Sieve‐Element Plastids, Nuclear Crystals and Phloem Proteins in the Zingiberales

Abstract The sieve‐element characters of 40 species from all families making up the monocotyledon order Zingiberales have been studied by transmission electron microscopy. While phloem‐proteins are a typical component of all eight families, the Zingiberaceae are characterized by nondispersive protein bodies derived from nuclear crystals. The sieve‐element plastids are of the form‐P2cs, i.e. contain cuneate protein crystals (as typical of all monocotyledons) and starch grains, those of the family Musaceae have protein filaments in addition (form‐P2cfs). The exclusiveness of the form‐P2c(f)s plastids contributed to the homogeneity of the order and its distinctness among other monocotyledon taxa. When diameters of the sieve‐element plastids from leaf phloem are compared, in the “banana group” the family averages of the Strelitziaceae and the Lowiaceae have, respectively, maximum and minimum values and are clearly different from those in the Musaceae, the family in which they have been included previously. In the “ginger group”, the family averages of the Zingiberaceae, Costaceae, and Marantaceae are close to the order average, with only Cannaceae having minimum values. A comparison of species averages, however, reduces the size differences between families: the value for Ravenala (Strelitziaceae) is close to those of the five Musaceae tested, and that of Globba (Zingiberaceae) even slightly lower than the species average of Canna .