Floral morphology and structure of Emblingia calceoliflora (Emblingiaceae, Brassicales): questions and answers

Emblingia calceoliflora, the sole species of the family Emblingiaceae (Brassicales), is a creeping shrub endemic to South Western Australia. The flowers have a characteristic slipper-like corolla (calceolus). Earlier studies using dry specimens have left some questions regarding the flower unresolved. Here I present an anatomical study of fresh flowers to resolve these questions. The flowers are pedicellate, strongly monosymmetric, and pentamerous with the median sepal in the abaxial position. During flower development, a pedicel turns clockwise or anticlockwise, placing the adaxial calceolus (comprising both petals) downward and a transversely dilated androgynophore upward with a large tunnel-like space between them. Two short longitudinal walls develop from the basal part of the petals, enclosing a nectary gland deep in the flower. The vascular anatomy of the androgynophore shows that lateral dédoublement occurs in five stamens, resulting in two pairs of fertile stamens on the adaxial side and (three to) six staminodes as the “hood” on the opposite side. Androecial configuration is obhaplostemony, and the gynoecium is tricarpellate/trilocular. Comparisons with flowers of other Brassicales show that an extrastaminal nectary is a synapomorphy of the core Brassicales including Emblingiaceae. The flower of Emblingia is highly specialized for adaptation to insect-pollination.