Rhizomes and stipe bases of dennstaedtiaceous ferns occur within a rich assemblage of permineralized plant fossils in the Upper Cretaceous Horseshoe Canyon Formation of southern Alberta, Canada. Two dennstaedtiaceous species are represented by procumbent rhizomes that branch frequently and produce closely spaced fronds. The dorsiventral rhizomes produce fronds from the top and sides and produce adventitious roots from the lower surface. Both species are assigned to the morphogenus Microlepiopsis gen. nov. on the basis of distinctive solenostelic rhizomes, with sclerenchymatous pith and cortex and relatively simple frond trace anatomy. In one species, Microlepiopsis bramanii sp. nov., the trace diverges as two $$\textsf{U}$$‐shaped bundles that unite distally to form a $$\textsf{W}$$‐shaped trace at the base of the stipe. The other species, Microlepiopsis aulenbackii sp. nov., displays a $$\textsf{C}$$‐shaped trace that diverges as a single bundle. These species show anatomical heterogeneity among dennstaedtiaceous ferns by the Campanian stage of the Upper Cretaceous and establish a minimum age of 75 million years for the clade that includes Dennstaedtia and Microlepia. Therefore, filicalean diversification at the dennstaedtiaceous grade was well underway before the end of the Mesozoic.