PSEUDODIPLOSTEMONY, AND ITS IMPLICATIONS FOR THE EVOLUTION OF THE ANDROECIUM IN THE CARYOPHYLLACEAE

The androecium of the Caryophyllaceae is varied, ranging from a two-wh orled condition to a single stamen. A number of species belonging to t he three subfamilies, Caryophylloideae, Alsinoideae and Paronychioidea e have been studied ontogenetically with the SEM to understand their p eculiar androecial development in the broader context of the Caryophyl lales alliance. Although patterns of initiation are highly variable am ong species, there are three ontogenetic modes of stamen initiation: a ll stamens simultaneous within a whorl, the antepetalous stamens simul taneous and the antesepalous sequentially with a reversed direction, o r both whorls sequentially with or without a reversed direction. The m ost common floral (ontogenetic) sequence of the Caryophyllaceae runs a s follows: five sepals (in a 2/5 sequence), the stamens in front of th e three inner sepals successively, stamens opposite the two outermost sepals, five antepetalous stamens (simultaneously or in a reversed spi ral superimposed on the spiral of the antesepalous stamens), five oute r sterile (petaloid) organs arising before, simultaneously or after th e antesepalous stamens, often by the division of common primordia. A c omparison with the floral configurations of the Phytolaccaceae and Mol luginaceae indicates that the outer petaline whorl of the Caryophyllac eae corresponds positionally to the alternisepalous stamens of some Ph ytolacca, such as P. dodecandra. The difference with P. dodecandra lie s in the fact that an extra inner or outer whorl is formed in the Cary ophyllaceae, in alternation with the sepals. A comparable arrangement exists in the Molluginaceae, though the initiation of stamens is centr ifugal. A comparison of floral ontogenies and the presence of reductio n series in the Caryophyllaceae support the idea that the pentamerous arrangement is derived from a trimerous prototype. Petals correspond t o sterilized stamens and are comparable to two stamen pairs opposite t he outer sepals and a single stamen alternating with the third and fif th sepals. Petals are often in a state of reduction;they may be confus ed with staminodes and they often arise from common stamenpetal primor dia. The antesepalous stamen whorl represents an amalgamation of two w horls: initiation is reversed with the stamens opposite the fourth and fifth formed sepals arising before the other, while the stamens oppos ite the first and second formed sepals are frequently reduced or lost. Reductive trends are correlated with the mode of initiation of the an droecium, as well as changes in the number of carpels, and affect the antesepalous and antepetalous whorls in different proportions, it is c oncluded that the androecium of the Caryophyllaceae is pseudodiplostem onous and is not comparable to diplostemonous forms in the Dilleniidae and Rosidae. The basic floral formula of Caryophyllaceae is as follow s: sepals 5 - petals 5 (sterile stamens) - antesepalous stamens 3+2-an tepetalous stamens 5 - gynoecium 5.