The new species Malmidea aptrootiana is described from the Dominican Republic. It forms part of the M. granifera complex in having a verrucose thallus (medulla whitish, K+ yellow) and apothecia with a dark hypothecium and with an excipulum containing a medullary layer. Within this complex, the new taxon stands out by its comparatively large ascospores (19–27 × 10–12 μm). Only three species in this complex have larger ascospores: M. indica and M. subindica (28–40 × 12–24 μm), both described from India, and M. sorsogona (22–34 × 11–16 μm), described from the Philippines. The latter overlaps in ascospore size with the new species, but features a yellowish medulla in the verrucae and further differs in the 4-spored asci and apothecia with brownish black disc and thick, mostly entire margins (disc purplish dark brown with the margins becoming thin and crenulate in the new species). Three other species in which the ascospores can reach lengths over 20 μm are M. chrysostigma, M. fenicis, and M. verrucosa, all from the eastern Paleotropics. The first two differ in the yellow, K+ red(-violet) medulla of the verrucae, whereas M. verrucosa features 4-spored asci and apothecia with a blackish brown disc and entire, dark margins. In order to facilitate the distinction of these and other species in this group, we provide an updated world key with illustrated diagnostic features for the species of the M. granifera complex. While elaborating the key, we came across Megalospora simplex Vězda, a foliicolous lichen described from Tanzania, which turned out to belong in Malmidea, so we also propose the new combination Malmidea simplex here.