Myriad of hues make flowers one of the most vibrant creations of nature. Color of flower is a perception rendered by interaction of sunlight on its petals and limited by spectral sensitivity of the observer. Whilst human spectral sensitivity ranges from violet (400 nanometers) to red (700 nanometers), certain pollinators are sensitive to ultraviolet (320-400 nanometers) too. Flower color, with its physical basis is a potential attribute that can be used to characterize an ecosystem. Sensitivity of flowers to subtle variation in ambient environment complements the utility of its color as characterizing feature.
Color is numerically represented using 3-dimensional model as Hue (dominant color), Value (lightness) and Chroma (strength). The authors compare distribution of Hue and Saturation (Chroma) of flower of Tropical and sub-arctic regions. Floral spectral reflectance of 105 flowers belonging to as many species, spread across 38 Families were measured during February-March 2016 at Trivandrum using ASD Field Spec® spectrometer. Floral spectral reflectance of 105 flowers belonging to 26 families in Norway were downloaded from The Floral Reflectance Database (Arnold et al, 2010). Average reflectance in red, yellow, green and blue regions were aggregated as mean reflectance from 400 to 475 nanometer (blue), 476 to 550 nanometer (green), 551 to 625 nanometer (yellow), 626 to 700 nanometer (red) respectively. Whilst corresponding intensity and saturation were determined using standard transformation equations (Chien and Tseng, 2011); hue were computed using improved method and variability in color of 105 flowers were estimated using segment classification method (Smith, 2014).
The distribution of Hue and saturation values of flowers are depicted in Figure 1a & b. Absence of mode for hue indicates distinctness of flower color at each location. Whereas clustering of floral hue is pronounced in sub-arctic region, the floral hue of Trivandrum were widely scattered. Flowers that visually appeared very similar had distinctly different intensity, hue and saturation values. The mean hue of 57.730 observed indicates predominance of yellow-red colored flowers at Trivandrum. 44.76% flowers had yellow-red hue. The highest and lowest hues; 359.50 and 1.60 were observed in Centrosema pubescens flower and Bougainvillea bracts. The red hue of Bougainvillea bract is due to the presence of Betalain pigments (Lee and Gould, 2002). Comparable reflectance across all the primary colors render Jasminum sambac flowers white. However it has an yellow hue (85.10). The mean hue of 61.870 indicates a prominent yellow hue among Norwegian flowers. 43.8% of the studied flowers had yellow hue. The maximum and minimum hue value observed at sub-arctic region were 359.660 (Trifolium pretens) and 1.020 (Silene acaulis).
Temporal and physiographic distribution of flower colors are important to describe an ecosystem. It can effectively be used to characterize landscapes. This finding will complement and converge to standardize a quantitative approach to characterize landscapes using floral spectral reflectance.