Unveiling the aesthetic secrets: exploring connections between genetic makeup, chemical, and environmental factors for enhancing/improving the color and fragrance/aroma of Chimonanthus praecox

Introduction

The term ‘ornamental plant’ encompasses all plants appreciated for their aesthetic appeal, including beautiful flowers or distinctive architectural features, boasts a wealth of ornamental plant resources that play a crucial role in enhancing living environments, cultivating human sentiment, and contributing to structural adjustments within the agricultural industry (Zheng et al., 2021; Francini et al., 2022). One noteworthy ornamental plant is the wintersweet (Chimonanthus praecox (L.) Link), which has developed distinctive fragrant aroma and winter-flowering properties critical for its effective sexual reproduction (Shang et al., 2020). Currently, wintersweet holds commercial importance as a potted and landscape plant, gaining popularity globally. Due to its exceptional flowering time and distinctive fragrance during the winter months, wintersweet has been introduced to various regions worldwide, including Japan, Korea, Europe, Australia, and America and is highly prized in temperate China (Sui et al., 2015; Hu et al., 2020; Huang et al., 2021). Wintersweet exhibits a primary distribution in the southern, central, eastern, southwestern, and northwestern regions of China (Chen, 2012), and has a rich history of cultivation in China, spanning over a millennium (Zhao et al., 2007; Xiang, Zhao & Chen, 2010).

Wintersweet flowers find diverse uses, from potpourri and linen scenting to essential oil extraction for cosmetics, perfumes, and aromatherapy. Additionally, wintersweet flowers are employed in herbal teas and various Chinese folk remedies for ailments ranging from coughs to measles (Lv et al., 2012). Ongoing research by various researchers focuses on uncovering the health benefits of wintersweet, attributed to its antifungal, antioxidant, and biocidal properties (Lv et al., 2012). Its popularity is attributed to its unique characteristics, including a winter blossoming period, exciting yellow blossoms, and a potent fragrance, establishing it as a favored ornamental plant (Zhao et al., 2007). The distinctive fragrance of Chimonanthus praecox has led to its widespread use in landscaping, as cut flowers, and as a material for bonsai (Lin & Chen, 2020; Meng et al., 2021). Beyond ornamental purposes, this plant holds economic significance in industries such as tea production, essential oils, and cosmetics (Lu et al., 2020). Additionally, Chimonanthus praecox is recognized for its rich content of volatile components, presenting considerable potential in drug research and development (Li, 2018; Xu et al., 2018; Shen et al., 2020).

The distinctive floral fragrance of Chimonanthus praecox originates from volatile compounds and fulfills diverse ecological and economic functions. These encompass deterring pathogens (Arimura et al., 2004) and herbivores (Pichersky & Gershenzon, 2002; Unsicker, Kunert & Gershenzon, 2009), safeguarding flowers against detrimental insects (Li et al., 2017), enticing pollinators (Dudareva, Pichersky & Gershenzon, 2004), fostering medicinal attributes (Zhao et al., 2012), enabling plant-to-plant communication (Raguso, 2008; Schiestl, 2010), elevating aesthetic appeal, and even drawing tourists (de Vega, Herrera & Dötterl, 2014), among others. These manifold roles underscore the significance of floral fragrances in both scientific research and economic considerations.

Flowering, a pivotal stage in the plant life cycle, is intricately regulated by both internal indications and a myriad of environmental factors (Noman et al., 2017; Cho, Yoon & An, 2017). Various tree species exhibit distinct seasonal patterns in their flowering. Wintersweet, characterized by its winter blooming, is particularly notable for its flowers, which emit an intense fragrance attributed to a mixture of volatile terpenoids (sesquiterpenes and monoterpenes) and benzenoids (Tian et al., 2019). These fragrant compounds are released from nectaries located on the adaxial surface of inner petals (Li et al., 2018). The essential oils derived from wintersweet flowers find widespread applications in the perfume, cosmetics, and flavor industries, owing to their unique and pleasant aroma (Deng, Song & Hu, 2004; Azuma, Totota & Asakawa, 2005). Beyond their industrial use, the floral scent serves crucial ecological functions. It plays a pivotal role in attracting and guiding pollinators, ensuring the plant’s reproductive success. Additionally, the fragrance acts as a defense mechanism, protecting the plant’s susceptible reproductive structures from pathogens and florivores (Huang et al., 2012).

Wintersweet has developed a remarkable adaptation to coordinate its blossoming with seasonal climate fluctuations, particularly responding to temperature variations. The process of flower origination begins in spring, yet the actual blooming of flowers occurs throughout winter, normally in late December or early January (Shang et al., 2020). Throughout the summer and autumn months, flower buds exhibit notably slow growth, undergoing the intricate stages of floral organ specification, maturation, and differentiation (Bartolini, Piccolo & Remorini, 2020). In preparation for the impending winter, wintersweet, like many long-lived trees, experiences development termination and enters a state of dormancy (Shen et al., 2021). What distinguishes wintersweet from the majority of flowering trees is its unique flowering season, wherein floral buds emerge and flowers bloom during the winter months. This characteristic is visually depicted in Fig. 1, sourced from Shang et al. (2020). This unusual blooming period necessitates the development of robust cold hardiness in wintersweet flowers. Furthermore, wintersweet flowers display a unique feature in having a fully petaloid perianth without differentiation of petals and sepals (Kubitzki, 1993). These distinctive characteristics make wintersweet an intriguing system for studying various aspects of plant biology, including the regulation of flower development, flowering time, fluorescent bud dormancy, and bud break (Shang et al., 2020).

This review aims to investigate the genetic basis of flower color variation in Chimonanthus praecox, focusing on key genes and molecular pathways regulating pigment biosynthesis and to examine the environmental influences on floral traits, elucidating how factors like temperature, light, and soil composition contribute to variations in flower color and fragrance. Moreover, this review assess the practical applications of understanding Chimonanthus praecox genetics and ecology in landscape design, providing insights for horticulturists to create aesthetically pleasing and ecologically sustainable outdoor environments.

Botanical Overview of Chimonanthus praecox

Chimonanthus praecox, commonly identified as wintersweet or Japanese allspice, is a deciduous shrub native to China and belongs to the Chimonanthus genus within the Calycanthaceae family (Paudel & Heo, 2018). In Chinese culture, it is often referred to as the “Plum Blossom”, while in Persian, it is cultivated as “Gorye Yak” in Iran (Liu et al., 2014; Bell, Stoven & Melathopoulos, 2020; Shang et al., 2020). Characterized by an upright trunk, it features glossy green, opposite leaves that are elliptic-ovate to ovate-lanceolate, measuring between 2 to 11 inches in length and 1 to 5 inches in width (Bell, Stoven & Melathopoulos, 2020). The leaves emerge in spring following fragrant winter blooms and undergo a transformation to yellow hues during the fall season. Wintersweet, distinguished by its unique and fragrant flowers, blooms from February to March, providing a vibrant burst of color and fragrance during the winter months (Shang et al., 2020). These strongly scented flowers, delicately hanging on bare stems, typically showcase petals ranging from sulfur-yellow to pale-yellow, often with a purplish-brown center.

The flowers, measuring 1 to 1.5 inches across, contribute to the shrub’s ornamental beauty (Bell, Stoven & Melathopoulos, 2020). Thriving in conditions of full sun to part shade, wintersweet requires moderate watering and is often recommended for hedge use due to its manageable maintenance level and impressive fall foliage (Bell, Stoven & Melathopoulos, 2020). Wintersweet, beyond its ornamental appeal, is acknowledged for its valuable blooms during dormancy.. Cultivars like Chimonanthus praecox ‘Grandiflorus’ and Chimonanthus praecox ‘Luteus’ have received accolades, including the prestigious Royal Horticultural Society’s Garden Achievement Award (Bell, Stoven & Melathopoulos, 2020). Overall, Chimonanthus praecox stands out not only for its aesthetic qualities but also for its adaptability and contributions to garden landscapes (Shang et al., 2020). As of July 2020, the vegetation of China recognizes several distinct species within the Chimonanthus genus, each contributing to the rich diversity of this botanical group. These species include Chimonanthus grammatus M.C. Liu, Chimonanthus zhejiangensis M.C. Liu Chimonanthus nitens Oliv., Chimonanthus praecox (L.) Link, Chimonanthus campanulatus R.H. Chang & C.S. Ding, and Chimonanthus salicifolius S.Y. Hu (Roh-Hwei & Chen-Sen, 1980; Liu, 1984). The acknowledgment of these species by the Flora of China holds substantial importance for botanical research, conservation initiatives, and the broader comprehension of plant biodiversity in the region (Jamal et al., 2021).

Historically, taxonomic studies of the Chimonanthus genus have predominantly depended on morphological characters (Dai et al., 2012). However, relying solely on morphology for describing and delineating this genus presents challenges, as these characters can be influenced by environmental factors and may vary across different physiological phases of plants (Wang et al., 2014). Past morphological studies have suggested varying numbers of Chimonanthus species, ranging from three to six, and even up to nine based on different morphological evidence (Fan et al., 2010; Dai et al., 2012). However, a recent study utilizing nuclear and chloroplast sequences supported the cataloguing of six species in this genus (Zhou, Renner & Wen, 2006). Two Chimonanthus species, Ch. salicifolius and Ch. praecox, have particularly long histories of utilization and cultivation in China (Dai et al., 2012). Ch. praecox iswidely cultivated for its decorative value, especially its sweetly fragrant flowers, Ch. praecox holds additional medicinal significance, with its leaves, roots, flowers, and seeds being utilized for medicinal purposes (Lv et al., 2012). The inclusion of molecular data in taxonomic studies enhances the understanding of the Chimonanthus genus, contributing to more accurate classifications and aiding in the conservation and sustainable utilization of these plant species.

Morphological features

Chimonanthus praecox, a woody shrub, presents a distinctive and versatile profile in the landscape. With an arching, multi-stemmed, and multi-trunked structure, it attains a height of 10 to 13 ft and spans a width of 8 to 15 ft (Liu et al., 2014). The non-showy fruit of this shrub is characterized by an urn-shaped receptacle bearing 5-8 bean-shaped achenes, making it non-ornamental (Kang et al., 2022). Thriving in dappled sunlight or full sun conditions, Chimonanthus praecox prefers well-drained, moist soils of varying textures, including clay, loam, and sand. With a slow growth rate and a coarse texture, it is well-suited for coastal and piedmont regions (Kang et al., 2022). Beyond its ornamental value, this shrub holds ecological significance by attracting wildlife and providing edible fruit, contributing to the diversity and vitality of landscapes (Lin & Chen, 2020). The leaves of Chimonanthus praecox are opposite, simple, lustrous, and dark green, ranging in length from 2.5 to 6 inches. The veins, lighter in color, are easily distinguishable. These ovate-lanceolate leaves feature an entire margin, acuminate apex, and cuneate base, presenting a rough texture. As autumn approaches, the leaves undergo a transition to a yellow-green color, as depicted in Fig. 2 (Bell, Stoven & Melathopoulos, 2020).

Chimonanthus praecox boasts waxy, cupped flowers, measuring 0.7 to 1 inch, occurring in winter to early spring on leafless branches. Adorned and fragrant with purple centers, these flowers emerge on the preceding season’s growth. The inner tepals are purple or brown, while the outer tepals are yellow (Meng et al., 2021). The stem is squarish, covered with orange-brown and shiny gray-brown lenticels, exhibiting a cane-like development habit (Meng et al., 2021). This versatile shrub finds a place in various landscape themes, including children’s gardens, cottage gardens, and recreational play areas (Lin & Chen, 2020). Its fragrant blooms make it an excellent choice for sensory gardens, especially those designed for the visually impaired. Moreover, Chimonanthus praecox attracts pollinators and songbirds, adding ecological value to pollinator and winter gardens (Pichersky & Gershenzon, 2002). Adaptable and engaging, this deciduous shrub seamlessly integrates into diverse landscapes, enriching outdoor spaces with both aesthetic beauty and biodiversity (Lin & Chen, 2020).

Flower Development and Morphology

Chemical composition of flower fragrance

Traditional and modern methods are employed for the analysis and extraction of volatile organic compounds (VOCs) from plants, with each approach offering unique advantages. Traditional methods include steam distillation and solvent extraction, while modern techniques encompass headspace-solid phase micro extraction (HS-SPME), microwave-assisted extraction and enzyme-assisted extraction, (Madani, Mazouni & Nedjhioui, 2021). A well-established modern method for analyzing flower fragrance, particularly in the context of wintersweet flowers, involves the combination of HS-SPME and gas chromatography-mass spectrometry (GC-MS) (Díaz-Maroto et al., 2008; Feng et al., 2022). This analytical approach allows for the precise quantification and identification of volatile compounds present in the flowers.

Wintersweet flowers are renowned for their intense fragrance, primarily attributed to a combination of volatile benzenoids and terpenoids (including sesquiterpenes and monoterpenes), emitted from nectarines dispersed on the adaxial surface of inner petals (Tian et al., 2019). The key floral fragrance compounds of Chimonanthus praecox, including trans-β-ocimene, benzyl acetate, linalool, caryophyllene, and β-myrcene (Zhou, Xiang & Chen, 2007); benzyl acetate, alloocimene, and methyl salicylate (Zhou & Ni, 2010); benzyl acetate, linalool, and methyl salicylate (Yu, 2013); benzyl alcohol, linalool, and methyl salicylate (Li, 2015); and z-muurolene, elemol, z-elemene, L-bornyl acetate, and β-cubebene, (Li et al., 2008), respectively. Understanding these compounds contributes not only to the appreciation of wintersweet’s olfactory charm but also to potential applications in various industries.

The investigation of floral fragrance compounds in Chimonanthus praecox from various regions has provided valuable insights into the diverse aromatic profiles of this species. Meng et al. (2021) identified 31 floral fragrance compounds in Chimonanthus praecox with dissimilar floral colors in Yunnan, China (Table 1). The main compounds included α-ocimene, eugenol, benzyl acetate, benzyl alcohol, and indole, representing a variety of chemical classes such as phenols, alcohols, terpenes, esters, and heterocyclic compounds. Similarly, studies in different regions revealed varying compositions of floral scent compounds. Li et al. (2022) identified a substantial number of compounds in Chimonanthus praecox from Yunnan, whereas 48, 86, 72, 15, 31, 31, 71, 65 and 33 compounds were identified in Chimonanthus praecox from Chongqing (Zhengguo et al., 2008), Hubei (Li, 2015), Jiangxi (Xu et al., 2006), Japan (Azuma, Totota & Asakawa, 2005), Henan (Zheng et al., 1990), Shanghai (Deng, Song & Hu, 2004) Zhejiang (Li et al., 2009), Shandong (Li et al., 2008), and Turkey (Özderin, Tiğli Kaytanlioğlu & Fakir, 2021) respectively. These compounds belonged to categories such as alcohols, acids, esters, terpenes, aldehydes, aromatic compounds, and ketones, with alcohols being the most predominant. In the floral scent of Chimonanthus praecox, compounds like p-xylene, m-xylene, 2-norbornanemethanol, cyclohepta-1,3,5-triene, o-xylene, germacrene D, 3,4-dimethoxycinnamic acid, and ethylbenzene were identified, contributing to the overall aromatic profile (Meng et al., 2021). The analysis of volatile organic compounds (VOCs) in Chimonanthus praecox flowers revealed three prospective biomarker compounds (n-cetane, n-pentadecane, and n-heptadecane) in both excised and living flowers (Deng, Song & Hu, 2004). These findings showcase the chemical diversity of floral fragrances in Chimonanthus praecox, influenced by geographical locations and environmental conditions.

Genetic basis of flower color and fragrance

The Chimonanthus praecox, 2n = 22, is renowned for its aesthetic value, particularly its visual (color) and olfactory (scent) traits in its winter-blooming flowers (Jiang et al., 2023). The plant exhibits a diverse range of varieties classified into three groups based on tepal color variation: Concolor Wintersweet (Chimonanthus praecox var. concolor): This variety is characterized by yellow middle and inner tepals. Patens Wintersweet (Chimonanthus praecox var. grandiflorus): Featuring yellow middle and red inner petals, this variety adds a touch of vibrancy to the tepal color. Rubrum Wintersweet (Chimonanthus praecox var. intermedius): The distinctive trait of this variety is the presence of red middle and inner petals, contributing to a rich and varied color palette (Jiang et al., 2023). These classifications based on tepal color highlight the diversity within Chimonanthus praecox varieties, providing a spectrum of visual appeal. Such variations contribute to the plant’s popularity in ornamental settings, making it a sought-after choice for those seeking both visual and olfactory delights in winter gardens (Shen et al., 2021).

The study conducted by Shang et al. (2020) aimed to sequence the genome of wintersweet (Chimonanthus praecox). The DNA used for genome sequencing was obtained from an accession planted in the campus of Huazhong Agricultural University. The researchers utilized PacBio long reads for sequencing, generating a total of 76.96 gigabases (Gb) of data. This data represented approximately 98.83-fold high-quality sequence coverage of the wintersweet genome, which was estimated to be 778.71 megabases (Mb) in size based on k-mer frequency analysis. Flow cytometry was employed to estimate the haploid genome size of wintersweet, and the result was found to be 805.88 Mb, consistent with the estimation derived from the k-mer method. Subsequently, the generated contigs were subjected to a polishing process using Quiver, resulting in 1,623 contigs with an N50 length of 2.19 Mb. The N50 length is a statistical measure used in genomics to describe the contiguity of a genome assembly, representing the contig length at which half of the total assembly length is contained in contigs of this size or longer. In this case, the N50 length of 2.19 Mb indicates the contiguity achieved in the assembly process, with longer contigs contributing to this measure (Table 2) (Jiang et al., 2023).

Through a comprehensive genomic study, Shen et al. (2021) have elucidated the molecular foundations of tepal color variation among different wintersweet varieties, with a particular focus on Rubrum wintersweet. The study’s comparative analysis revealed that cyanidin glycosides, present in higher concentrations, critically contribute to the formation of yellow tepals. The key regulatory factor in the biosynthesis of anthocyanins in wintersweet, specifically contributing to the yellow tepal color, is identified as CpMYB1. The mutation of CpMYB1 is implicated in the fading of the red color in the inner tepal of Concolor wintersweet, shedding light on the specific genetic factors influencing the observed variations in tepal color across different wintersweet varieties (Shen et al., 2021). Moreover, beyond the aspect of flower color, the diverse floral scents emitted by different wintersweet varieties underscore the intraspecific variation in the chemical composition and biosynthesis of floral bouquets within the wintersweet genus. This multidimensional approach to understanding both visual and olfactory characteristics enhances the overall appreciation and comprehension of the unique traits exhibited by wintersweet varieties (Lu et al., 2020; Qian et al., 2021; Tian et al., 2020).

The unique blooming season of Wintersweet, occurring in winter rather than the more typical spring flowering of many plants, suggests that it may employ distinct molecular mechanisms in governing flower development (Zhang et al., 2011; Liu et al., 2014). This deviation from the typical flowering season of other plants makes Wintersweet an intriguing subject for studying the genetic and molecular regulation of its flowering process. Furthermore, the variation observed in the floral volatile profiles and pigment compositions among different Wintersweet genotypes adds to its appeal as an ideal target for exploring floral traits in ornamental plants (Yang et al., 2018; Tian et al., 2019). The genome-wide identification of basic helix-loop-helix (bHLH) transcription factors (TFs) is highlighted as a promising avenue for comprehending the biological functions associated with these molecular processes in Wintersweet. However, the current knowledge on the bHLH TF family in Wintersweet is limited, with only a few studies focusing on specific members such as CpbHLH1, CpTT8, CpbHLH13, and CpMYC2 (Zhao et al., 2020), CpTT8 (Qian et al., 2021), CpbHLH13, and CpMYC2 (Aslam et al., 2020). Further research in this direction may provide valuable insights into the regulatory networks governing key aspects of Wintersweet’s unique floral traits.

The recent advancements in genetic research, particularly in flavonoid biosynthesis, have been notable. Researchers have made rapid progress in understanding the mechanisms of pigment biosynthesis, and this includes a focus on flavonoid biosynthesis. Transcriptome and proteome analyses have proven to be valuable tools in elucidating the color biosynthesis mechanisms of various plants, and these methods have been successfully applied in studying commercial plants (Wu, Northen & Ding, 2023). The application of RNA-Seq (transcriptome analysis) and proteomics has been instrumental in uncovering the networks that influence flower color. These techniques enable researchers to identify genes potentially involved in wintersweet flower color biosynthesis. By analyzing the transcriptome and proteome, researchers gain insights into the molecular processes and key players responsible for the distinctive colors and scents observed in wintersweet flowers (Yang et al., 2018).

Environmental factors impacting flower traits

Chimonanthus praecox exhibits a flowering period that varies across different climate zones. The specific timing of flowering can be influenced by regional climate conditions (Xu & Du, 2009). In Northern China, the flowering period typically occurs from February to March, with variations depending on specific locations. For instance, in Beijing, wintersweet starts flowering in late February (Li, Chen & Li, 2012). In Anyang Wintersweet Garden, located in Henan Province, the earliest blooming time is in mid-December (Li et al., 2022), In Sichuan Province, wintersweet enters its initial flowering period in early December (Song, Yuan & He, 2012). Kunming, situated on the Yunnan-Guizhou Plateau in Southwest China, experiences high altitudes, low summer temperatures, and high winter temperatures. In Kunming, wintersweet plants tend to bloom earlier than in other northern regions, usually at the end of November (Li, Yang & Chen, 2022). Wintersweet thrives in cold environments and tends to bloom during low-temperature seasons with minimal rainfall. (Li, Yang & Chen, 2022). The plant is believed to possess genes related to floral development and adaptations, particularly those responding to environmental stress factors (Sui et al., 2012).

The differentiation of buds in plants is a crucial and intricate morphological process that signifies the transition from vegetative growth to reproductive growth. This process not only influences the flowering period but also determines the number of flowers produced (Zik & Irish, 2003). The initiation of bud differentiation marks the end of vegetative growth and the onset of reproductive growth, playing a pivotal role in the overall reproductive strategy of the plant. The mechanisms underlying bud differentiation are complex, and they are often closely linked to the plant’s flowering mechanism. Environmental conditions, including temperature, light, moisture, and mineral content, are key factors that could substantially impact the process of flower bud differentiation (Ito et al., 2014; Xing et al., 2019; Shenping et al., 2020). Various signaling pathways and molecular processes are regulated in response to these environmental factors. Temperature, in particular, has been identified as a crucial environmental factor influencing flower bud differentiation in many plants (Khodorova & Boitel-Conti, 2013; Distefano et al., 2018). Understanding the environmental cues and molecular processes involved in bud differentiation is essential for elucidating the flowering mechanisms of plants. It provides valuable insights into how external factors influence the reproductive development of plants and helps in optimizing conditions for desired flowering outcomes in horticulture.

Physiological Processes Influencing Fragrance and Color

Chimonanthus praecox is a winter-blossoming plant species that holds substantial ornamental value (Zhao et al., 2007; Xiang, Zhao & Chen, 2010). Several molecular studies and practical explorations have been conducted to unravel key mechanisms related to stress resistance, fragrance biosynthesis, cold hardiness, and floral development in this unique species (Xiang, Zhao & Chen, 2010; Sui et al., 2012; Zhao et al., 2020). One distinctive feature of wintersweet is its unique flower structure, characterized by three layers of scale-like tepals: outer tepals, middle tepals, and inner tepals (Yang et al., 2018). These tepals are waxy and translucent, contributing to the overall visual appeal of the flower. The flowers are drooping on the wintersweet branch, with red tepals typically positioned in the center of the flower. The red inner tepals, however, are often barely visible due to their arrangement (Yang et al., 2018). The primary determinant of the overall color of the wintersweet flower is the middle tepals, usually in shades of yellow or light yellow. In contrast, the color of the inner tepals varies from yellow to red. Over the centuries, breeders of wintersweet have obtained new cultivars with red middle tepals. This emphasis on achieving red middle tepals highlights the aesthetic preferences and goals of cultivators working with wintersweet, aiming to enhance its visual appeal and diversity (Yang et al., 2018). The combination of ornamental value, winter blossoming, and unique floral characteristics makes wintersweet a subject of interest for both researchers and horticulturists, contributing to ongoing efforts in breeding and cultivating new and improved varieties.

Ecological and Evolutionary Perspectives

Mesangiosperms, encompassing magnoliids, monocots, and eudicots, represent a dominant group, constituting 99.95% of angiosperm species. Among mesangiosperms, magnoliids have been historically regarded as an early lineage and are classified into four orders: Canellales, Laurales, Magnoliales, and Piperales, comprising approximately 9,000 species (Group, 2016). Magnoliids share distinctive morphological features, including branching-veined leaves, pollen with a single pore, and trimerous flowers (Jiang et al., 2023). Recent advancements in genomics, specifically genome sequencing of various magnoliid species such as Liriodendron chinense, Cinnamomum kanehirae, Persea americana, and Piper nigrum, have provided valuable insights into the evolutionary relationships among eudicots, monocots, and magnoliids (Rendón-Anaya et al., 2017; Chaw et al., 2019; Hu et al., 2019; Chen et al., 2019). Analysis of 502 low-copy nuclear (LCN) gene sets from L. chinense, along with 12 other species, placed magnoliids outside the sister lineage formed by eudicots and monocots (Chen et al., 2019). Similar findings were corroborated by analyses of 176 LCN gene sets from P. americana and other 18 flowering plants, as well as 82 LCN gene sets from P. nigrum and 20 other land plants (Rendón-Anaya et al., 2017; Hu et al., 2019). However, a contrasting phylogenomic analysis, utilizing 211 LCN gene sets from C. kanehirae and 12 other seed plants, suggested that magnoliids might be the sister group to eudicots (Hu et al., 2019).

Chimonanthus praecox, belongs to the Calycanthaceae family within the order Laurales, Calycanthaceae is a small and ancient family consisting of ten species distributed among four genera: Calycanthus L in North America, Sinocalycanthus Cheng & S. Y. Chang, and Chimonanthus L. in China, and Idiospermum black in Australia. These genera exhibit variations in flower color, flowering time, and geographical distribution, contributing to the overall diversity within the Calycanthaceae family (Kubitzki, 1993; Ye & Bingtao, 2000; Zhou, Renner & Wen, 2006).

Genetic studies related to ecological and evolutionary perspective on Chimonanthus praecox have been relatively limited (Zhou, Xiang & Chen, 2007). A study employing amplified fragment length polymorphism (AFLP) and inter simple sequence repeat (ISSR) markers investigated seven natural Chimonanthus praecox populations, revealing high genetic diversity and low gene flow among populations, though the population structure was not explored in depth (Zhao et al., 2007). Another study, utilizing sequence-related amplified polymorphism (SRAP) markers on five natural populations, suggested low genetic diversity, high gene flow, and minimal differentiation among populations in central China (Zuo et al., 2009), However, caution is warranted as the limited number of populations may not fully capture the overall genetic relationships across the species’ distribution. In 2007, genetic diversity was assessed in seventy-two wintersweet clones from two Chinese regions using 11 inter simple sequence repeat (ISSR) and 19 random amplified polymorphic DNA (RAPD) markers (Zhou, Zhao & Chen, 2007; Zhao et al., 2007). High genetic differentiation among these clones was observed, although it’s worth noting that all the clones were propagated asexually.

Conclusion and Future Directions

In conclusion, the exploration of Chimonanthus praecox, or wintersweet, has unveiled a fascinating tapestry of genetic, environmental, and physiological factors influencing its distinctive flower color and fragrance. The bell-shaped flowers, ranging from yellow to red, with unique adaptations to winter blooming, make wintersweet a captivating subject for scientific inquiry and landscape applications. The review emphasizes the pivotal role of genetic makeup in determining floral traits. Studies on pigment biosynthesis pathways, hormone regulation, and metabolic activities provide insights into the intricate processes shaping flower color and fragrance. The identification of specific genes governing pigment synthesis, such as quercetin and cyanidin glycosides, sheds light on the molecular basis of tepal color variation. Environmental factors, including light intensity, temperature, and soil composition, considerably influence wintersweet’s flower characteristics. The synchronization of flowering with seasonal climate changes, especially temperature fluctuations, showcases the plant’s adaptive strategies for enduring cold conditions. Physiological processes, including the influence of hormones like ethylene, contribute to the balance of floral characteristics. The review underscores the importance of understanding temporal aspects and developmental stages in unraveling the factors influencing flower traits. The study of floral scent compounds in different varieties across geographical locations further enriches our understanding of wintersweet’s diverse aromatic profiles. Wintersweet’s position as an ideal candidate for exploring floral traits in ornamental plants is underscored, offering opportunities for landscape applications. In essence, this comprehensive review encapsulates the intricate interplay of genes, environmental factors, and physiological processes that contribute to the enchanting flower color and fragrance of Chimonanthus praecox. The findings not only deepen our understanding of this winter-blooming beauty but also pave the way for leveraging its ornamental and economic potential in diverse landscapes.

The insights derived from this review on the genetic and environmental factors influencing the flower color and fragrance of Chimonanthus praecox offer valuable guidance for landscape architects and horticulturists. By understanding the molecular mechanisms and ecological adaptations of this winter-blooming shrub, landscape designers can strategically incorporate diverse Chimonanthus praecox cultivars to enhance visual and olfactory aesthetics globally. The review serves as a foundation for informed plant selection, allowing for the creation of captivating and sustainable landscapes that thrive in various climates, enriching outdoor spaces with the unique beauty and fragrance of wintersweet blooms.

Future research should leverage the ecological importance of Chimonanthus praecox for pollinator conservation and ecosystem services. Integrating cutting-edge technologies, like CRISPR-based gene editing, offers novel avenues for tailoring specific floral traits. Harnessing these attributes for innovative landscape designs and urban green spaces can contribute to biodiversity and enhance environmental aesthetics. Addressing challenges and advancing research in these future directions holds promise for unlocking the full potential of Chimonanthus praecox in various fields.