Algeria’s flora occupies a unique biogeographical intersection between the Mediterranean, Saharan and European regions, resulting in remarkable ecological and phytochemical diversity across relatively short spatial gradients (Hemmami et al., 2023). The country harbors a high proportion of endemic and regionally restricted taxa, alongside long-standing ethnobotanical traditions in which aromatic and medicinal plants play central roles in folk therapeutics, food preservation and perfumery (Berreghioua and Ziane, 2025; Belhouala and Benarba, 2021; Miara et al., 2018). This combination of rich species diversity, local endemism and deep ethnopharmacological knowledge makes Algeria a scientifically valuable and socioeconomically significant reservoir of essential oils with considerable potential for natural product research (Guenane et al., 2024; Bouhalla et al., 2023). Indeed, the reported antioxidant activity of Algerian essential oils (EOs) varies considerably, with DPPH IC₅₀ values ranging from as low as 3.64 µg/mL for highly potent species such as Daucus muricatus (Djabou et al., 2014) and 2.55 µg/mL for Artemisia campestris (Bendifallah and Merah, 2023) to over 200 µg/mL for weaker activities observed in some Lamiaceae and Myrtaceae species (Adjaoud et al., 2022; Harkat-Madouri et al., 2015).
       
Essential oils derived from aromatic and medicinal plants are increasingly recognized for their potent antioxidant, antimicrobial and anti-inflammatory properties, making them valuable candidates for pharmaceutical, cosmetic and food applications (Costa et al., 2025; Soussa et al., 2024, Reddy et al., 2018). In recent decades, numerous studies have evaluated the antioxidant potential of EOs obtained from Algerian flora using standard in vitro assays such as DPPH and ABTS, as well as chromatographic profiling (GC-MS) to identify active volatile constituents. These investigations consistently reveal that Algerian EOs exhibit significant radical-scavenging and reducing activities, largely attributed to oxygenated terpenes, phenolic monoterpenes and other bioactive volatiles (Adjaoud et al., 2024; Zellagui et al., 2024). However, substantial heterogeneity exists among reported results, driven by variations in plant species and chemotypes, environmental and climatic conditions, extraction methods and assay protocols.
       
This review synthesizes the antioxidant potential of EOs derived from Algerian flora across diverse bioclimatic zones, from Mediterranean forests to Saharan ecosystems. By critically analyzing peer-reviewed data utilizing standard assays, the study examines correlations between phytochemical composition, plant taxonomy and ecological origins. The analysis aims to identify high-potency chemotypes and taxonomic groups, establishing a structured framework to valorize Algerian aromatic plants as sustainable sources of natural antioxidants and guiding future mechanistic and applied research.
 
Literature search strategy
 
This systematic review was conducted at the Laboratory of Molecular and Cellular Biology, Department of Natural and Life Sciences, 8 May 1945 University of Guelma, Algeria, between January 2024 and June 2025, following the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines (Moher et al., 2010). A comprehensive literature search was performed using major scientific databases, including PubMed, Scopus, Science Direct and Google Scholar, to identify studies investigating the antioxidant activity of essential oils derived from Algerian plants. The search strategy included combinations of the following keywords: “Algerian essential oils”, “antioxidant activity”, “medicinal plants” and “antioxidative properties”. The initial search did not impose temporal restrictions; however, the studies ultimately included in the analysis were published between 2014 and 2025.
 
Study selection criteria
 
All retrieved records were first screened based on their titles and abstracts. The full texts of the remaining papers were then evaluated for eligibility. Only studies that reported both quantitative assessment of antioxidant activity (DPPH, ABTS, or FRAP) and chemical characterization (GC-MS) of the corresponding essential oils were retained. Studies lacking phytochemical data or employing non-extract-based antioxidant evaluations were excluded. To ensure balanced geographical representation, a maximum of three species per climatic region were selected. This threshold was applied to prevent overrepresentation of any single region while capturing the diversity of antioxidant potential across Algeria’s bioclimatic zones. When multiple species from the same region met the inclusion criteria, priority was given to those with the highest reported antioxidant activity. To meet the journal’s word limit, only the top 30 species with the strongest antioxidant activities among the eligible studies were selected for further analysis. The overall study selection process is illustrated in the following PRISMA workflow diagram (Fig 1).


 
Climate classification of plant collection sites
 
The geographical locations of plant samples were identified using available information from the original studies. When necessary, GPS coordinates were used to determine the climatic classification of each location according to the Köppen-Geiger climate classification system  (Beck et al., 2023). The main climatic categories associated with the studied plants included: class 4, hot desert climate; class 5, cold desert climate; class 6, hot steppe climate; class 7, cold steppe climate; class 8, Mediterranean climate with hot summer; and class 9, Mediterranean climate with warm summer.
 
Data analysis
 
The data were systematically organized into a database. When multiple assays were reported, the DPPH assay was prioritized due to its widespread adoption, followed by ABTS and FRAP as supplementary indicators. Descriptive statistics were applied to evaluate the distribution of antioxidant activities across plant families and dominant chemical classes. The data were further visualized using R software (version 4.3.3). A heatmap was generated to illustrate the relative antioxidant potency of essential oils.
 
Overview of selected studies
 
The literature search identified numerous studies investigating the antioxidant activity of essential oils from Algerian medicinal plants. After applying the selection criteria, studies involving approximately 72 plant species were retained for analysis. From this pool, a subset of 30 species was selected for detailed comparative analysis based on data completeness, geographical representation and the range of reported antioxidant activities. This subset encompasses the most potent antioxidant species as well as representative species with moderate and weak activities, providing a comprehensive overview of the antioxidant landscape of Algerian EOs (Table 1).



Phytochemical profile and antioxidant activity
 
The antioxidant activity, measured by DPPH IC₅₀, varied significantly among the 30 species analyzed (Table 1). The most potent activities were observed in species from the Asteraceae and Apiaceae families. A. campestris (IC₅₀= 2.55-2.61 µg/mL) and D. muricatus (IC₅₀= 3.64-5.15 µg/mL) showed the highest radical scavenging capacity, comparable to or exceeding standard antioxidants like vitamin C (IC₅₀= 2.61 µg/mL) (Bendifallah and Merah, 2023; Djabou et al., 2014). These values are superior to those reported for the same species in neighboring regions, such as Morocco (IC₅₀= 355 µg/mL for A. campestris; El Bouny et al., 2021). Notably, C. atlantica (Pinaceae) also demonstrated remarkable activity (IC₅₀ = 6.16 µg/mL), ranking third among the selected species (Belkacem et al., 2021).
       
Species from the Lamiaceae family also demonstrated notable activity, with O. floribundum (IC₅₀ = 18.5±0.2 µg/mL) and T. polium (IC₅₀ = 27.4±0.2 µg/mL) being the most potent (Kerbouche et al., 2015). However, other family members like M. pulegium (IC₅₀= 69.6 µg/mL) showed weaker effects (Abdelli et al., 2016). The weakest activities were observed in M. arvensis (IC₅₀ = 760 ± 200 µg/mL), C. sinensis (IC₅₀ = 752 µg/mL) and M. aquatica (IC₅₀ = 690 µg/mL) (Benabdallah et al., 2018; Ben Miri et al., 2018).
       
Strong activity was consistently associated with high concentrations of phenolic monoterpenes. For instance, D. muricatus and O. floribundum are rich in thymol, while F. vulgare contains eugenol derivatives. In contrast, EOs dominated by non-phenolic compounds, such as ketones (M. pulegium with 70.6% pulegone) or hydrocarbons (T. articulata with α-pinene and camphene), demonstrated lower radical scavenging capacity (Abdelli et al., 2016).
       
This review systematically synthesizes the in vitro antioxidant potential of EOs from Algerian plant species, revealing significant interspecific variability. Ranked by DPPH IC₅₀ values, the most potent activities were recorded in Asteraceae and Apiaceae species, notably D. muricatus (IC₅₀ = 3.64 - 5.15 µg/mL) and A. campestris (IC₅₀ = 2.55- 2.61 µg/mL) (Fig 2). D. muricatus hydrosol extracts outperformed the synthetic standard BHT (IC₅₀ = 12.22 µg/mL), with flowers showing the highest activity (IC₅₀ = 3.64 µg/mL), followed by roots (IC₅₀ = 5.15 µg/mL) (Djabou et al., 2014). A. campestris was comparable to vitamin C, underscoring their exceptional radical-scavenging efficiency. Notably, C. atlantica (Pinaceae) also exhibited very high activity (IC₅₀= 6.16 µg/mL), ranking third and further diversifying the taxonomic range of potent antioxidant species (Belkacem et al., 2021). These values are markedly superior to those reported in neighboring regions, highlighting the unique potency of these Algerian chemotypes. The high activity is attributed to distinct phytochemical profiles; D. muricatus contains phenolic monoterpenes like thymol, while A. campestris is rich in monoterpene hydrocarbons (e.g., β-pinene, limonene) known for synergistic antioxidant effects (Dahiya et al., 2025; Gago et al., 2025; Behtari et al., 2011).


       
Contrary to expectations, the Lamiaceae family did not yield the most potent EOs. To support this observation quantitatively, mean DPPH IC₅₀  values were calculated for the major families represented in this review. The Apiaceae family exhibited the lowest mean IC₅₀ value (50.5±52.1 µg/mL, n = 5), indicating the highest average antioxidant potency, driven largely by the exceptionally low values recorded for D. muricatus (3.64-5.15 µg/mL) and A. pusilla (38.7 µg/mL). The Asteraceae family followed with a mean IC₅₀ of 49.4±64.8 µg/mL (n = 5), reflecting the strong activity of A. campestris (2.55 µg/mL) and S. rebaudiana (7.83 µg/mL). The Pinaceae family, represented by C. atlantica, showed an exceptionally low IC₅₀ of 6.16 µg/mL, indicating that potent antioxidant activity is not restricted to the traditionally studied Apiaceae and Asteraceae. In contrast, the Lamiaceae family showed a mean IC₅₀ of 262.0±53.4 µg/mL (n = 13), with values ranging from 18.5 µg/mL (O. floribundum) to 760 µg/mL (M. arvensis). These averages confirm that, while Lamiaceae contains several potent species, the Apiaceae and Asteraceae families collectively demonstrate superior antioxidant potential among Algerian EOs. Although O. floribundum (IC₅₀ = 18.5 µg/mL) and T. polium (IC₅₀  = 27.4 µg/mL) showed notable activity due to their high thymol content, they were outperformed by Apiaceae and Asteraceae species. The weaker activity of M. pulegium (IC₅₀ = 69.6 µg/mL), despite its high pulegone content, suggests that ketone monoterpenes are less effective antioxidants. Similarly, the very low activity of M. arvensis (IC₅₀ = 760 µg/mL), C. sinensis (IC₅₀ = 752 µg/mL) and M. aquatica (IC₅₀ = 690 µg/mL) reinforces the principle that the presence of phenolic hydroxyl groups is a key molecular determinant of high antioxidant efficacy in EOs.
       
No direct correlation was observed between a single climate class and superior antioxidant activity. Potent species originated from diverse climates, including temperate (D. muricatus) and arid, desert and cold regions (A. campestris). For instance, P. bituminosa (IC₅₀ = 3.1 µg/mL) and S. rebaudiana (IC₅₀ = 7.83 µg/mL) both thrive in Mediterranean climates (class 8), while P. inuloides (IC₅₀  = 14.4 µg/mL) originates from a hot desert climate (class 4). This suggests that antioxidant potential is shaped by fine-tuned, species-specific adaptations to local micro-environmental factors, such as UV exposure, soil salinity and temperature, rather than broad climatic categories (Lonèar et al., 2024; Karalija et al., 2022).
 
Study limitations
 
Despite the growing body of research on Algerian medicinal plants, this review has several limitations. Most available studies are limited to in vitro experiments, while clinical and in vivo investigations remain scarce. In addition, methodological differences in plant collection, extraction procedures and antioxidant assays may affect the comparability of reported results. Future studies should therefore focus on standardized experimental protocols and deeper investigations of phytochemical interactions responsible for antioxidant activity.

This review identifies D. muricatus, A. campestris and C. atlantica as outstanding natural sources of antioxidants from the Apiaceae, Asteraceae and Pinaceae families, with potency comparable to pure ascorbic acid. These findings challenge the prevailing assumption of Lamiaceae dominance in antioxidant activity among EOs and decouple high antioxidant capacity from broad climatic classes. The primary determinant of efficacy is species-specific phytochemical composition, particularly the abundance of phenolic compounds. These data highlight specific Algerian flora as prime candidates for the development of natural antioxidant products.

Not applicable.
 
Funding
 
This work was supported by the General Directorate Scientific Research and Technological Development (DGRSDT), Algeria under grant Number (D00L02UN240 120220002).

The authors of this paper declares no potential conflict of interest.