Variegation and red abaxial epidermis define the leaf optical properties of Cyclamen purpurascens

• Differences in the light- and dark-green sections disappear during growing season.
• The pigment-based differences in the leaf variegation increase during growing season.
• The red anthocyanic abaxial epidermis is important for light absorbance.
• Reduction of transmitted light might affect organisms dwelling beneath the leaves.

Cyclamen purpurascens originates from the forest understorey and has variegated leaves and red abaxial epidermis. We measured the morphological and biochemical traits, and reflectance and transmittance spectra of leaves of C. purpurascens sampled through the growing season. We determined the optical properties and differences between the light-green and dark-green sections of the variegated leaves, and investigated the role of the red abaxial epidermis. The light-green leaf sections contained lower contents of chlorophyll a and b, carotenoids (in all samples) and anthocyanins (in April only) per leaf area, compared to the dark-green leaf sections, although the ratios of chlorophyll a to b and carotenoids to total chlorophyll were the same, except in April. During the closing of the canopy, chlorophyll a and b contents increased, while contents of carotenoids and anthocyanins decreased, as did the chlorophyll a/b and carotenoid/total chlorophyll ratios. The optical properties of the leaves in February showed high reflectance for UV and violet radiation, and low reflectance for near infrared radiation, for both types of leaf sections. The transmittance spectra for leaves without the red anthocyanic epidermis showed a pronounced peak from 520 nm to 625 nm, and enhancement in the near infrared region. The relative reflectance spectra of the red and colourless abaxial epidermis alone differed only in the green and yellow range. The relative transmittance of the red abaxial epidermis was significantly lower than for the colourless epidermis over the entire spectral range. Decreased transmittance in the green and yellow was obtained only for the red coloured abaxial epidermis. The variability of transmittance spectra during the season is best explained by the levels of chlorophyll b, carotenoids and anthocyanins. Our data reveal the importance of these pigments in leaf variegation, and particularly of the red abaxial anthocyanic epidermis for absorbing light in the green, yellow and near infrared.