SIEVE‐ELEMENT PLASTIDS, PHLOEM PROTEIN, AND EVOLUTION OF FLOWERING PLANTS: III. MAGNOLIIDAE

Abstract

SummaryTwo hundred sixty‐three species of the Magnoliidae distributed over the main genera of all its families were investigated with the TEM for ultrastructural characters from their sieve elements. Details from sieve‐element plastids (overall diameter, as well as qualitative and quantitative measurements of their starch and protein contents) provided the main data set for a putative phylogenetic arrangement of the families of Magnoliiflorae. The recording of the presence or absence of non‐dispersive protein bodies and nacreous wall thickenings yielded additional information.Within the Magnoliiflorae sieve‐element plastids are proposed to have evolved from large‐sized S‐type plastids with high amount of starch to small‐sized, starch‐deficient P‐type or, at the other extreme, to So‐plastids. Along this line a basic group containing Austrobaileyaceae, Illiciaceae, Schisandraceae, Chloranthaceae, Myristicaceae, and Winteraceae is distinguished from four parallel and slightly advanced groups, the Annona‐, Aristolochia‐, Magnolia‐, and Monimia‐groups.The Aristolochia‐group is held to represent one of the core groups of the Magnoliiflorae, incorporating the whole range of the different plastid forms from S‐type to So‐plastids or by several steps to form‐Pc and the monocotyledon form‐P2c plastids. Among the remaining five the Monimia‐group, only, shows a comparably broad range, while all other taxa are confined to one or two plastid forms (i.e., S‐type and/or form‐Psc resp. ‐Pcs plastids).