RANALES 421 



scalariform vessels. But they have advanced characters: flowers that 

 show transitions from bisexual to unisexual; polyporate pollen; soli- 

 tary carpels; and septate wood fibers, which replace parenchyma. This 

 family is an excellent example of the mixture of primitive and ad- 

 vanced characters found in most ranalian families. 



Discussion and Summary of the Ranales 



In the twentieth century, the increasing acceptance of the Ranales 

 as the most primitive living dicotyledons has stimulated critical mor- 

 phological study throughout the order. The studies have been broad, 

 with conclusions based on evidence from many fields. The value of 

 palynology and the anatomy of wood in phylogenetic comparisons has 

 been recognized. Doubtless, no other major taxon in the angiosperms 

 is now so well known, structurally. 



Phylogenetically, the Ranales now appear as a somewhat heteroge- 

 neous group, held together loosely by the possession of several primi- 

 tive characters. Relationships within the order are difficult to deter- 

 mine; the families seem to be an assortment of relic types, representing 

 several ancient lines rather than a single basic stock (Fig. 147). Archaic 

 characters have been retained but are combined with well, even 

 highly, advanced structure — for example, unsealed, stipitate, styleless 

 carpels and vesselless xylem are associated with unisexuality and syn- 

 carpy ( Winteraceae ) ; laminar stamens with solitary carpels (Degen- 

 eriaceae); beetle pollination and the most primitive scalariform vessel 

 elements with connation of carpels, perigyny, and multilacunar nodes 

 (Eupomatiaceae). Obviously, these most primitive angiosperms are 

 highly specialized in some characters (evidence supporting the view 

 that the flowering plants are very old). Living angiosperms with all 

 characters primitive are not to be expected. 



The Plant Body. The Ranales strongly support the view that the arbo- 

 rescent habit is primitive in angiosperms, for it appears in correlation 

 with primitive characters in nodal structure, xylem, phloem, pollen, 

 ovule, nucellus, archesporial tissue. The herbaceous taxa have the ad- 

 vanced characters: trilacunar or multilacunar nodes, simply perforate 

 vessel elements, libriform and septate fibers, tricolpate pollen. The 

 dominance in the Ranales of the simple, pinnately veined leaf is strong 

 evidence that this is a primitive leaf type in the angiosperms. Large and 

 palmate leaves are restricted chiefly to the herbaceous Ranunculaceae. 

 (The simple leaves of Tetiacentron and Cercidiphijllum are palmately 

 veined. ) The Ranales lend no support to the view — a part of the durian 

 theory of the nature of the plant body of primitive angiosperms — that 

 the primitive angiosperm leaf was large and pinnately compound. Fur- 

 ther, the freely branching, arborescent members of this order show no 



