Intraspecific variation and palaeogeographic dispersal of the Mississippian miosporeReticulatisporites magnidictyusPlayford & Helby, 1968

Abstract

Renewed study of an Australian Mississippian-age palynoflorathe Grandispora maculosa zonal assemblage from the Mount Johnstone/Italia Road Formation (Hunter Valley, New South Wales)reveals significant morphological variation in some of its key miospore componentsin particular Reticulatisporites magnidictyus, the subject of the present account. Detailed microscopy of numerous topotypic specimens of this species, originally described in 1968, results in its formal emendation; this takes particular account of the hitherto unrecognised presence of a proximo-apical prominence about the confluence of the laesurae. The G. maculosa palynoflora, with its constituent R. magnidictyus, has been reported from within a ca. 30-45 S palaeolatitudinal belt, at numerous Western, Eastern, and Northern Gondwanan locations in strata of middle Visean-early Serpukhovian age, but with a possible extension into the Early Pennsylvanian (Bashkirian). Consequently, R. magnidictyus is one of a very limited group of distinctive miospore species that facilitate long-distance chronostratigraphic correlation within the supercontinent.