Floral morphogenesis in Camptotheca

Camptotheca is endemic to China and there are limited data about the breeding system and morphogenesis of the flowers. Camptotheca is thought to be related to Nyssa and Davidia in Nyssaceae, which has sometimes been included in Cornaceae. However, molecular phylogenetic studies confirmed the inclusion of Camptotheca in Nyssaceae and its exclusion from Cornaceae. Gong et al. reveal developmental features of the inflorescence and flowers in Camptotheca to compare with related taxa in Cornales.

SEM image of a flower
Image: Gong et al. 2018

Gong and colleagues collected inflorescences and flowers of Camptotheca acuminata at all developmental stages and examined them with a scanning electron microscope and stereo microscope.

Camptotheca has botryoids which are composed of several capitate floral units (FUs) that are initiated acropetally. On each FU, flowers are grouped in dyads that are initiated acropetally. All floral organs are initiated centripetally. Calyx lobes are restricted to five teeth. The hypanthium, with five toothed calyx lobes, is adnate to the ovary. The five petals are free and valvate. Ten stamens are inserted in two whorls around the central depression, in which the style is immersed. Three carpels are initiated independently but the ovary is syncarpous and unilocular. The ovule is unitegmic and heterotropous. Inflorescences are functionally andromonoecious varying with the position of the FUs on the inflorescence system. Flowers on the upper FU often have robust styles and fully developed ovules. Flowers on the lower FU have undeveloped styles and aborted ovules, and the flowers on the middle FU are transitional.

Camptotheca possesses several traits that unify it with NyssaMastixia and Diplopanax. Inflorescence and floral characters support a close relationship with Nyssaceae and Mastixiaceae but a distant relationship with Cornus. Their results corroborate molecular inferences and support a separate family Nyssaceae.

Further reading

Gong, J., Li, Q., Wang, X., Ma, Y., Zhang, X., Zhao, L., … Ronse De Craene, L. (2018). Floral morphology and morphogenesis in Camptotheca (Nyssaceae), and its systematic significance. Annals of Botany, 121(7), 1411–1425. https://doi.org/10.1093/aob/mcy041