Why does the architectural arrangement of flowers vary among species?

Angiosperms exhibit great variations within the architectural arrangements of their floral displays, which serve reproductive functions. The influence of display size and of individual floral traits on fitness is well understood. However, few studies have asked ‘Why does the three-dimensional arrangement of flowers within floral displays vary greatly among species?’

Digitalis purpurea
Digitalis purpurea inflorescences naturally displaying flowers either (A) 180° (on left) or (B) 360° around the flowering stalk. The latter occurs rarely in this species.

Jordan et al. examine the effect of secund (i.e., one-sided) floral displays on pollinator behaviour and find that secund inflorescences enhance bees’ tendency to move upwards between flowers, compared to control inflorescences. The authors suggest that the resulting altered pollinator behaviour has far-reaching repercussions for pollen movement (i.e. plant mating), and thereby is a key influence on the evolution of individual flowers and their overall display structures.

Reference List

Crispin Y. Jordan, Marc Natta, Lawrence D. Harder, 2016, 'Flower orientation influences the consistency of bumblebee movement within inflorescences', Annals of Botany, vol. 118, no. 3, pp. 523-527 http://dx.doi.org/10.1093/aob/mcw132