Calandrinia sect. Calandrinia, C. sect. Monocosmia, and some species of C. sect. Acaules share identical leaf blade and petiolar morphology, fimbrial veins, predominantly brachytetracytic and staurocytic stomata surrounded by a cycle of subsidiary-like cells, and unicellular ribbed trichomes or papillar trichomes. Other species of C. sect. Acaules have irregularly brochidodromous venation without a fimbrial vein, predominantly brachyparacytic stomata, and/or no trichomes; venation and stomatal morphology in these species is similar to that found in Montiopsis. Leaves of Montiopsis lack petioles, have glandular or eglandular, uniseriate- and/or multiseriate-multicellular trichomes (although some examined specimens of M. subg. Dianthoideae appear to be glabrous), and generally have brachyparacytic stomata (although some examined specimens of subgenus Dianthoideae have a small proportion of brachytetracytic/staurocytic stomata with an outer cycle of cells) (...)