Chemical Characterization of Floral Pigments and Headspace Volatiles of Cassia fistula L.

Abstract

Cassia fistula L. (Leguminosae: Caesalpinioideae), commonly known as the golden shower tree, is an ornamental species valued for its striking yellow flowers and cultural significance in tropical regions. Despite its prominence, information on the floral pigments and volatile constituents contributing to its visual and olfactory traits remains limited. This study characterised floral pigments and headspace volatile compounds using headspace gas chromatography–mass spectrometry (HS–GC–MS), liquid chromatography–mass spectrometry (LC–MS), UV–visible spectroscopy and nuclear magnetic resonance spectroscopy. HS–GC–MS tentatively identified ten volatile compounds, predominantly fatty acid derivatives. (E)-2-Hexenal and hexanal were the principal volatile constituents, while 2-hexadecanone and hexadecanoic acid were also detected at appreciable proportions in the morning sample. The major isolated floral pigment was characterised as trans-β-carotene by UV–visible, mass and ¹H and ¹³C NMR spectroscopy. LC–MS further indicated the presence of lutein, violaxanthin, neoxanthin, β-cryptoxanthin, β-zeacarotene and 4,4′-diapo-zeta-carotene. Field observations documented seven floral visitor taxa from the orders Hymenoptera, Lepidoptera and Diptera during the flowering period. The coexistence of conspicuous carotenoid pigmentation and a volatile profile dominated by green leaf volatiles suggests that visual and olfactory floral traits may jointly contribute to interactions with floral visitors. However, the observational design and tentative chemical assignments do not establish causal effects on pollinator behaviour. The findings provide a baseline chemical description of C. fistula flowers and support further replicated analyses using intact-flower volatile collection, authentic carotenoid standards and controlled behavioural assays.