## 1 Introduction  
Floral scents are crucial volatile organic compounds (VOCs) in plants. They are used in defense mechanisms, as well as to attract pollinators and seed dispersers [1]. Additionally, their economic value for crop quality and their widespread use in the perfume, cosmetics, food, drink, and pharmaceutical industries are significant [2]. VOCs are lipophilic and characterized by low molecular weights and high melting points [3]. The biosynthesis of VOCs occurs in almost all plant organs, including seeds, leaves, fruits, and flowers [4].  
During the past decades, numerous studies have been conducted to improve our understanding of floral scents, revealing the volatile compounds of flowering horticultural plants. Floral scent, a crucial trait of flowers, has been widely characterized in ornamental plants. The scent compounds of lily cultivars (_Lilium_ spp.) are mainly three monotereponoids and one benzenoid [5]. The major components of 30 herbaceous peony (_Paeconia_ spp.) cultivars areitronello, phenyl ethyl alcohol, beta-caryophyllene, nerol, and linalool [6]. Different species of orchids exhibit distinct differences in emitted volatiles. The aroma volatiles of _Zygopentatum_ are rich in benzenoids [7], _Cymbidium_ is enriched in cineole, isoeugenol, and (-) selienne [8], and _Phalaneopsis_ mainly contains monoterepenes [9]. In jasmine (_Jasminumspp.) flowers, monoterepenes and sesquiterpenes are the major components [7]. However, there are still few reports on the floral scent of calamondin.  
Calamondin (_Citrus \(\times\) microcarpa_) has significant ornamental and essential oil application value, with its floral scent being one of its crucial ornamental traits. However, current research on calamondin primarily focuses on essential oil extraction and analysis. Research on _Citrus_ aroma compounds has focused on the essential oils of leaves, peels, fruits, and seeds, which have been popular for decades due to their medicinal uses and anti-protozoan effects. The essential oils from citrus leaves, flowers, and fruit peels are useful in aroma-matherapy for their antioxidant and antibacterial properties [10; 11; 12; 13]. The essential oils from the leaves of _Citrus hystrix_, _C. limon_, _C. pyriformis_, and _C. microcarpa_ are mainly comprised of monoterpene and sesquiterpene hydrocarbons, oxygenated monoterepenes, and sesquiterpenes, which provide essential oils with excellent antioxidant potential [14; 15; 16; 17; 18; 19]. Furthermore, the essential oils and extracts of flowers from calamondin and its related species also possess significant compound diversity and application value. For example, calamondin flower oil is dominated by monoterepenes, with limonene as the major component, while calamondin leaf oil is dominated by sesquiterpenes, with elemol as a major component. Both oils have microbial inhibitory functions [20]. The aqueous extract of _Citrus aurantium_ flowers affects uterine contraction [21]. The essential oil of _Citrus aurantium_ L. var. _amara_ Engl. flowers is also used to process scented tea [22]. However, the floral scent of calamondin has not been well understood, limiting its ornamental quality applications and improvement.  
Therefore, analyzing the floral scent components and release patterns of calamondin has important reference significance for its ornamental applications and cultivar improvement. Additionally, uncovering the volatile compounds of calamondin flowers is beneficial for better understanding the mechanisms of floral development. Our study detected the floral scent patterns of calamondin flowers across four developmental stages using HS-SPME-GC-MS. We quantified and qualified the main fragrance components at these four stages and analyzed the specific and common chemicals present. This study uncovers the pattern of calamondin's floral scent and provides a basis for potential aroma utilization and genetic improvement of ornamental varieties.