the androecium 107 



Ontogeny of the Androecium 



The stamens commonly develop in acropetal, that is, centripetal, 

 sequence. The existence of basipetal, or centrifugal, sequence in the 

 androecium in several taxa was noted as early as 1871 but received 

 little attention. Recently, centrifugal sequence in the androecium has 

 been emphasized as probably an important character in the determina- 

 tion of phylogenetic relationships between families and orders. In many 

 families, order of origin and maturation is not on record; it is con- 

 spicuous in taxa with massive, spiral, multiorgan androecia; in families 

 with few stamens, it is difficult to determine. A sequence is present 

 within fascicles in the Hypericaceae and Dilleniaceae. Undoubtedly, 

 centrifugal development was derived from centripetal, the normal acro- 

 petal sequence. Centrifugal development is known in the following 

 multistaminate families and will doubtless be found in others — Actini- 

 diaceae, Aizoaceae, Bixaceae, Cactaceae, Capparidaceae, Dilleniaceae, 

 Hypericaceae, Loasaceae, Lecythidaceae, Malvaceae, Paeoniaceae, Thea- 

 ceae; it is unknown in the monocotyledons. The major many-stamen 

 families with centripetal stamens are Annonaceae, Lauraceae, Legum- 

 inosae, Lythraceae, Magnoliaceae, Myrtaceae, Nymphaeaceae, Papa- 

 veraceae, Punicaceae, Ranunculaceae, Rosaceae. The Geraniales and 

 Centrospermae have been considered probably "referable to the cen- 

 trifugal series," and, certainly, if the Capparidaceae belong in this 

 group, so must their close relative, the Cruciferae. Examples of the 

 value of sequence of development in determination of relationships can 

 be seen in its use as an important character in the removal of Paeonia 

 from the Ranunculaceae and the establishment of the Paeoniaceae as a 

 member of the Dilleniales; and in the transfer of the Crossosomataceae 

 from the Rosales to the Dilleniales. 



Centrifugal development seems to characterize certain groups of 

 families commonly recognized as related and is apparently an important 

 character in confirming supposed relationships and in suggesting others. 

 But this does not mean that all taxa with centrifugal stamens belong 

 in the same phylogenetic line; reversal of sequence of development 

 has doubtless appeared more than once, as have all other advanced 

 floral characters. Similar departure from normal sequence in develop- 

 ment is seen in the inflorescences of some palms (Carijota), where the 

 inflorescences appear successively down the trunk, and in some cauli- 

 florous tropical taxa. Centrifugal sequence in flowering is occasionally 

 seen in inflorescences — Vallisneria (staminate), Dipsaciis (proximal 

 part). This sequence in inflorescences may be apparent only — the result 

 of the condensation of large complex inflorescences. 



