434 MORPHOLOGY OF THE ANGIOSPERMS 



as do the stamens (Fig. 46). The disc perhaps corresponds, morphologi- 

 cally, to the staminodia of Eupomatia and Calycanfhtis where inner 

 staminodia are also modified as adaptations to beetle pollination. (In 

 Paeonia, the staminodia are secretory and the "food" is fluid.) 



Other characters of Paeonm supporting the removal of the Paeoniaceae 

 from the Ranales are: pollen unlike that of any of the ranalian families; 

 persistent sepals; arillate seeds; hypogeal seed germination, in contrast 

 to that of true ranalian families, which have epigeal (except in part of 

 the genus Clematis) ; petals that are, in petal-trace number, bracts in 

 Paeonia, whereas those of the Ranunculaceae are sterile stamens. 



Anatomically, Paeonia differs from its former sister genera chiefly in 

 the type of vascular bundles and wood structure. The vascular bundles 

 of ranunculaceous genera approach the amphivasal type; the xylem is 

 V-shaped in cross section, with the phloem between the arms of the 

 V. The bundles of Paeonia approach the amphicribral type; the xylem 

 is unforked, the phloem is distal and lateral, spreading and overlapping 

 the xylem. The vessels of Paeonia are scalariform. 



Differences in the traces of the floral organs also set Paeonia apart 

 from the Ranunculaceae. The sepals and petals have few to several 

 traces; in other ranalian genera, the sepals usually have three traces 

 and the petals one. A stamen-trunk system is characteristic of Paeonia. 



The vessels of Paeonia are small, solitary, and scalariform, in contrast 

 with the large, usually clustered, simple vessels of the Ranunculaceae. 

 The fibers have distinctly bordered pits, in contrast to the libriform 

 fibers of the Ranunculaceae. The phloem has little or no sclerenchyma; 

 that of the Ranunculaceae has many fibers and stone cells. Accessory, 

 cortical, vascular bundles, suggesting those of Cahjcanthus and those in 

 flowers of Magnolia, are present in Paeonia, absent in the Ranuncula- 

 ceae. The Paeoniaceae are a good example of the value, in phylogenetic 

 classification, of characters other than those commonly used in taxonomic 

 treatments. The basic number of chromosomes also sets Paeonia (five) 

 far from that of the Ranunculaceae ( seven to nine ) . 



Relationships of the Paeoniaceae have long been in question; re- 

 semblances to various ranalian families have been seen. General flower 

 structure suggests the Magnoliaceae, Annonaceae, and Calycanthaceae. 

 The concave receptacle, cortical bundles in the stem, beetle pollina- 

 tion, and especially the peculiar staminal disc, make resemblance to the 

 Calycanthaceae, perhaps, the strongest. Resemblance has been seen in 

 leaf form to Hydrastis, Actaea, and Cimicifuga and, in habit of the 

 herbaceous species, to Podophijllum and other berberidaceous genera. 

 But the Paeoniaceae clearly belong in the Dilleniales, though doubtfully 

 near the Crossosomataceae, as has been suggested. The wood of Crosso- 

 soma, with its simply perforate vessels, is unlike that of Paeonia. All 



