SIEVE-ELEMENT PLASTIDS, PHLOEM PROTEINS, AND THE EVOLUTION OF THE RANUNCULANAE

The sieve-element plastids of 85 species of the Ranunculanae were inve stigated by transmission electron microscopy. All contained form-Ss pl astids. The average diameter of the sieve-element plastids from stem p hloem is with 1.62 mu m rather large, both compared to other superorde rs and to the dicotyledon average. Among the five families recognized in the Ranunculales (incl. Papaverales), Lardizabalaceae and Menisperm aceae contain the largest average diameters (above 1.9 mu m) while tho se of Berberidaceae, Ranunculaceae, and Papaveraceae are about 1.5 mu m. Within the families there is considerable size variation which perm its the inclusion of segregate taxa, even if their plastid diameter is much different from the family average (e.g., Hydrastis). Nelumbo nuc ifera (Nelumbonales) contains form-Ss plastids that are very similar t o those of the Ranunculales. - Dispersive P-protein is a common featur e found in the sieve elements of all taxa studied. Nondispersive prote in bodies are recorded for Clematis and Nelumbo only.