The Netherlands) connected to Deuterium-Halogen DH-2000 lamp
(DT-MINI-GS-2; Ocean Optics). Reflectance was measured as the
proportion of a standard white reference tile (WS-1-SS; Ocean
Optics). We used a coaxial fiber cable (QR-400-7-UV-VIS-BX; Ocean
Optics) for all measurements and held the distance between the
sample and the measuring probe constant. The angle of illumination
and reflection was fixed at 45◦. Data were processed with
Spectrasuite software (version 1.0; Ocean Optics) and calculated
in 5-nm-wide spectral intervals over the range of 300–700 nm.
The three types of petals were measured separately on the side
naturally exposed to pollinator vision (adaxial side of the dorsal
petal, and abaxial side of lateral and ventral petals). All measurements
were taken five times on the same section of the petal
(middle part) for each individual, and the averages of these measurements
were used to estimate the reflectance graph for each
species. We measured between 5 and 10 petals for each species
collected from different individual plants. Overall, 19 species were
analyzed, including all four putatively bird-pollinated species, five
yellow bee-pollinated species that do not change color, and 10 beepollinated
yellow/cream species that change color after anthesis
(measured both before and after the color change) (Table S1). The
species included represent all postchange flower colors reported
in this group, except pink and brown, which were not available for
this study.