Plant Natural Sources of the Endocannabinoid (E)-β-Caryophyllene: A Systematic Quantitative Analysis of Published Literature.

(E)-β-caryophyllene (BCP) is a natural sesquiterpene hydrocarbon present in hundreds of plant species. BCP possesses several important pharmacological activities, ranging from pain treatment to neurological and metabolic disorders. These are mainly due to its ability to interact with the cannabinoid receptor 2 (CB2) and the complete lack of interaction with the brain CB1. A systematic analysis of plant species with essential oils containing a BCP percentage > 10% provided almost 300 entries with species belonging to 51 families. The essential oils were found to be extracted from 13 plant parts and samples originated from 56 countries worldwide. Statistical analyses included the evaluation of variability in BCP% and yield% as well as the statistical linkage between families, plant parts and countries of origin by cluster analysis. Identified species were also grouped according to their presence in the Belfrit list. The survey evidences the importance of essential oil yield evaluation in support of the chemical analysis. The results provide a comprehensive picture of the species with the highest BCP and yield percentages.

1. Introduction

The endogenous cannabinoid system (ECS) plays an important role in the immune response to an infection. At present, two cannabinoid (CB) receptors are described: cannabinoid type 1 receptor (CB1) and cannabinoid type 2 receptor (CB2), both G-protein coupled receptors [1]. The CB2 receptor represents the peripheral CB, due to its expression on circulating immune cells. However, studies have also found CB2 expression in the brain, such as cerebellum and microglial cells [2]. The CB2 receptor is involved in the attenuation of inflammatory immune responses. CB2 receptor pathway activation entails the suppression of cytokine release from immune cells and thereby dampening of the inflammatory response (immunosuppression) [3].

(E)-β-caryophyllene (BCP) is a bicyclic sesquiterpene hydrocarbon which is present in the essential oil of several plant species [4]. The Research Institute for Fragrance Materials (RIFM) evaluated BCP safety and the molecule has been approved by the Food and Drug Administration and by the European Food Safety Authority as a flavoring agent, which can be used in cosmetic and food additives [5]. Reports on oral sub-chronic toxicity support the safety of BCP for its proposed use also in medical food products [5]. BCP has been reported to be active against several disorders, with particular reference to cancer, chronic pain and inflammation [2]. Non-clinical BCP toxicity and an absence of adverse effects have been described [6]. Moreover, BCP can act as a selective agonist of CB2 [1], it activates peroxisome proliferator-activated receptor-α (PPAR α) [7] and has been recently involved in the prevention of lipid accumulation and in the improvement of glucose uptake [8]. Therefore, BCP is a plant-derived bioactive molecule able to improve health and prevent lifestyle diseases. Moreover, the specificity of BCP for the CB2 receptor, mainly expressed in peripheral tissues, and its inability to bind CB1, which is predominantly expressed at the level of the central nervous system, implies that its action is devoid of the known psychoactive effects associated with the activation of CB1 [1,2,9,10]. In this context, BCP is an interesting alternative to the use of Cannabis.

Owing to the growing importance of BCP, it was interesting to evaluate the occurrence of this important endocannabinoid in plant species used for the extraction of essential oils. Therefore, the aim of this work was to look for plant natural sources of BCP in order to provide the pharmaceutical, nutraceutical and aroma industries a summary of plant species, parts used for extraction and geographical origin of plants producing BCP. Moreover, additional information was provided with regards to the content and yield of BCP as well as the occurrence of selected species in the Belfrit list [11], which includes botanicals allowed in food supplements and ensures compliance of botanicals in terms of quality and safety.

2. Results and Discussion

The database search (performed in July 2020) for the term caryophyllene provided 5867 entries. The search was then refined by selecting all papers with a chemical composition description. This selection provided 2604 entries, which were individually analyzed in order to select papers providing information on BCP percentage > 10%. Papers were then analyzed and the species binomial name, the plant family, the country of origin of samples and the plant part extracted were reported along with the BCP percentage and yield percentage. The total number of selected species was 295 (Table 1). Table 1 also lists the presence of the species in the Belfrit list [11].

Table 1

Occurrence of (E)-β-caryophyllene (BCP) in different plant species. n.a., data not available, the essential oil (E.O.) yield is expressed as volume/weight percentage.

Family	Genus	Species and Auth	Geogr. Origin of Sample	Belfrit List	Part Used	E.O. Yield%	BCP%	Code	Ref.
Anacardiaceae	Rhus	coriaria L.	Iran	YES	fruits	0.55	34.3	249	[12]
Anacardiaceae	Spondias	pinnata (Linn. F.) Kurz	Egypt	NO	leaves	2.00	49.9	268	[13]
Annonaceae	Annona	muricata L.	Bénin	YES	leaves	0.10	13.6	30	[14]
Annonaceae	Annona	densicoma Mart.	Brazil	NO	leaves	0.10	14.4	31	[15]
Annonaceae	Annona	senegalensis Pers.	Burkina Faso	NO	leaves	0.73	19.1	32	[16]
Annonaceae	Annona	squamosa L.	India	YES	leaves	0.12	22.9	33	[17]
Annonaceae	Artabotrys	hexapetalus (L. f.) Bhandare	Vietnam	NO	flowers	0.94	11.4	38	[18]
Annonaceae	Cananga	odorata (Lam.) Hook.f. and Thomson	Australia	YES	leaves	0.30	52.0	62	[19]
Annonaceae	Cleistopholis	glauca Pierre ex Engler and Diels	Ivory Coast	NO	leaves	0.19	26.2	81	[20]
Annonaceae	Fissistigma	rubiginosum Merr.	Vietnam	NO	leaves	0.30	28.1	125	[21]
Annonaceae	Goniothalamus	multiovulatus Ast	Vietnam	NO	stems	0.21	35.7	135	[22]
Annonaceae	Melodorum	sp. (Dunal) Hook.f. and Thomson	Australia	NO	leaf	0.15	26.7	182	[23]
Annonaceae	Miliusa	horsfieldii (Bennett) Baillon ex Pierre	Australia	NO	leaves	0.1	20.2	188	[24]
Annonaceae	Mitrephora	zippeliana Miq.	Australia	NO	leaves	0.30	18.1	189	[19]
Annonaceae	Polyalthia	oliveri Engl.	Ivory Coast	NO	leaves	0.13	31.4	237	[25]
Annonaceae	Pseuduvaria	hylandii Jessup	Australia	NO	leaves	0.50	24.1	242	[26]
Annonaceae	Uvariodendron	calophyllum R. E. Fries	Cameroon	NO	stem barks	0.52	32.5	284	[27]
Apiaceae	Berula	erecta (Hudson) Coville subsp. erecta	Serbia	NO	aerial parts	0.01	14.9	52	[28]
Apiaceae	Bilacunaria	anatolica A. Duran	Turkey	NO	aerial parts	0.14	10.3	54	[29]
Apiaceae	Centella	asiatica L.	South Africa	YES	aerial parts	0.06	19.1	75	[30]
Apiaceae	Conium	maculatum L.	Iran	NO	aerial parts	0.20	15.3	85	[31]
Apiaceae	Dorema	aucheri Boiss.	Iran	NO	leaves	0.40	35.7	108	[32]
Apiaceae	Eryngium	vesiculosum Labill.	Australia	NO	aerial parts	n.a.	20.3	116	[33]
Apiaceae	Ferula	glauca L.	Iran	NO	leaves	0.07	24.9	123	[34]
Apiaceae	Grammosciadium	pterocarpum Boiss.	Turkey	NO	aerial parts	n.a.	15.3	136	[35]
Apiaceae	Hippomarathrum	microcarpum (M. Bieb.) B. Fedtsch	Iran	NO	aerial parts	0.85	15.75	145	[36]
Apiaceae	Hippomarathrum	boissieri Reuter et Hausskn	Turkey	NO	aerial parts	0.40	25.6	146	[37]
Apiaceae	Laser	trilobum (L.) Borkh.	Iran	NO	aerial parts	1.80	22.4	165	[38]
Apiaceae	Oenanthe	divaricata (R. Br.) Mabb.	Spain	NO	aerial parts	0.20	15.3	206	[39]
Apiaceae	Ostericum	viridiflorum (Turcz.) Kitagawa	China	NO	aerial parts	0.03	24.3	210	[40]
Apiaceae	Pimpinella	kotschyana Boiss.	Iran	NO	seeds	5.16	49.9	224	[41]
Apiaceae	Prangos	uloptera DC.	Iran	NO	aerial parts	0.70	18.2	240	[42]
Apiaceae	Zosima	absinthifolia Link	Iran	NO	aerial parts	0.20	22.2	295	[43]
Apocynaceae	Allamanda	cathartica L.	Brazil	NO	flowers	n.a.	15.7	21	[44]
Apocynaceae	Aspidosperma	cylindrocarpon Muell. Arg.	Brazil	NO	leaves	0.03	14.3	45	[45]
Apocynaceae	Tabernaemontana	catharinensis A. DC.	Brazil	NO	leaves	0.30	56.9	272	[46]
Araliaceae	Schefflera	stellata (Gaertn.) Harms	India	NO	leaves	0.10	19.2	260	[47]
Aristolochiaceae	Aristolochia	elegans Mast.	Argentina	NO	leaves	n.a.	27.8	36	[48]
Aristolochiaceae	Aristolochia	fordiana Hemsl	China	NO	aerial parts	0.19	11.1	37	[49]
Asteraceae	Achillea	asplenifolia Vent.	Serbia	NO	aerial parts	0.10	17.6	4	[50]
Asteraceae	Achyrocline	alata (D.C.)	Brazil	NO	leaf and flowers	4.00	16.0	5	[51]
Asteraceae	Acroptilon	repens (L.)	Iran	NO	aerial parts	0.11	10.0	6	[52]
Asteraceae	Ageratum	fastigiatum (Gardn.) R. M. King et H. Rob	Brazil	NO	branches	0.20	34.9	13	[53]
Asteraceae	Ageratum	conyzoides L.	Portugal	NO	flowers	0.17	24.6	14	[54]
Asteraceae	Anthemis	altissima L.	Iran	NO	flowers	0.03	25.3	34	[55]
Asteraceae	Artemisia	verlotiorum Lamotte	France	YES	aerial parts	0.20	12.7	39	[56]
Asteraceae	Artemisia	parviflora Roxb	India	NO	aerial parts	0.20	15.3	40	[57]
Asteraceae	Artemisia	roxburghiana Besser var. purpurascens (Jacq.) Hook	India	NO	aerial parts	0.85	18.4	41	[58]
Asteraceae	Artemisia	capillaris Thunb	South Korea	YES	aerial parts	n.a.	11.1	42	[59]
Asteraceae	Artemisia.	stricta Edgew. f. stricta Pamp	India	NO	aerial parts	0.46	13.4	43	[60]
Asteraceae	Artemisia.	lavandulaefolia DC	South Korea	NO	aerial parts	n.a.	16.1	44	[61]
Asteraceae	Aspilia	africana (Pers.) C. D. Adams	Nigeria	NO	leaves	0.02	10.8	46	[62]
Asteraceae	Baccharis.	articulata (Lam.) Pers	Argentina	NO	aerial parts	n.a.	16.8	48	[63]
Asteraceae	Bidens	pilosa L.	Cameroon	NO	leaves	n.a.	27.1	53	[64]
Asteraceae	Centaurea	zlatiborensis Zlatkovic, Novakovic and Janackovic	Serbia	NO	flowers	n.a.	28.3	73	[65]
Asteraceae	Centaurea	appendicigera C. Koch	Turkey	NO	aerial parts	0.18	17.5	74	[66]
Asteraceae	Centratherum	punctatum Cass	Nigeria	NO	leaves	n.a.	16.6	76	[67]
Asteraceae	Chromolaena	odorata L.	Togo	NO	aerial parts	0.50	25.2	78	[68]
Asteraceae	Conyza	bonariensis (L.) Cronquist	Brazil	NO	aerial parts	0.20	14.4	87	[69]
Asteraceae	Cyanthillium	cinereum (L.) H. Rob	Ivory Coast	NO	roots	n.a.	17.0	100	[70]
Asteraceae	Dendranthema	indicum (L.) Des Moul.	China	NO	aerial parts	0.08	13.8	106	[71]
Asteraceae	Emilia	sonchifolia (L.) DC.	India	NO	aerial parts	n.a.	22.7	110	[72]
Asteraceae	Epaltes	alata Steetz	Niger	NO	leaves	0.30	24.0	111	[73]
Asteraceae	Eremanthus	erythropappus (DC.) MacLeish	Brazil	NO	leaves	0.12	29.3	113	[74]
Asteraceae	Erigeron	ramosus (Walt.) B.S.P.	Korea	NO	flowers	0.40	24.0	114	[75]
Asteraceae	Eriocephalus	luederitzianus O.Hoffm.	South Africa	NO	aerial parts	0.10	13.3	115	[76]
Asteraceae	Eupatorium	triplinerve Vahl	India	NO	leaves	0.40	14.7	120	[77]
Asteraceae	Flourensia	campestris	Argentina	NO	aerial parts	0.02	15.3	127	[78]
Asteraceae	Helichrysum	indutum Humbert	Madagascar	NO	aerial parts	0.19	33.1	141	[79]
Asteraceae	Helichrysum	kraussii Sch. Bip.	South Africa	NO	aerial parts	n.a.	30.7	142	[80]
Asteraceae	Helichrysum	melaleucum Rchb. ex Holl.	Spain	NO	aerial parts	0.10	35.4	143	[39]
Asteraceae	Koanophyllon	villosum (Sw.) King et Robins	Cuba	NO	aerial parts	0.45	17.0	160	[81]
Asteraceae	Laggera	oloptera (DC.) C. D. Adams	Cameroon	NO	leaves	0.05	20.4	161	[82]
Asteraceae	Microglossa	pyrrhapappa var. pyrrhopappa (A. Rich) Agnew	Kenya	NO	leaves	0.40	20.3	185	[83]
Asteraceae	Mikania	cordata (Burm.f.) B.L. Robinson var. cordata	Ivory Coast	NO	leaves	0.63	11.8	187	[84]
Asteraceae	Oyedaea	verbesinoides DC.	Venezuela	NO	leaves	0.05	27.1	211	[85]
Asteraceae	Perymenium	grande Hemsl. var. nelsonii (Robins. and Greenm.) Fay	Costa Rica	NO	leaves	0.30	30.5	217	[86]
Asteraceae	Petasites	japonicus (Siebold and Zucc.) Maxim.	Japan	NO	leaves	0.02	21.9	218	[87]
Asteraceae	Pluchea	carolinensis (Jacq.) Sweet	Martinique	NO	leaves	0.11	21.1	236	[88]
Asteraceae	Porophyllum	obscurum (Spreng.) D.C.	Argentina	NO	leaves	0.30	14.1	238	[89]
Asteraceae	Solidago	decurrens Lour	China	NO	leaves	0.37	15.4	266	[90]
Asteraceae	Tagetes	patula L.	Austria	NO	flowers	0.15	53.5	273	[91]
Asteraceae	Tagetes	erecta L.	Iran	YES	flowers	0.35	35.2	274	[92]
Asteraceae	Tanacetum	punctatum (Desr.) Grierson	Iran	NO	aerial parts	0.1	21.1	275	[93]
Asteraceae	Tarchonanthus	trilobus var. galpinii (Hutch. and E.Phillips) Paiva	South Africa	NO	leaves	0.14	30.4	276	[94]
Asteraceae	Vernonia	chalybaea Mart.	Brazil	NO	aerial parts	0.10	39.1	287	[95]
Asteraceae	Vernonia	scorpioides (Lam.) Pers.	Brazil	NO	aerial parts	0.10	30.6	288	[96]
Asteraceae	Xanthium	strumarium L.	Pakistan	NO	leaves	n.a.	17.5	291	[97]
Asteraceae,	Leptocarpha	rivularis DC.	Chile	NO	aerial parts	0.15	21.1	168	[98]
Atherospermataceae	Daphnandra	repandula (F.Muell.) F.Muell.	Australia	NO	aerial parts	0.20	12.2	105	[99]
Boraginaceae	Cordia	leucocephala Moric	Brazil	NO	leaves	0.04	39.0	91	[100]
Boraginaceae	Cordia	multispicata Cham.	Brazil	NO	leaves	0.25	56.6	92	[101]
Burseraceae	Bursera	aromatica (Proctor)	Jamaica	NO	leaves	0.03	21.7	59	[102]
Burseraceae	Bursera	microphylla A. Gray	USA	NO	oleo-gum-resin	2.10	72.9	60	[103]
Burseraceae	Canarium	parvum Leen.	Vietnam	NO	leaves	0.20	18.7	63	[104]
Burseraceae	Dacryodes	edulis (G. Don) H. J. Lam	Nigeria	NO	leaves	0.08	26.0	103	[105]
Burseraceae	Protium	heptaphyllum (Aubl.) March.	Brazil	YES	leaves	0.30	18.6	241	[106]
Cannabaceae	Cannabis	sativa L. ssp. spontanea	Austria	YES	aerial parts	n.a.	16.2	64	[107]
Cannabaceae	Cannabis	sativa L.	Italy	YES	flowers	0.10	23.8	65	[108]
Cannabaceae	Humulus	lupulus L.	USA	YES	aerial parts	n.a.	22.0	148	[109]
Caryophyllaceae	Dianthus	caryophyllus L.	Iran	YES	aerial parts	n.a.	34.8	107	[110]
Cephalotaxaceae	Cephalotaxus	harringtonia K.Koch subsp. harringtonia	India	NO	twigs	0.01	21.1	77	[111]
Clusiaceae	Clusia	nemorosa G. Mey	Brazil	NO	fruits	0.30	48.6	83	[112]
Clusiaceae	Garcinia	atroviridis Griff. ex T. Anders.	Malaysia	NO	fruits	n.a.	23.8	128	[113]
Clusiaceae	Kielmeyera	rugosa Choisy	Brazil	NO	fruits	n.a.	16.4	158	[114]
Clusiaceae	Pentadesma	butyracea Sabine	Benin	NO	barks	0.08	74.0	214	[115]
Clusiaceae	Psorospermum	corymbiferum Hochr	Nigeria	NO	leaves	0.02	46.8	245	[116]
Convolvulaceae	Convolvulus	persicus L.	Iran	NO	aerial parts	0.04	47.0	86	[117]
Cupressaceae	Cedrus	atlantica G. Manetti	Algeria	NO	twigs	0.02	11.4	72	[118]
Cupressaceae	Juniperus	macrocarpa Sibth. and Sm. (Jom)	Turkey	NO	fruits	n.a.	29.6	156	[119]
Cupressaceae	Thuja	orientalis L.	Egypt	NO	aerial parts	2.60	24.0	281	[120]
Cyperaceae	Cyperus	glomeratus L.	Serbia	NO	rhizomes and roots	0.06	12.6	102	[121]
Ehretiaceae	Varronia	curassavica Jacq.	Brazil	NO	leaves	0.6	41.2	285	[122]
Ehretiaceae	Varronia	schomburgkii (DC.) Borhidi	French Guiana	NO	aerial parts	0.06	47.0	286	[123]
Euphorbiaceae	Acalypha	fruticosa Forssk	India	NO	leaves	1.40	42.0	2	[124]
Euphorbiaceae	Alchornea	tiliifolia (Benth.) Muell.	Vietnam	NO	aerial parts	n.a.	10.7	20	[125]
Euphorbiaceae	Croton	rhamnifolioides Pax and Hoffm	Brazil	NO	leaf	0.21	33.3	94	[126]
Euphorbiaceae	Croton	glandulosus L.	Brazil	NO	aerial parts	0.12	53.2	95	[127]
Euphorbiaceae	Croton	pulegiodorus Baill.	Brazil	NO	aerial parts	5.00	20.9	96	[128]
Euphorbiaceae	Phyllanthus	muellerianus (O. Kuntze) Exell	Nigeria	NO	leaves	0.12	41.9	223	[129]
Fabaceae	Bauhinia	rufa Steud.	Brazil	NO	leaves	0.01	15.8	50	[130]
Fabaceae	Bowdichia	virgilioides Kunt	Brazil	YES	seeds	2.20	44.1	57	[131]
Fabaceae	Caesalpinia	decapetala (Roth) Alston	Japan	NO	aerial parts	0.07	17.2	61	[132]
Fabaceae	Copaifera	langsdorffii Desf.	Brazil	YES	oleoresins	28.00	72.0	88	[133]
Fabaceae	Copaifera	multijuga Hayne	Brazil	NO	oleoresins	n.a.	57.5	89	[134]
Fabaceae	Copaifera	reticulata Ducke	Brazil	NO	oleoresins	n.a.	68.0	90	[135]
Fabaceae	Dalea	carthagenensis L.	Colombia	NO	leaves	0.15	20.7	104	[136]
Fabaceae	Eperua	duckeana Cowan	Brazil	NO	leaves	n.a.	31.8	112	[137]
Fabaceae	Glycyrrhiza	triphylla Fisch. and C.A.Mey	Iran	NO	aerial parts	0.50	25.4	134	[138]
Fabaceae	Psoralea	bituminosa L	Italy	NO	leaves	0.10	23.2	244	[139]
Fabaceae	Rynchosia	minima DC.	Kenya	NO	aerial parts	0.10	30.4	252	[140]
Flacourtiaceae	Casearia	decandra Jacq.	Brazil	NO	leaves	0.20	13.0	67	[141]
Flacourtiaceae	Casearia	sylvestris Swart.	Brazil	NO	leaves	0.60	27.5	68	[142]
Geraniaceae	Geranium	wallichianum D. Don ex Sweet	India	NO	aerial parts	n.a.	15.9	130	[143]
Gramineae	Elyonurns	muticus (Sprengel) O.Kuntze	Brazil	NO	leaves	0.45	17.9	109	[144]
Gramineae	Melinis	minutiflora P. Beauv	Kenya	NO	aerial parts	0.01	24.2	180	[145]
Hernandiaceae	Hernandia	nymphaeifolia (C.Presl) Kubitzki	Australia	NO	leaves	0.01	43.8	144	[146]
Hypericaceae	Hypericum	brasiliense Choisy	Brazil	NO	aerial parts	0.10	29.5	150	[147]
Hypericaceae	Hypericum	perforatum L.	Iran	YES	aerial parts	n.a.	25.05	151	[148]
Hypericaceae	Vismia	baccifera subsp. dealbata (Kunth) Ewan	Venezuela	NO	leaves	0.07	45.7	289	[149]
Juglandaceae	Juglans	regia L.	India	YES	leaves	0.02	15.5	155	[150]
Lamiaceae	Aegiphila	lhotzkiana Cham.	Brazil	NO	leaves	0.02	27.5	9	[151]
Lamiaceae	Ajuga	parviflora Benth.	India	NO	aerial parts	n.a.	22.4	18	[152]
Lamiaceae	Ajuga	comata Stapf.	Iran	NO	aerial parts	n.a.	30.9	19	[153]
Lamiaceae	Ballota	nigra L.	Algeria	YES	aerial parts	n.a.	24.6	49	[154]
Lamiaceae	Clerodendrum	polycephalum Baker	Nigeria	NO	leaves	0.16	28.9	82	[155]
Lamiaceae	Colquhounia	coccinea Wall.	India	NO	flower	0.20	53.2	84	[156]
Lamiaceae	Cunila	incana Benth.	Brazil	NO	aerial parts	0.72	11.3	98	[157]
Lamiaceae	Cyclotrichium.	strussii Bornm	Iran	NO	aerial parts	0.37	16.9	101	[158]
Lamiaceae	Glechoma	hederacea L.	Lithuania	NO	aerial parts	0.05	14.2	131	[159]
Lamiaceae	Glechon	marifolia Benth.	Brazil	NO	leaves	1.40	32.2	132	[160]
Lamiaceae	Hoslundia	opposita Vahl.	Ivory Coast	NO	leaves	0.04	24.8	147	[161]
Lamiaceae	Hymenocrater	calycinus (Boiss.) Benth.	Iran	NO	aerial parts	0.20	32.8	149	[162]
Lamiaceae	Hyptidendron	canum (Pohl ex Benth.) Harley	Brazil	NO	leaves	0.82	41.6	152	[163]
Lamiaceae	Hyptis	mutabilis (Rich.) Briq.	Argentina	NO	aerial parts	n.a.	59.4	153	[164]
Lamiaceae	Hyptis	suaveolens (L.) Poit.	Bénin	YES	fruits	0.10	43.7	154	[165]
Lamiaceae	Lallenmantia	iberica (M. Bieb.) Fisch and CA Mey	Turkey	NO	aerial parts	n.a.	18.3	162	[166]
Lamiaceae	Leonotis	ocymifolia (Burm.f.) M.Iwarsson	South Africa	NO	leaves	0.06	30.8	166	[167]
Lamiaceae	Leonurus	sibiricus L.	Argentina	NO	aerial parts	n.a.	35.2	167	[164]
Lamiaceae	Leucas	aspera (Willd.) Link	India	NO	aerial parts	0.30	34.2	169	[168]
Lamiaceae	Leucas	indica (L.) R.Br	India	NO	aerial parts	n.a.	51.1	170	[169]
Lamiaceae	Marrubium	bourgaei subsp. caricum P.H.Davis	Tunisia	NO	aerial parts	0.07	23.2	175	[170]
Lamiaceae	Marsypianthes	chamnedrys (Vahl) Kuntze	Brazil	NO	aerial parts	n.a.	15.1	176	[171]
Lamiaceae	Melissa	romana Miller	Italy	NO	aerial parts	0.30	15.8	181	[172]
Lamiaceae	Mentha	longifolia (L.) Hudson	Iran	NO	aerial parts	0.41	23.2	183	[173]
Lamiaceae	Micromeria	myrtifolia Boiss. and Hohen.	Turkey	NO	aerial parts	0.20	40.8	186	[174]
Lamiaceae	Mosla	soochowensis Matsuda	China	NO	aerial parts	0.05	12.8	191	[175]
Lamiaceae	Nepeta	fissa C.A. Mey	Iran	NO	aerial parts	0.25	33.1	200	[176]
Lamiaceae	Nepeta	curviflora Boiss.	Lebanon	NO	aerial parts	0.30	50.2	201	[177]
Lamiaceae	Ocimum	tenuiflorum L.	India	YES	aerial parts	0.33	30.0	203	[178]
Lamiaceae	Origanum	majorana L.	Algeria	YES	aerial parts	1.20	26.0	207	[179]
Lamiaceae	Orthodon	dianfhera Maxim.	Vietnam	NO	aerial parts	0.20	52.9	208	[180]
Lamiaceae	Orthosiphon	pallidus Royle, ex Benth	India	NO	aerial parts	n.a.	17.4	209	[181]
Lamiaceae	Perilla	frutescens var. japonica (Hassk.) H.Hara	China	YES	leaves	0.11	37.2	215	[182]
Lamiaceae	Phlomis	crinita Cav. ssp. mauritanica Munby	Tunisia	NO	aerial parts	0.10	40.8	220	[183]
Lamiaceae	Phlomis	rigida Labill.	Turkey	NO	aerial parts	0.05	38.7	221	[184]
Lamiaceae	Platostoma	menthoides (L.) A. J. Paton	Sri Lanka	NO	aerial parts	0.50	37.0	233	[185]
Lamiaceae	Plectranthus	rugosus Wall.	India	NO	leaves	n.a.	38.4	234	[186]
Lamiaceae	Pycnostachys	eminii Gürke	Ethiopia	NO	leaves	0.13	21.6	246	[187]
Lamiaceae	Rosmarinus	officinalis L	Lebanon	YES	aerial parts	0.09	12.9	251	[188]
Lamiaceae	Salvia	palaefolia Kunth	Colombia	NO	aerial parts	0.06	32.2	253	[189]
Lamiaceae	Salvia	bracteata Banks and Soland	Iran	NO	aerial parts	0.28	41.4	254	[190]
Lamiaceae	Salvia	hydrangea DC. ex Benth.	Iran	NO	aerial parts	0.20	33.4	255	[191]
Lamiaceae	Salvia	nemorosa L.	Iran	NO	aerial parts	0.12	41.6	256	[192]
Lamiaceae	Salvia	virgata Jacq.	Iran	NO	aerial parts	0.48	46.6	257	[193]
Lamiaceae	Salvia	canariensis L.	Spain	NO	aerial parts	4.00	30.2	258	[194]
Lamiaceae	Salvia	montbretii Benth.	Turkey	NO	aerial parts	0.10	32.8	259	[195]
Lamiaceae	Scutellaria	havanensis Jacq.	Cuba	NO	leaves	0.18	75.6	261	[196]
Lamiaceae	Scutellaria	brevibracteata Stapf. subsp. pannosula	Turkey	NO	aerial parts	n.a.	36.4	262	[197]
Lamiaceae	Sideritis	clandestina subsp. peloponnesiaca (Boiss. and Heldr.) Baden	Greece	NO	aerial parts	1.00	16.4	263	[198]
Lamiaceae	Sideritis	phlomoides Boiss. and Bal.	Turkey	NO	aerial parts	0.20	30.7	264	[199]
Lamiaceae	Stachys	viticina Boiss.	Turkey	NO	aerial parts	0.20	62.3	269	[200]
Lamiaceae	Teucrium	arduini L.	Croatia	NO	aerial parts	0.35	35.4	277	[201]
Lamiaceae	Teucrium	flavum L.	Iran	NO	leaves	0.20	30.7	278	[202]
Lamiaceae	Teucrium	siculum (Raf.) Guss.	Italy	NO	aerial parts	0.10	30.9	279	[203]
Lamiaceae	Teucrium	turredanum Losa and Rivas-Goday	Spain	NO	aerial parts	0.60	32.0	280	[204]
Lamiaceae	Viticipremna	queenslandica Munir	Australia	NO	leaves	n.a.	33.6	290	[205]
Lamiaceae	Ziziphora	taurica M.Bieb. subsp. taurica	Turkey	NO	aerial parts	0.80	24.8	294	[206]
Lauraceae	Aiouea	costaricensis (Mez) Kosterm.	Costa Rica	NO	leaf	0.10	12.0	17	[207]
Lauraceae	Alseodaphne	peduncularis Meisn	Malaysia	NO	leaves	n.a.	24.0	27	[208]
Lauraceae	Aniba	riparia (Nees) Mez	Brazil	NO	leaves	0.30	16.9	29	[209]
Lauraceae	Beilschmiedia	penangiana Gamble	Malaysia	NO	aerial parts	0.10	12.6	51	[210]
Lauraceae	Cassytha	pubescens R.Br.	Australia	NO	aerial parts	0.10	30.9	69	[211]
Lauraceae	Cinnamomum	tamala (Ham) Nees and Eberm.	Pakistan	NO	leaves	0.03	25.3	79	[212]
Lauraceae	Litsea	helferi Hook.f.	Vietnam	NO	leaves	0.30	14.2	172	[213]
Lauraceae	Nectandra	lanceolata Ness	Brazil	NO	leaves	0.20	32.5	198	[214]
Lauraceae	Neolitsea	foliosa (Nees) Gamble var. caesia (Meisner) Gamble	India	NO	leaves	0.10	35.3	199	[215]
Lauraceae	Ocotea	duckei Vattimo-Gil	Brazil	NO	leaves	0.70	60.5	204	[216]
Lauraceae	Ocotea	splendens (Meisn.) Baill	Brazil	NO	leaves	0.35	51.0	205	[217]
Lauraceae	Persea	americana Mill.	Nigeria	YES	leaves	0.20	43.9	216	[218]
Lauraceae	Phoebe	porphyria (Griseb.) Mez.	Argentina	NO	aerial parts	0.15	19.3	222	[219]
Magnoliaceae	Magnolia	obovata Thunb.	Japan	NO	leaves	0.05	23.7	173	[220]
Malvaceae	Pachira	glabra Pasq.	Nigeria	NO	leaves	0.71	14.5	212	[221]
Malvaceae	Triumfetta	rhomboidea Jacq.	Burkina-Faso	NO	aerial parts	0.02	24.2	282	[222]
Meliaceae	Aglaia	odorata Lour.	Thailand	NO	stem	0.07	10.2	15	[223]
Meliaceae	Aphanamixis	polystachya (Wall.) R.Parker	Bangladesh	NO	wood	n.a.	19.4	35	[224]
Meliaceae	Cedrela	fissilis Vellozo	Brazil	NO	leaves	0.06	26.3	70	[225]
Meliaceae	Guarea	macrophylla Vahl. ssp. tuberculata Vellozo	Brazil	NO	leaves	0.15	10.0	137	[226]
Moraceae	Ficus	benjamina L.	Nigeria	NO	leaves	n.a.	17.0	124	[227]
Myricaceae	Morella	pensylvanica (Mirbel) Kartesz	Canada	NO	aerial parts	0.15	14.5	190	[228]
Myristicaceae	Gymnacranthera	canarica (King) Warb.	India	NO	leaves	0.01	23.4	138	[229]
Myristicaceae	Knema	kunstleri Warb.	Malaysia	NO	aerial parts	0.12	23.2	159	[230]
Myristicaceae	Myristica	malabarica Lam.	India	NO	leaves	0.05	27.3	197	[229]
Myrtaceae	Blepharocalyx	salicifolius O.Berg	Brazil	NO	leaves	0.90	22.9	55	[231]
Myrtaceae	Eucalyptus	leptophleba F. Muell.	Australia	NO	leaves	0.01	11.4	118	[232]
Myrtaceae	Eugenia	stipitata McVaugh ssp. sororia	Portugal	NO	leaves	0.35	22.7	119	[233]
Myrtaceae	Feijoa	sellowiana Berg.	France	NO	fruits	0.10	12.0	121	[234]
Myrtaceae	Marlierea	silvatica Kiaersk	Brazil	NO	leaves	0.30	25.4	174	[235]
Myrtaceae	Melaleuca	sphaerodendra var. microphylla (Virot) Craven and J.W. Dawson	New Caledonia	NO	leaves	0.10	28.8	178	[236]
Myrtaceae	Myrcia	cuprea (O. Berg) Kiaersk.	Brazil	NO	aerial parts	0.10	39.1	194	[237]
Myrtaceae	Myrcianthes	pseudo-mato (Legr.) Mc. Vaugh	Argentina	NO	leaves	0.30	18.9	195	[238]
Myrtaceae	Myrciaria	tenella (DC.) Berg	Brazil	NO	leaves	0.40	25.1	196	[239]
Myrtaceae	Ochrosperma	lineare (C.T. White) Trudgen	Australia	NO	aerial parts	0.30	11.6	202	[240]
Myrtaceae	Plinia	edulis (Vell.) Sobral	Brazil	NO	leaves	0.10	21.2	235	[241]
Myrtaceae	Psidium	striatulum DC.	Brazil	NO	leaves	0.10	28.6	243	[242]
Myrtaceae	Syzygium	aromaticum L.	Morocco	YES	buds	8.58	27.5	270	[243]
Myrtaceae	Syzygium	grande (Wight) Walp.	Vietnam	NO	stem	0.12	29.3	271	[244]
Myrtaceae	Uromyrtus	australis A. J. Scott	Australia	NO	leaves	0.12	20.7	283	[245]
Papilionaceae	Meristotropis	xanthioides Vassilez	Iran	NO	aerial parts	3.20	11.8	184	[246]
Phyllanthaceae	Actephila	excelsa (Dazl.) Muell.	Vietnam	NO	leaves	0.15	11.2	7	[247]
Pinaceae	Abies	nephrolepis (Khingan fir)	South Korea	NO	needles	0.40	10.8	1	[248]
Pinaceae	Pinus	pinaster Aiton	Morocco	YES	needles	0.38	22.2	225	[249]
Pinaceae	Pinus	armandii Franch.	Scotland	NO	needles	n.a.	36.3	226	[250]
Pinaceae	Pinus	bungeana Zucc.	South Korea	NO	needles	0.31	27.2	227	[251]
Pinaceae	Pinus	halepensis Mill.	Turkey	NO	needles	n.a.	25.9	228	[252]
Piperaceae	Piper	tuberculatum var. tuberculatum (Micq.) CDC	Brazil	NO	leaves	n.a.	26.3	229	[253]
Piperaceae	Piper	guineense Schumach. and Thonn.	Cameroon	NO	seeds	1.1	57.6	230	[254]
Piperaceae	Piper	nigrum L.	India	YES	seeds	n.a.	45.3	231	[255]
Piperaceae	Piper	maingayi Hk. F.	Malaysia	NO	seeds	0.21	39.6	232	[256]
Piperaceae	Pothomorphe	peltata (L.) Miq.	Brazil	NO	leaves	0.20	68.0	239	[257]
Plantaginaceae	Adenosma	indianum (Lour.) Merr.	China	NO	aerial parts	0.29	10.32	8	[258]
Podocarpaceae	Afrocarpus	mannii (Hook.f.) C.N.Page	S. Tomé e Principe	NO	leaves	0.15	13.1	12	[259]
Ptaeroxylaceae	Cedrelopsis	grevei H. Baillon	Madagascar	NO	barks	n.a.	10.6	71	[260]
Rosaceae	Agrimonia	eupatoria L.	Iran	YES	flowers	1.20	42.8	16	[261]
Rosaceae	Rosa	canina L.	Tunisia	YES	flowers	1.40	32.0	250	[262]
Rubiaceae	Cruciata	laevipes Opiz	Italy	YES	aerial parts	0.70	19.0	97	[263]
Rubiaceae	Geophila	repens (L.) I.M. Johnst	China	NO	aerial parts	0.07	23.3	129	[264]
Rutaceae	Aegle	marmelos (L.) Corr.	Nepal	YES	leaves	0.29	29.6	10	[265]
Rutaceae	Amyris	elimifera L.	Cuba	NO	leaves	0.60	37.8	28	[266]
Rutaceae	Atalantia	buxifolia (Poir.) Oliv.	China	NO	leaves	0.36	25.8	47	[267]
Rutaceae	Boenninghausenia	albiflora Reichb.	India	NO	flowers	0.20	13.1	56	[268]
Rutaceae	Citrus	garrawayi F.M.Bailey	Australia	NO	leaves	0.20	17.6	80	[269]
Rutaceae	Feroniella	lucida (Scheff.) Swing	Thailand	NO	leaves	0.12	26.6	122	[270]
Rutaceae	Flindersia	pimenteliana F.Muell.	Australia	NO	leaves	0.03	16.9	126	[271]
Rutaceae	Haplophyllum	villosum (M. B.) G. Don	Iran	NO	aerial parts	0.22	13.1	139	[272]
Rutaceae	Medicosma	obovata T.G. Hartley	Australia	NO	aerial parts	0.40	17.2	177	[273]
Rutaceae	Melicope	peninsularis T.G. Hartley	Australia	NO	leaves	0.10	49.0	179	[274]
Rutaceae	Murraya	paniculata L.	Brazil	NO	leaves	0.03	57.6	192	[275]
Rutaceae	Murraya	koenigii (L.) Spreng	India	YES	leaves	0.1	45.9	193	[276]
Rutaceae	Pamburus	missionis (Wight) Swingle	India	NO	leaves	0.05	25.4	213	[277]
Rutaceae	Spiranthera	odoratissima A. St. Hil.	Brazil	NO	leaves	n.a.	23.8	267	[278]
Rutaceae	Zanthoxylum	veneficum F.M.Bailey	Australia	NO	leaves	0.10	36.3	292	[279]
Sapindaceae	Acer	truncatum Bunge	China	NO	leaves	n.a.	12.9	3	[280]
Schisandraceae	Kadsura	coccinea (Lem.) A.C. Smith	China	NO	roots	0.20	24.9	157	[281]
Scrophulariaceae	Buddleia	asiatica Lour.	India	NO	leaves	0.30	15.8	58	[282]
Scrophulariaceae	Capraria	biflora L.	Brazil	NO	leaves	0.09	29.6	66	[283]
Solanaceae	Solanum	stipulaceum Roem and Schult	Brazil	NO	flowers	0.08	25.8	265	[284]
Verbenaceae	Aloysia	virgata Juss.	Cuba	NO	aerial parts	n.a.	15.4	22	[285]
Verbenaceae	Lantana	montevidensis Briq	Brazil	NO	leaves	0.13	31.5	163	[286]
Verbenaceae	Lantana	camara L.	Madagascar	NO	aerial parts	0.08	43.61	164	[287]
Verbenaceae	Lippia	myriocephala Schltdl. et Cham.	Costa Rica	NO	leaves	0.08	16.1	171	[288]
Verbenaceae	Petitia	domingensis Jacq.	Cuba	NO	flowers	n.a.	35.7	219	[289]
Zingiberaceae	Aframomum	corrorima (Braun) P.C.M. Jansen	Ethiopia	NO	leaves	0.50	60.7	11	[290]
Zingiberaceae	Alpinia	purpurata (Viell.)	Fiji	NO	flowers	0.05	24.2	23	[291]
Zingiberaceae	Alpinia	conchigera Griff.	Malaysia	NO	rhizomes	0.14	10.0	24	[292]
Zingiberaceae	Alpinia	mutica Roxb.	Vietnam	NO	fruit	0.17	22.6	25	[293]
Zingiberaceae	Alpinia	pinnanensis T. L. Wu and Senjen	Vietnam	NO	fruit	0.23	11.4	26	[294]
Zingiberaceae	Costus	afer Ker–Grawl	Nigeria	NO	leaves	n.a.	12.3	93	[295]
Zingiberaceae	Curcuma	longa L.	India	YES	rhizomes	2.20	9.8	99	[296]
Zingiberaceae	Etlingera	elatior (Jack) R. M. Smith	Malaysia	NO	leaves	0.70	10.7	117	[297]
Zingiberaceae	Globba	schomburgkii Hook. f.	India	NO	aerial parts	0.01	31.7	133	[298]
Zingiberaceae	Hedychium	coronarium Koen.	Brazil	YES	leaves	0.68	43.0	140	[299]
Zingiberaceae	Renealmia	breviscapa Poepp. and Endl.	Brazil	NO	rhizomes	0.01	62.3	247	[300]
Zingiberaceae	Renealmia	alpinia (Rottb.) Maas	Brazil	NO	leaves	0.50	22.9	248	[301]
Zingiberaceae	Zingiber	nimmonii Dalzell	India	NO	rhizomes	0.04	42.2	293	[302]

In general, the 295 species belonged to 51 families and were reported from 56 countries worldwide. The essential oil containing BCP was extracted from 13 different plant parts. Out of 295 species, 34 were found to be listed in the Belfrit list, whereas for 51 species no data were available on the yield percentage. In many cases, the researchers used a small amount of plant parts (ranging from a few g to 200–300 g) from which it was impossible to evaluate the oil yield. However, in the majority of the other cases the yield was provided and hence reported (Table 1).

The essential oil yield of 243 species ranged from 0.001 to 8.58%, whereas the BCP percentage of all selected species ranged from 9.8 (the threshold minimum level for species selection) to 75.6% (Table 2), providing an average percentage of 0.42% for yield and 27.4% for BCP. As shown in Table 2, variability was higher for yield percentages than for BCP percentage. The reason for the yield and BCP variability depends on several factors, including plant part, the quantity of plant material distilled and, most of all, the genetic variability and phenotypic plasticity of plants [303,304,305,306].

Table 2

General statistics on BCP and yield percentages of plant species listed in Table 1.

Specification	Essential Oil Yield	Percentage of BCP
Number of cases	243	295
Range
Minimum	0.00	9.8
Maximum	8.58	75.6
Mean	0.42	27.4
S.E.M.	0.06	0.8
S.D.	0.87	13.6
C.V. %	2.09	0.5

S.E.M., standard error of the mean; S.D., standard deviation; C.V., coefficient of variation.

In order to look for plant species with the highest BCP and yield percentages, a scatter plot was obtained, as depicted in Figure 1. The highest yield and BCP percentages were found for Copaifera langsdorffii. High BCP percentages but with decreasing yields were found for Bursera microphylla, Scutellaria havanensis and Pentadesma butyracea. Copaifera species, popularly known as copaiba oil, are widely used in Brazilian popular medicine and the genus is known for its high essential oil yield and BCP content [135,307,308]. The genus Bursera belongs to the plant family Burseraceae and contains several aromatic spices producing oleo-gum resins, such as the traditional incenses, frankincense and myrrh [309]. Pentadesma butyracea (Clusiaceae) is a dense forest species which is found in the center and north of Benin forests whose bark, rough and deeply cracked, exudes a thick resinous juice, of reddish yellow color [115]. The Scutellaria genus (Lamiaceae) consists of plants which are widely distributed throughout the world; S. butyracea is an endemic plant native from Havana and is ethnomedically used for several purposes because of its BCP content [196].

Figure 1

Scatter plot of BCP percentage vs. yield percentage. The yield axis is represented as a power of 0.3 scale in order to evidence species with yields ranging from 0.004 to 3%. Numbers correspond to plant species listed in Table 1. Filled circles outline the species outside the central group of all other species (hollow circles).

High yields with lower BCP percentages were found for Acalypha fruticosa, Achyrocline alata, Agrimonia eupatoria, Bowdichia virgilioides, Bursera microphylla, Croton pulegiodorus, Curcuma longa, Glechon marifolia, Laser trilobum, Meristotropis xanthioides, Origanum majorana, Pimpinella kotschyana, Piper guineense, Rosa canina, Salvia canariensis, Spondias pinnata, Syzygium aromaticum and Thuja orientalis. All other species had a yield ranging from 0.004 to 1% and a BCP content ranging from 9.8 to 55 % (Figure 1).

The plant part that contained the highest content of BCP was then analyzed. In order to evidence the statistical linkage between the plant parts, a cluster analysis was calculated by considering as category the plant part and as variables the number of species, the BCP% and the yield% reported in Table 1 (Figure 2). Euclidean distances were calculated by using the average linkage method. Five clusters were evidenced: the first cluster was made by plant parts reported in more than 100 species and was dominated by leaves and aerial parts, which contained in general a BCP percentage lower than 28%. The other four clusters were made by plant parts reported in less than 16 species. These four clusters were further subdivided according to their BCP content (Figure 2). As expected, the highest BCP percentage was found in oleo-gum resins (cluster 2), followed by roots, barks and branches (cluster 3). Flowers and buds (cluster 4) showed a high yield, whereas twigs and woods (cluster 5) had both low yields and BCP percentages (Figure 2).

Figure 2

Cluster analysis of BCP and yield percentages according to the plant part used for extraction. Euclidean distances are calculated with average linkage method. Five clusters are evident (see text for explanation).

Table 3 summarizes the statistical analysis of BCP and yield percentages reported from different plant parts.

Table 3

Average percentages of BCP and yields from plant parts as reported in plant species listed in Table 1. (±S.E.M.); n.c., not computable; E.O., essential oil.

Plant Part	Number of Species	BCP %	E.O. Yield %
Aerial Parts	115	25.19 (±1.10)	0.42 (±4.85)
Barks	3	39.03 (±18.59)	0.30 (±0.22)
Branches	1	34.90 (±n.c.)	0.20 (± n.c.)
Buds	1	27.50 (± n.c.)	8.58 (± n.c.)
Flowers	16	29.29 (±3.11)	0.41 (±0.13)
Fruits	9	26.93 (±4.43)	0.24 (±0.07)
Leaves	128	27.58 (±1.15)	0.30 (±0.04)
Oleo-gum resin	4	66.13 (±4.54)	15.50 (±8.30)
Rhyzomes	5	27.38 (±10.65)	0.49 (±0.43)
Roots	7	39.77 (±5.37)	1.77 (±0.92)
Stems	3	25.07 (±7.66)	0.13 (±0.04)
Twigs	2	16.25 (±4.85)	0.02 (±0.01)
Wood	1	19.40 (± n.c.)	0.42 (±n.c.)

The next analysis was at the familial level. A cluster analysis was calculated with average linkage method by using data of Table 1 by considering as a category the plant families and the species number, yield% and BCP% as variables. The results of the cluster analysis show the presence of 6 clusters (Figure 3). The first cluster is made by the Asteraceae and the Lamiaceae which consist of a number of species > 50 and a BCP% < 31. The second cluster gathers all families whose species have a BCP% > 35%; in this cluster, the Magnoliaceae and the Papilionaceae are separated in a subcluster because of their high BCP% and low yield%, whereas the Fabaceae (which include the above mentioned C. langsdorffii) are separated in a subcluster because of their high yield %. The third cluster is made by families with a number of species > 13 and a BCP% > 23%; here, the Lauraceae, the Apiaceae and the Zingiberaceae are separated in a subcluster because of their higher BCP%. The genus Ocotea is one of the largest of the Lauraceae family, with approximately 350 species distributed throughout tropical and subtropical America. O. splendens, as many other Ocotea species [212] is characterized by a high percentage of BCP [217]. In the Apiaceae family, the species P. kotschyana spreads widely through Anatoly, Iran (northwest, west and center) and north of Iraq and contains BCP in all plant parts [41]. The family Zingiberaceae is well known for producing essential oils that are used to prevent and control several diseases; the species R. breviscapa was found to possess a high percentage of BCP [300]. The fourth cluster is made by families with a BCP% > 26 and a subcluster separates the Atherospermaceae, the Flacourtiaceae and the Meliaceae because of their BCP%. The fifth cluster is made by families with a BCP% < 25 and the Plantaginaceae are separated in a subcluster because of their relatively higher yield%. Finally, the sixth cluster is made by plant families with a low BCP percentage and a subcluster separates the Hernandiaceae, the Juglandaceae, the Phyllanthace and the Ptaeroxylaceae because of their BCP content lower than 11%.

Figure 3

Cluster analysis of BCP and yield percentages according to the plant families. Euclidean distances are calculated with average linkage method. Six clusters are evident (see text for explanation).

Table 4 describes the statistical data related to plant families.

Table 4

Average percentages of BCP and yields from plant families belonging to the plant species reported in Table 1. (±S.E.M.); n.c., not computable; n.a., not available; E.O., essential oil.

Family	Number of Species	BCP%	E.O. Yield%
Anacardiaceae	2	13.25 (±2.65)	n.a.
Annonaceae	15	22.17 (±1.26)	0.20 (±0.05)
Apiaceae	16	30.96 (±4.15)	0.37 (±0.14)
Apocynaceae	3	17.63 (±3.05)	0.26 (±0.10)
Araliaceae	1	39.00 (n.c.)	0.04 (n.c.)
Aristolochiaceae	2	26.65 (±3.75)	0.21 (±0.13)
Asteraceae	50	27.94 (±1.92)	0.47 (±0.14)
Atherospermaceae	1	32.20 (n.c.)	0.06 (n.c.)
Boraginaceae	2	22.95 (±10.15)	0.15 (±0.10)
Burseraceae	5	24.20 (±4.83)	0.14 (±0.02)
Cannabaceae	3	20.24 (±5.14)	0.27 (±0.14)
Caryophyllaceae	1	46.60 (n.c.)	0.48 (n.c.)
Cephalotaxaceae	1	41.60 (n.c.)	0.82 (n.c.)
Clusiaceae	5	25.85 (±6.84)	0.29 (±0.19)
Convolvulaceae	1	15.10 (n.c.)	n.a.
Cupressaceae	3	23.83 (±9.60)	1.59 (±0.84)
Cyperaceae	1	38.40 (n.c.)	n.a.
Ehretiaceae	2	41.95 (±15.65)	1.10 (n.c.)
Euphorbiaceae	6	25.60 (±15.42)	0.42 (±0.46)
Fabaceae	11	36.92 (±6.15)	3.89 (±3.45)
Flacourtiaceae	2	27.75 (±3.15)	n.a.
Geraniaceae	1	13.10 (n.c.)	0.22 (n.c.)
Gramineae	2	27.90 (±13.50)	0.19 (±0.09)
Hernandiaceae	1	9.80 (n.c.)	2.20 (n.c.)
Hypericaceae	3	41.10 (±15.86)	0.13 (±0.05)
Juglandaceae	1	10.00 (n.c.)	0.15 (n.c.)
Lamiaceae	57	31.03 (±2.03)	0.41 (±0.17)
Lauraceae	13	29.33 (±3.14)	0.38 (±0.18)
Magnoliaceae	1	56.90 (n.c.)	0.30 (n.c.)
Malvaceae	2	19.70 (±5.20)	0.11 (±0.04)
Meliaceae	4	30.55 (±9.27)	0.14 (±0.03)
Moraceae	1	37.80 (n.c.)	0.60 (n.c.)
Myricaceae	1	18.10 (n.c.)	0.30 (n.c.)
Myristicaceae	3	42.93 (±10.61)	1.35 (±0.85)
Myrtaceae	15	23.49 (±2.17)	0.27 (±0.08)
Papilionaceae	1	52.00 (n.c.)	0.30 (n.c.)
Phyllanthace	1	10.70 (n.c.)	n.a.
Pinaceae	5	23.22 (±5.33)	0.20 (±0.06)
Piperaceae	5	19.70 (±2.26)	0.23 (±0.07)
Plantaginaceae	1	20.90 (n.c.)	5.00 (n.c.)
Podocarpaceae	1	12.90 (n.c.)	n.a.
Ptaeroxylaceae	1	11.30 (n.c.)	0.72 (n.c.)
Rosaceae	2	18.00 (±6.60)	0.10 (±0.08)
Rubiaceae	2	17.15 (±0.25)	0.03 (n.c.)
Rutaceae	15	22.97 (±2.69)	0.27 (±0.06)
Sapindaceae	1	36.30 (n.c.)	n.a.
Schisandraceae	1	32.00 (n.c.)	1.40 (n.c.)
Scrophulariaceae	2	21.75 (±0.65)	0.10 (n.c.)
Solanaceae	1	12.20 (n.c.)	0.20 (n.c.)
Verbenaceae	5	24.70 (±6.58)	1.59 (±1.20)
Zingiberaceae	13	28.61 (±4.25)	0.22 (±0.06)

The next analysis aimed to evidence the geographical areas from which the plant species listed in Table 1 were collected. A cluster analysis was calculated with average linkage method, considering the country of origin as a category of their species number, yield% and BCP% as variables. The results of the cluster analysis show the presence of 6 clusters (Figure 4). The first cluster gathers countries with the highest number of species and a BCP percentage higher than 28%; here, a subcluster separates Brazil from India and Iran because of the higher number of species, in agreement with the literature data [310]. The second and third clusters identify countries where BCP has the highest percentages, whereas the fourth cluster gathers countries with a number of species higher than 8. The fifth cluster is made by countries where the BCP content is the lowest, whereas the sixth cluster is made by two subclusters with BCP percentages ranging from 18 to 25%. One of these subclusters is made by countries (Colombia, Fiji, Kenya, Morocco, Niger, North Korea, Portugal and Togo) where the species had a BCP percentage higher than 24% (Figure 4).

Figure 4

Cluster analysis of BCP and yield percentages according to the country of origin of extracts. Euclidean distances are calculated with average linkage method. Six clusters are evident (see text for explanation).

Table 5 summarizes the statistics related to countries of origin.

Table 5

Average percentages of BCP and yields from countries from which plant species reported in Table 1 were sampled. (±S.E.M.); n.c., not computable; n.a., not available; E.O., essential oil.

Country	Number of Species	BCP%	E.O. Yield%
Algeria	3	20.67 (±4.65)	0.61 (±0.59)
Argentina	8	25.85 (±5.41)	0.19 (±0.07)
Australia	18	25.70 (±2.98)	0.18 (±0.04)
Austria	2	34.85 (±18.65)	0.15 (n.c.)
Bangladesh	1	19.40 (n.c.)	n.a.
Benin	3	43.77 (±17.44)	0.09 (±0.01)
Brazil	56	33.01 (±2.20)	1.08 (±0.59)
Burkina Faso	2	21.65 (±2.55)	0.38 (±0.36)
Cameroon	4	34.40 (±8.12)	0.56 (±0.30)
Canada	1	14.50 (n.c.)	0.15 (n.c.)
Chile	1	21.10 (n.c.)	0.15 (n.c.)
China	11	19.26 (±2.54)	0.18 (±0.04)
Colombia	2	26.45 (±5.75)	0.11 (±0.05)
Costa Rica	3	19.53 (±5.61)	0.16 (±0.07)
Croatia	1	35.40 (n.c.)	0.35 (n.c.)
Cuba	5	36.30 (±10.85)	0.41 (±0.12)
Egypt	2	36.95 (±12.95)	2.30 (±0.30)
Ethiopia	2	41.15 (±19.55)	0.32 (±0.19)
Fiji	1	24.20 (n.c.)	0.05 (n.c.)
France	2	12.35 (±0.35)	0.15 (±0.05)
French Guian	1	47.00 (n.c.)	0.06 (n.c.)
Greece	1	16.40 (n.c.)	1.00 (n.c.)
India	29	27.00 (±2.32)	0.34 (±0.11)
Iran	30	28.69 (±2.02)	0.67 (±0.22)
Italy	5	22.54 (±2.55)	0.26 (±0.12)
Ivory Coast	5	22.24 (±3.48)	0.25 (±0.13)
Jamaica	1	21.70 (n.c.)	0.03 (n.c.)
Japan	3	20.93 (±1.94)	0.05 (±0.02)
Kenya	3	24.97 (±2.94)	0.17 (±0.12)
Lebanon	2	31.55 (±18.65)	0.20 (±0.11)
Lithuania	1	14.20 (n.c.)	0.05 (n.c.)
Madagascar	3	29.10 (±9.74)	0.14 (±0.06)
Malaysia	7	20.56 (±3.98)	0.25 (±0.11)
Martinique	1	21.10 (n.c.)	0.11 (n.c.)
Morocco	2	24.85 (±2.65)	4.48 (±4.10)
Nepal	1	29.60 (n.c.)	0.29 (n.c.)
New Caledonia	1	28.80 (n.c.)	0.10 (n.c.)
Niger	1	24.00 (n.c.)	0.30 (n.c.)
Nigeria	10	25.87 (±4.39)	0.19 (±0.09)
North Korea	1	24.00 (n.c.)	0.40 (n.c.)
Pakistan	2	21.40 (±3.90)	0.03 (n.c.)
Portugal	2	23.65 (±0.95)	0.26 (±0.09)
S. Tomé e Prince	1	13.10 (n.c.)	0.15 (n.c.)
Scotland	1	36.30 (n.c.)	n.a.
Serbia	4	18.35 (±3.47)	0.05 (±0.03)
South Africa	5	24.86 (±3.65)	0.09 (±0.02)
South Korea	4	16.30 (±3.83)	0.36 (±0.05)
Spain	4	28.23 (±4.44)	1.23 (±0.93)
Sri Lanka	1	37.00 (n.c.)	0.50 (n.c.)
Thailand	2	18.40 (±8.20)	0.10 (±0.03)
Togo	1	25.20 (n.c.)	0.50 (n.c.)
Tunisia	3	32.00 (±5.08)	0.52 (±0.44)
Turkey	14	29.21 (±3.51)	0.25 (±0.08)
USA	2	47.45 (±25.45)	2.10 (n.c.)
Venezuela	2	36.40 (±9.30)	0.06 (±0.01)
Vietnam	11	22.38 (±4.01)	0.28 (±0.08)

In order to separate which species containing BCP were also represent in the Belfrit list, a scatter plot was obtained by selecting BCP% and yield% as variables (Figure 5). C. langdorffii, S. aromaticum, C. longa and B. virgilioides were characterized by a yield ranging from 2 to 28%, with varying percentages of BCP; on the other hand, high percentages of BCP but lower yields% were found for A. eupatoria, H. coronarium, C. odorata, P. americana and M. keonigi. All other species showed both lower yields and BCP percentage.

Figure 5

Scatter plot of BCP% and yield% of plant species present in the Belfrit list. The yield axis is scaled as a power of 0.2 in order to evidence species with yields ranging from 0.02 to 8.6%. 1, Pinus pinaster Aiton; 2, Ocimum tenuiflorum L.; 3, Aegle marmelos (L.) Corr.; 4, Protium heptaphyllum (Aubl.) March.; 5, Artemisia verlotiorum Lam rinus officinalis L.; 6, Annona squamosa L.; 7, Cannabis sativa L.; 8, Centella asiatica L.; 9, Annona muricata L.; 10, Rosmarinus officinalis L; 11, Perilla frutescens var. japonica (Hassk.) H. Hara.

3. Materials and Methods

3.1. Systematic Analysis of BCP-Containing Plant Species

After a preliminary search by using different databases, the work was performed by using Clarivate Analytics Web of Science as a database (http://apps.webofknowledge.com). The basic search criterion was on the general search for the molecule (caryophyllene), then the exclusion criteria were the presence of BCP and a percentage of BCP in the reported results higher than 10%. Papers reporting the occurrence of BCP where then downloaded and saved as a pdf for further reading and collection of information.

3.2. Statistical Analysis

The binomial name of the species (including the author), the family of belonging, the plant part used, the country of origin of the sample, the yield and the BCP percentages were inserted in a database by using Systat® 10 software (Systat Software Inc., San Jose, California, U.S.A.). Data were organized in columns and used for further processing. Average values along with ranges, standard deviation (S.D.), standard error of the mean (S.E.M.) and coefficient of variation (C.V.) were calculated by considering as grouping categories either the species, families, country of origin or plant part used. As a classification statistical method, a cluster analysis was calculated by considering for each category the total number of species, the BCP percentage and the yield percentage by using Systat® 10 software. Euclidean distances were calculated with the average linkage method. Data were plotted as either scatter plots of yield percentage vs. BCP percentage or dendrograms showing the different clusters according to the calculated distance.

4. Conclusions

The attractiveness of BCP, a natural sesquiterpene present in the essential oil of different plant species, arises from its pharmacological feature as a CB2 receptor agonist. This characteristic, along with the lack of interaction with the CB1, makes BCP an interesting plant endocannabinoid with the advantage of lacking any psychotropic effect, as is typical of some Cannabis extracts [8,311,312].

This systematic analysis of published literature on plant species containing BCP in their essential oils identified the species with the highest yield and BCP content and allowed to select which species are also present in the Belfrit list (i.e., potentially attractive for pharmaceutical and nutraceutical industries).

This survey also evidenced the common practice of many authors to ignore the importance of providing the yield of the distilled essential oil, which represent a basic starting point for all industrial applications of the plant species under study. This problem was often correlated with the low amount of plant material distilled. Although interesting from a chemical-analytical point of view, the sole chemical analysis of the essential oil is not useful if performed on a single plant or a few plants, because it does not provide any information on the population genetic variability, being mainly affected by phenotypic plasticity, which is responsible for individual variations inside a population [305].

This work identified some top species like C. langsdforffii, C. odorata, H. lupulus, P. nigrum and S. aromaticum, which provide a high percentage of BCP along with interesting yields. These species, upon a skillful molecular fractionation to remove undesired/toxic monoterpenes, may provide high percentages of BCP that can be used for the preparation of new drugs or dietary supplements aimed to improve health, prevent lifestyle diseases and act as a valid support for chronical diseases such as pain, metabolic and neurological disorders.