and Zodrow, 1990). The presence of decussate sporophylls in a Carboniferous strobilus highlighted Tetraphyllostrobus as very unusual in the context of the known structural diversity of Paleozoic plants (Friis, 1992). To that end, the genus was initially considered incertae sedis (Gao and Zodrow, 1990) and subsequently it has been treated as a progymnosperm, sphenopsid, sphenophyll, or noeggerathian (Bek and Šimunek, 2005;Wang et al, 2014;Pfefferkorn and Wang, 2016;Wang et al, 2017;Libertín et al, 2014Libertín et al, , 2021.…”

“…For example, strobili with affinity to Calamitales and Sphenophyllales (extinct horsetail relatives) exhibit whorled sporophylls (Hoskins and Cross, 1943;Baxter, 1950;Stein et al, 1984), whereas those with affinity to Noeggerathiales (the freesporing sister clade to the seed plants; Wang et al, 2021) exhibit alternately arranged sporophylls (Leary, 1973;Leary and Pfefferkorn, 1977;Gao and Zodrow, 1990). Others, such as the rare Tetraphyllostrobus Gao et Zodrow, which has been described as exhibiting decussate sporophyll arrangement (Gao and Zodrow, 1990), are enigmatic and do not conform to the architecture of any Paleozoic plant group (Friis, 1992). As more taxa are described, especially with associated or in situ spores (Libertín et al, 2014(Libertín et al, , 2021, a clearer understanding of the diversity of late Paleozoic strobilus structures comes into view.…”