432 MORPHOLOGY OF THE ANGIOSPERMS 



advanced characters of higher orders. The Ranales have retained many 

 archaic characters, while progressing far in other characters. The 

 variety of combinations of these archaic and advanced characters — 

 almost as great as the number of families — suggests highly specialized 

 remnants of ancient stocks. No one family can be selected as the most 

 primitive. Both the Winteraceae and the Magnoliaceae have been so 

 considered, but both have advanced genera with syncarpy and uni- 

 sexuality. 



DILLENIALES 



The Dilleniales, closely resembling the Ranales in morphological 

 characters, have, in some classifications, been merged with them. The 

 orders have been held apart by the presence of fasciculate arrangement 

 of stamens in the Dilleniales (stages in development are present in the 

 Dilleniaceae and Paeoniaceae); of centrifugal sequence in stamen on- 

 togeny; of seeds with an aril (except in Paeoniaceae, where the ovule, 

 with massive integuments, is borne on placental projections); of tri- 

 colpate pollen. These distinctions are weak, because the Winteraceae 

 ( Drimys ) have recently been shown to have centrifugal stamen de- 

 velopment, and fasciculate stamens are present in the Monimiaceae and 

 Lauraceae. The fasciculate stamens of the two orders are, however, 

 apparently of somewhat different nature and of independent origin as 

 clusters. The fascicles of the ranalian taxa consist of three, or perhaps 

 five, stamens and show reduction in number by transformation into 

 nectaries; the fascicles of the Dilleniales consist of numerous stamens, 

 reduced in number in Hibbertia, but without transformation into nec- 

 taries. The seeds of peonies approach the arillate type in the massive 

 integuments and placental enlargement. A third weakness in this dis- 

 tinction between the Ranales and the Dilleniales is the presence of 

 tricolpate pollen in a few (the more advanced) ranalian families. From 

 a morphological viewpoint, the maintenance of the order Dilleniales is 

 justified. The families constituting the order — Dilleniaceae, Paeoniaceae, 

 Crossosomataceae — form a related group, well apart from the ranalian 

 families. The presence of fasciculate stamens in the Dilleniales supports 

 the theory that the order represents an ancestral stock for the Guttiferae 

 and related families. 



Dilleniaceae 



The Dilleniaceae, chiefly an Australasian family, have many of the 

 primitive characters of the Ranales. They stand apart from the Ranales 

 chiefly in their centrifugal and, in most taxa, fasciculate stamens. In 

 habit, the Dilleniaceae are trees, shrubs, vines, and, rarely, herbs. 

 Hibbertia, a large genus of about 110 species, chiefly of temperate 



