{'fraction_non_alphanumeric': 0.03696275071633238, 'fraction_numerical': 0.023209169054441262, 'mean_word_length': 5.029360967184801, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 1, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Is floral iridescence a biologically relevant cue in plant-pollinator signalling? A response to van der Kooi et al. (2014b).

van der Kooi et al. (2014a) presented optical analyses of the petals of six species of angiosperms. They investigated the flowers of 50 plant species (by scanning electron microscopy) and then selected four species with different surface structures (plus a further two in the Supporting Information) for optical characterization. Subsequently, van der Kooi et al. (2014b, in this issue of New Phytologist, pp. 18–20) repeated measurements of one of the species (Hibiscus trionum) and presented photographs of two of the species from their earlier paper (van der Kooi et al., 2014a), plus a further two previously unreported species. They did not record as iridescent any of the eight flowers that they optically characterized and/or photographed. By contrast, we presented optical characterization and photographs ofH. trionum (taken in the laboratory, in daylight, with no flash), which we showed to be visibly and measurably iridescent, with an associated regular surface structure termed a diffraction grating in the central part of the flower (Vignolini et al., 2014). Although the distribution of floral iridescence within the 300 000 species of angiosperms remains to be explored (Vignolini et al., 2014), this phenomenon is likely to be relatively uncommon, hence the apparent lack of records before Whitney et al.’s (2009) paper. van derKooi et al. (2014a,b) did not record floral iridescence in a sample of eight species. We are currently exploring this distribution in a phylogenetic context; so far we have identified iridescent flowers infrequently distributed across all major angiosperm groups. InH. trionum, we found the same measurable iridescence effect in the three independent lines we investigated – our laboratory stock sourced from Chiltern seeds (www.chilternseeds.co.uk), the line held by the Cambridge University Botanic Garden (maintained as selfed seed from germplasm supplied by Cluj-Napoca Botanic Garden in 1996), and a native New Zealand line grown from seed of Auckland Museum Herbarium voucher AK253689 (kindly supplied by Brian Murray). Our usual laboratory growth conditions are described in Vignolini et al. (2014), and the flower also develops well outdoors in sheltered glasshouse bays of the Cambridge University Botanic Garden (a relatively dry temperate habitat). The difference between our results and those of van der Kooi et al. (2014a,b) on this species could be due to one (or more) of several possible factors, but we currently lack details of their seed source or growth conditions to better resolve these discrepancies. (1) As they propose, they could be working with a distinct genetic lineage that lacks iridescence; the flower photographed in van der Kooi et al. (2014b) does appear morphologically distinct from our lines. (2) van der Kooi et al. (2014a,b) may lack access to fully developed specimens, since the flower of H. trionum only opens fully in optimal growth conditions. (3) There could be a temporal effect, because the flower ofH. trionum lasts for only a few hours on the plant, and the iridescent effect deteriorates rapidly when the flower wilts after removal. Whatever the explanation for the lack of iridescence recorded by van der Kooi et al. (2014a,b), the photographs and optical measurements presented in Vignolini et al. (2014) demonstrate, unequivocally, that some flowers are iridescent.