Leaf anatomy of various groups in Macaranga (Bicolor, Denticulata, Gracilis, Javanica, Pachystemon, Pruinosae, Tanarius and Winklerianae) and Ptychopyxis (Euphorbiaceae)

The leaf anatomy of eight (generally informal) groups of Macaranga and Ptychopyxis (Euphorbiaceae, Acalyphoideae) was studied based on 79 species (plus various infraspecific taxa) represented by 123 collections. All species showed abaxial, paracytic stomata (perhaps an exception for M. javanica), a dorsiventral mesophyll, extra-floral nectaries on the leaf surfaces, collateral bundles and druse-like crystals. All Macaranga species showed disc-shaped glandular hairs, a character shared with its sister genus Mallotus, bundle sheet extensions, a generally local hypodermis and quite often papillae, present in various sizes and often concentrated around the disc-shaped glandular hairs that are sunken in cavities shielding the stomata. Some Macaranga species show fibriform sclereids, which are much more abundant in Ptychopyxis. Ptychopyxis has a much higher number of (unhidden) stomata than Macaranga and the bundle sheet extensions and hypodermis were not observed. Cuticular macerations were difficult to make in all specimens as the cuticles were very thin. Transverse sections sometimes failed, especially in Ptychopyxis, due to abaxially extending nerves and thin in between mesophyll.