DIFFERENT WAYS TO BUILD SUCCULENT LEAVES IN PORTULACINEAE (CARYOPHYLLALES)

Species of the suborder Portulacineae (Caryophyllales) often possess succulent leaves with wide morphological diversity, including flat and terete leaves. Terete leaves are described as not developing a marginal meristem during their growth, but in Portulacineae little is known about anatomical development in this particular leaf type. To better understand the mechanisms underlying the development of different leaf morphologies within this group, we examined leaf histogenesis in species of four families with succulent leaves-Basellaceae, Didiereaceae, Portulacaceae, and Talinaceae-through optical microscopy. We observed two morphological patterns (terete and flat leaves) and three developmental patterns regarding blastozone positioning. While species with flat leaves always show the expected pattern of marginal blastozone activity, terete leaves of Didiereaceae present marginal blastozones for only a very brief period. On the other hand, terete leaves of Portulacaceae show a persistent peripheral blastozone enveloping the entire leaf during its development. We also demonstrate anatomical evidence suggesting that the terete leaves of Portulacaceae are adaxialized, i.e., their entire surface is homologous to the adaxial side, while terete leaves of Didiereaceae seem to result from a less severe modification.