Micromorphological evidence for androecium origin of Claytonia (Montiaceae) petaloids

Abstract

Caryophyllales is an order distinguished for having flowers with only one perianth whorl - the perigone. The perigone is a calyx derived structure that can have either petaloid or sepaloid appearance. Members of the Portulacinae suborder have tendency to have a false bipartite perianth, forming a petaloid perigone and an epicalyx with the subtending bracts of the flower. Although Claytonia belongs to the Portulacinae suborder, previous studies have suggested a different origin for its petaloid organs other than the sepals. In this study we investigated the floral development of Claytonia sibirica and Claytonia perfoliata using Scanning Electron Microscopy (SEM) to understand the origin of the petaloid organs in the genus. Our results show that petaloid organs in Claytonia are of androecium origin and can be interpreted as the expression of the typical Caryophyllales' perigone growing in androecium tissue.