Core material from an exploratory diamond drillhole (DDH CL5) in the Irwin Terrace, northern Perth Basin, Western Australia, contains a profuse and well-preserved palynofloral assemblage composed almost exclusively of trilete miospores. These comprise at least 32 species, distributed among 23 genera. Two species – Retusotriletes separatus sp. nov. and Apiculiretusispora tersa sp. nov. – are new, and Velamisporites cortaderensis (Césari & Limarino, 1987) is proposed as a new binomial combination. The palynoflora essentially replicates compositionally the Grandispora maculosa Assemblage, first described in 1968 from New South Wales (Italia Road Formation of the Southern New England Orogen) with revised dating of late Visean. Particularly noteworthy in both local and regional biostratigraphical contexts is the combined presence of G. maculosa, Reticulatisporites magnidictyus, Cordylosporites asperidictyus, Foveosporites pellucidus, Indotriradites kuttungensis, I. daemonii, Verrucosisporites aspratilis, V. gregatus, V. quasigobbettii, Raistrickia accinta, R. radiosa, Diatomozonotriletes daedalus and Psomospora detecta. Of these, V. quasigobbettii and I. kuttungensis are predominant. Additionally, the assemblage contains some trilete species reported subsequently (in 1992) from a slightly younger (Pennsylvanian) succession of the Galilee Basin, southern Queensland; e.g. Cyclogranisporites firmus, Verrucosisporites basiliscutis, Dibolisporites disfacies, Diatomozonotriletes birkheadensis, Densoisporites truswelliae (syn. Densoisporites sp. of Jones & Truswell), Grandispora (Spelaeotriletes) queenslandensis and Velamisporites cortaderensis (syn., inter alia, Reticulatisporites bifrons Jones & Truswell). Significantly, however, the CL5 palynoflora is devoid of gymnospermous prepollen (indeed any pollen grains) that have been documented from the Galillee Basin deposits. Many components of the G. maculosa suite have been reported from elsewhere in Gondwana, particularly Brazil and Argentina, attesting to its stratigraphical significance across the supercontinent, and to the widespread dispersal of its pteridophytic parental flora in a relatively narrow time interval, bracketed within the late Visean through early Serpukhovian. The present assemblage, and indeed its representatives elsewhere in Gondwana, was likely deposited in non-marine, fluvial or lacustrine, interglacial environments that preceded the extensive icehouse conditions that prevailed during much of the Pennsylvanian.