Polymery and nectary chambers in Codon (Codonaceae): Flower and fruit development in a small, capsule-bearing family of Boraginales

Abstract

Flower and fruit ontogeny in both species of Codon D. Royen (Codonaceae) has been investigated. Morphological differences and similarities between the Hydrophyllaceae I and II (Nameae) (Wigandia Kunth), as well as the Boraginaceae s.str. and Wellstediaceae are discussed. Flowers and fruits representing different ontogenetic stages were collected from culture and observed by scanning electron microscopy and light microscopy. The polymerous calyx, corolla and androecium develop acropetally. Sepals and stamens arise in two steps: after initiation of the first half in a 2/5-spiral, the second half arises subsimultaneously. Petals and stamens arrange later on in zigzag order to form two pseudowhorls and usually differ in size. In the mature stage, the gynoecium is nearly completely superior and symmetrical. Nectar compartments are formed by partitioning septa developing between filaments and corolla tube. They are covered by trichomes and laterally broadened filaments and present nectar from a nectary at the base of the gynoecium. This nectary formation leading to a revolver flower is unique in Boraginales. Our results indicate that Codonaceae share similarities with Wellstediaceae (Boraginales I) and Hydrophyllaceae I and II (Boraginales II). They are similar in gynoecium and fruit ontogeny and morphology, but differ dramatically in flower morphology. Especially polymery and the formation of nectary chambers are unique to these plants within the Boraginales and support their treatment as a separate family.