The chemical composition of the aerial parts essential oil of Ammi crinitum Guss. (Apiaceae) endemic of Sicily (Italy)

Abstract Ammi L. is a small genus of economically important plants belonging to Apiaceae family that includes only six taxa. In the present study the chemical composition of the essential oil from aerial parts of Ammi crinitum Guss., a very rare plant, endemic of Sicily, was analyzed by GC–MS. No previously paper has been published on this species. The results showed the presence of large quantity of monoterpene hydrocarbons with sabinene (63.9%), as the most abundant component. Other metabolites present in good quantity were γ-terpinene (8.0%), and 4-terpineol (3.7%). Based on the composition of the essential oil of all the other Ammi taxa, several considerations have been carried out.


Introduction
Ammi L. is a small genus of summer-flowering plants in the family Apiaceae.They are native to southern Europe, northern Africa, and Southwest Asia and, according to The Plant List (2022), the genus contains six accepted taxa that present fern-like leaves and white or cream coloured lace-like flowers borne in branched, rounded umbels.Among them, by far, the most widely distributed are Ammi majus L. and Ammi visnaga (L.) Lam., typical of the Mediterranean areal (Euri þ Med 2022), while of particular biogeographical interest are A. huntii H. C. Watson and A. trifoliatum (H. C. Watson) Trel., both endemic to the Azorean islands (Euri þ Med 2022), and A. crinitum Guss.endemic species of Sicily (Pignatti et al. 2017(Pignatti et al. -2019)).The last taxon, A. majus subsp.procerum (Lowe) Menezes (syn. A. procerum Lowe), is reported for Gran Canaria but doubtfully native (Euri þ Med 2022; The Plant List 2022).
Despite of the large number of research published on A majus and A. visnaga, the other four taxa of the genus have been completely neglected.
A. crinitum is an annual cycle plant, flowering in spring (April-June), with an erect, branchy, hairless stem with 8-10 longitudinal grooves, 5-16 dm high.The upper branches are bristly and the lower leaves, with very small petioles, have a lamina with a more or less ovate outline, 4-8 cm, inserted directly into the sheath, with linear segments that assume a characteristic curvature in the dry plant material.Umbrellas have about 15 rays, not enlarged and more or less divergent when fruiting; the casing has trisetted external bracts, longer than the rays of the umbrella.The flowers have white petals and fruits show barely detected ribs (Pignatti et al. 2017(Pignatti et al. -2019)).
The two species (A.crinitum and A. visnaga) show partly overlapping characters, but they are easily distinguished on the basis of the bracts of the casing, which in A. visnaga are lanceolate while in A. crinitum are trisetted.Furthermore, the ripe umbels of A. visnaga are contracted, with all the branches enlarged and parallel to each other, while in A. crinitum the branches of the inflorescence remain slender and more or less divergent (Pignatti et al. 2017(Pignatti et al. -2019)).
Consequently, in the frame of our on-going research on accessions of Sicilian plants (Rosselli et al. 2020;Sut et al. 2020;Badalamenti, Rosselli, et al. 2021;Badalamenti, Russi, et al. 2021;Candela et al. 2021), we decided to investigate the composition of the essential oil of A. crinitum, collected in Sicily.

Results and discussion
Hydrodistillation of A. crinitum aerial parts gave a pale-yellow oil (Ac).Overall, eighteen compounds were identified, representing 94.9% of total components, listed in Table S1 according to their retention indices on a DB-Wax column and classified into four classes based on their chemical structures.Monoterpene hydrocarbons formed the main class, representing 81.8% of the oil, with sabinene (63.94%), by far, as the most abundant component.In the same class, c-terpinene (8.0%) was also present in good amounts.Oxygenated monoterpenes were the second most abundant class (4.7%), with 4-terpineol (3.7%) as the main component of this class.Sesquiterpene hydrocarbons occurred in similar amount (4.8%) being germacrene D (1.5%), the principal constituents of the class.
Comparison with the essential oils of other two taxa, belonging to Ammi genus (Tables S2 and S3), studied so far, allowed us to carry out some interesting comments.In fact, the oil from the aerial parts of a German accession of A. majus, although quite rich, as Ac, in monoterpene hydrocarbons (Glass 1975), showed a completely different profile with myrcene (31.4%), limonene (9.0%) and b-phellandrene (8.5%) as main constituents, compounds totally absent in our oil.Another investigation, on the other hands, indicated a huge amount of diterpenoids (Abraham et al. 1996).
Ammi visnaga L. was found to contain essential oils in different organs, but mainly in the umbels and fruits (Table S3).The main chemical constituents of the essential oils of A. visnaga include: nonterpenes, monoterpenes and small amount of diterpenes and sesquiterpenes, with isoamyl 2-methylbutyrate, isoamyl isobutyrate, iso-butyl-2methylbutyrate, 2-methylbutyl 2-methylbutyrate, 2-methylbutyl isobutyrate, and isoamyl isovalerate as main metabolites (Satrani et al. 2004;Zrira et al. 2008;Khadhri et al. 2011;Khalfallah et al. 2011;Sellami et al. 2011;Feirouz and Salima 2014;Keddad et al. 2016;Kamal et al. 2022).Among the monoterpenes, both oxygenated and hydrocarbon, the major component identified was linalool and, in minor quantity, thymol, limonene, and myrcene (Lamiri et al. 2001;Zrira et al. 2008;Khadhri et al. 2011;Khalfallah et al. 2011;Soro et al. 2015;Keddad et al. 2016;Kamal et al. 2022).The results presented in Table S3 clearly show that the nature of the main constituents of the essential oils of A. visnaga depend greatly on the plant organs, its developmental stage, climate, altitude, nature of the soil, etc.By the way, the composition of all the oil of A. visnaga totally differs from the composition of the oil of A. crinitum (Ac).

Conclusions
In our study, the GC analysis of the A. crinitum EO showed that this is rich in monoterpene hydrocarbons with sabinene (63.9%) as the most abundant component.Its composition totally differs from the oils of the other two taxa studied so far, A. majus and A. visnaga, that show the total absence of sabinene.Among all the other oils studied so far, due to its large content in monoterpene hydrocarbons, the most similar is the oil from the aerial parts of a German accession of A. majus (Glass 1975).
Unfortunately, no studies have reported for the other three Ammi taxa and further investigation are hopeful to have a better understanding of this genus.

Disclosure statement
No potential conflict of interest was reported by the authors.