Well preserved assemblages of plant microfossils have been recovered from Lower Carboniferous sediments - principally or entirely marine in origin and Visean in age encountered in four boreholes in the landward Bonaparte Gulf Basin of Western Australia and Northern Territory. The sediments are representative of the following lithostratigraphic units: Bonaparte Beds (upper portion) and overlying Tanmurra Formation (intersected by Bonaparte Nos 1 and 2 Wells, central basinal province of Bonaparte Gulf Basin, Western Australia); Milligans Beds (Spirit Hill No. 1 Well; Spirit Hill and Milligans No. 1 Bores, all located in the southeastern platform region of the basin, Northern Territory) and overlying Burvill Beds (basal portion) of Milligans No. 1 only. The 55 species of plant microfossils recognized are distributed among 32 genera of trilete sporae dispersae, including one new genus, Exallospora, which is instituted for the reception of distally annulate cingulate forms having typically verrucate sculptural elevations. Twenty-two species are referable (six tentatively so) to previously established taxa. The palynological flora is dominated by the pan-Australian, Famennian to ?mid-Carboniferous species Granulatisporites frustulentus Balme, Hassell (emended herein), which accounts for 44-83 percent of the spore populations. Certain (inevitably subordinate) spore forms, either the same as or closely similar to species known from northern hemisphere Lower Carboniferous sediments, lend confirmation to the Visean age previously adduced from the contained fauna.