The Structure and Affinities of Paeonia

Abstract

The affinities of Paeonia have been discussed by many authors from various points of view. Although the genus is included into Ranunculaceae by most authors some (HALLIER, LANGLET) regarded it as a member of Berberidaceae, while others (BARTLING, WORSDELL, HEINTZE) as a representative of a distinct family Paeoniaceae rather near Magnoliaceae.
In his histological studies of the vegetative organs of Ranunculaceae and Berberidaceae, the writer came to the conclusion that Paeonia is quite unique in the following histological structures:
1. Occurrence of the secondary ray tissue. In the aerial stems of some Ranunculaceous Species, the thickening growth often occurs, producing the secondary ray tissue in the wood as in Clematis. The secondary ray of Clematis appears only in the secondary xylem lately produced, accompanied with the lateral expansion of the xylem strand caused by the cambial activity, while that of Paconia both in herbaceous and woody species, is appearing quite closely from the innermost part of the secondary xylem. In these two genera the origin of the tissue is not the same, and the tissue of the later type never occurs neither in Ranunculaceous genera nor even in Berberidaceous ones including shrubs such as Berberis, Mahonia, etc. Therefore the existence of the tissue of this type seems, to the writer, to be of phylogenetic significance.
2. Scalariform perforation of the vessel. The families belonging Ranales of ENGLER may be divided into two groups in respect of the perforation of vessels, i.e. the first group, in which vessels have always simple perforations-Nymphaeaceae, Ceratophyllaceae, Lardizabalaceae, Ranunculaceae, Berberidaceae, Menispermaceae, Calycanthaceae, Lactoridaceae, Himantandraceae, Anonaceae and Eupomataceae, -and the second group, in which vessels have always scalariform perforations, or have usually simple ones with occasional scalariform ones-Euptelaeaceae, Cercidiphyllaceae, Magnoliaceae, Myristicaceae, Gomortegaceae, Monimiaceae, Lauraceae and Hernandiaceae. As already described hitherto by various authors, Paeonia has the vessels with scalariform perforations, and never with simple ones, while all Ranunculaceous or Berberidaceous genera show no tendencies to be scalariform. Therefore, Ranunculaceae themselves may belong to the first group, and it seems to the writer most unreasonable that the genus now mentioned is included into the family.
From the histological characteristics above mentioned which were considered by the writer as phylogenetically significant, Paeonia can be decidedly distinguished from the genera of Ranunculaceae or of Berberidaceae. Thus the writer supports the view expressed by a few authors that Paeonia belongs neither to Ranunculaceae nor to Berberidaceae, and rather may represent a distinct family Paeoniaceae, which have closer affinities to Magnoliaceae than to Ranunculaceae or to Berberidaceae.