82 morphology of the angiosperms 



Phylogeny of the Inflorescence 



Different views have been held as to the basic phylogeny of the in- 

 florescence: that the solitary flower is primitive and the inflorescences 

 are buflt up by the addition of flowers from stems below the original 

 flower; that the large compound inflorescence is primitive and that the 

 simpler types and the solitary flower have been derived from this by 

 reduction; and that both these conditions were present in the ancestral 

 stock. 



The theory that the solitary flower represents the primitive condition 

 is largely based on the presence of the solitary flower in certain woody 

 genera now known to possess many other primitive features — Magnolia, 

 Eupomatia, Degeneria, Cahjcanthiis, Dillenia, Hhnantandra. In support 

 of the theory that the panicle is the primitive flower-bearing form 

 are the dominance of paniculate inflorescences in woody plants in 

 general; the presence of panicles in herbaceous families considered 

 fairly primitive — Ranunculaceae, Rosaceae, Liliaceae; the prevalence 

 of reduction series that lead to solitary flowers throughout angiosperms; 

 and evidence that at least some of the flowers considered examples 

 of primitive flower position are really surviving members of an in- 

 florescence. 



Within inflorescences, the racemose type has frequently been con- 

 sidered the more primitive, doubtless because development in this type 

 is chiefly acropetal, like that of vegetative stems. But flower develop- 

 ment limits apical growth, and the determinate condition in itself would 

 seem to be primitive. The solitary flower — such as that of Magnolia — 

 which seems to be primitive is determinate, and the majority of large 

 much-branched inflorescences are at least in part determinate. No clear 

 line can be drawn between determinate and indeterminate types; in 

 many genera scattered throughout angiosperms, the racemes have a 

 terminal flower and the acropetal sequence in development may be 

 upset. The racemose arrangement may well be secondary. Changes in 

 the normal ontogenetic sequence that are obviously secondary are the 

 centrifugal development within Hie androecium and the basipetal de- 

 velopment of inflorescences in some palms. The determinate inflores- 

 cence seems to be the primitive type. 



Evidence is strong that the solitary flowers, which some consider rep- 

 resent the primitive type of flower arrangement, are, in reality, examples 

 of reduction from inflorescences. Part of the basis for the citation of 

 the Magnolia flower as primitively solitary is the general acceptance of 

 this genus as one of the most primitive living angiosperms. But the 

 closely related genus, Michelia, has clusters of large flowers, and 

 Raimondea, in the related Annonaceae, has some flowers in cymes (Fig. 



