The Pollen Ultrastructure of Williamsoniella coronata Thomas (Bennettitales) from the Bajocian of Yorkshire

Abstract

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Biota and palaeoenvironment of a high middle-latitude Late Triassic peat-forming ecosystem from Hopen, Svalbard archipelago

“…Such monosulcate grains from the Mesozoic were produced by Cycadales, Bennettitales, Ginkgoales and Pentoxylales (although the last of these is typically a Gondwanan group: Balme 1995). Given that the only gymnospermous macrofossils identified in the peat are attributed to Bennettitales, these relatively common pollen grains probably belong to that group, and are certainly similar to examples illustrated by Wieland (1899), Zavialova et al (2009) and Osborn & Taylor (2010) recovered from reproductive organs of that clade. However, ginkgoalean leaves are also known from adpression floras of the host formation, so derivation of the pollen from this group cannot be excluded entirely.…”

The ultrastructure of fossil dispersed monosulcate pollen from the Early Cretaceous of Transbaikalia, Russia

“…In some bennettitaleans, exine surface characters are also shown to be important for characterisation of low-rank taxa (Zavialova et al, 2009). There is a hope that as soon as more information about the surface morphology of fossil ginkgoalean pollen becomes available, it also could be used for species differentiation.…”

“…The exine ultrastructure of bennettitalean pollen grains has been studied to a lesser degree than that of fossil cycads (Taylor, 1973;Ward et al, 1989;Osborn & Taylor, 1995;Zavialova et al, 2009;Osborn & Taylor, 2010) and there are currently no unique pollen features defining the group, although all are clearly distinguished from the pollen of cycads in exine ultrastructure.…”

“…The exine ultrastructure has been studied in the pollen grains of the Jurassic cycads Cycandra profusa Krassilov, Delle et Vladimirova, 1996(Tekleva et al, 2007 and Androstrobus prisma Thomas et Harris, 1960(Zavialova & Van Konijnenburg-van Cittert, 2008 and the bennettitalean Williamsoniella coronata Thomas, 1915(Zavialova et al, 2009). As to ginkgoaleans, although several reproductive structures and in situ pollen grains have been reported (Van Konijnenburg-van Cittert, 1971;Balme, 1995;Rothwell & Holt, 1997), we have failed to extract pollen from their pollen organs.…”

Williamsonia carolinensis sp. nov. and Associated Eoginkgoites Foliage from the Upper Triassic Pekin Formation, North Carolina: Implications for Early Evolution in the Williamsoniaceae (Bennettitales)

“…Even the type of Williamsonia (viz., Williamsonia gigas [Lindley and Hutton] Carruthers) was originally described as a whole plant (Carruthers 1870). The Jurassic Williamsoniella Thomas is the only williamsoniaceous reproductive structure confidently confirmed as bisporangiate (Harris 1969;Crane and Herendeen 2009;Zavialova et al 2009;Pott and McLoughlin 2014): a central ovulate organ similar in structure to Williamsonia is surrounded by a whorl of complex microsporangiate organs-a structure similar to the elaborate forms of Cycadeoidaceae (Wieland 1906(Wieland , 1916Watson and Sincock 1992). The reproductive structures of the latter, however, seem to have never fully opened and were probably self-pollinated (Delevoryas 1968).…”