# Lavandula Species, Their Bioactive Phytochemicals, and Their Biosynthetic Regulation
## 1 Introduction  
Lavenders are commonly used as ornamental and melliferous plants [1]. Their essential-oil (EO) content makes them valuable herbs and spices, and of significant importance in industries such as pharmaceuticals, food, flavour, cosmetics, perfumery, and aromatherapy [2]. The pleasant fragrance of lavender is mainly attributed to the content of monotereponoids, concentrated mainly in the flowers and other upper areas of the plant [3]. The lavender oils that are most valued by the perfumery and cosmetics sectors contain higher levels of linaly acetate and linalool, but small levels of camphor. On the other hand, those with a higher camphor content are typically used in aromatherapy and phytotherapy [4]. The economic value of _Lavandula_ spp. is mainly attributed to the properties of its essential oils, which are subject to strict regulation by international ISO (International Organization for Standardization) standards. These oils have been utilized for cosmetic and therapeutic purposes for centuries, with evidence of their therapeutic use dating back to ancient Greek and Roman times. Recently, the rise in popularity of alternative medicines has sparked a renewed interest in _Lavandula_ spp. and their essential oils as natural remedies [5, 6]. Lavender essential oils are primarily composed of monoterepenes, with approximately 50-60 monoterepenes having been identified thus far. However, each species has a unique profile in which a select few molecules play a prominent role in determining the aroma and essential-oil properties [6, 7].  
The prevalent lavender varieties are rich in linalool and linalyl acetate, which are the most frequent monoterepenes they contain [8]. The composition of essential oils is primarily influenced by the genetic makeup of the plant, while environmental and propagation factors can also exert a considerable influence. Furthermore, variations in composition mayexist among different plant tissues [7; 9]. Lavandula species exhibit potential for diverse biological applications, particularly owing to their antioxidant activity. The development of drugs could facilitate the identification and characterization of different bioactive compounds. Investigating the synergistic effects of lavender's bioactive components with other molecules through in vitro and in vivo studies demonstrates an effective option for the treatment conditions related to impaired immune functions and oxidant stresses. The major constituents of lavender, including volatile oils such as linalool, limonene, perillyl alcohol, linalyl acetate, cis-smine, terpene, coumarin, tannin, caffeic acid, and camphor, vary in relative concentrations among different species [10]. The review provides structured insight into the chemical compositions of lavender species and essential oils. The characteristic constituents and chemotypes are presented. The intra- and interspecific variability is considered with respect to geography, occurrence, and morphogenetic determinants, and genetic diversity. We also summarize the status of genomic and transcriptomic sequencing data, including the genetic background and the role of microRNAs in the secondary-metabolites biosynthesis of lavender species.