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. 2023 Feb 5;12(4):703. doi: 10.3390/plants12040703

Volatile Constituents from Catasetum (Orchidaceae) Species with Occurrence in the Brazilian Amazon

Franciléia M de Vasconcelos 1, Eloisa Helena A Andrade 1, Luiz Otávio A Teixeira 2, Pablo Luis B Figueiredo 3, José Guilherme S Maia 1,4,*
Editor: Patrick Meffre
PMCID: PMC9959621  PMID: 36840051

Abstract

Background: Catasetum Rich. ex Kunth is a genus of Neotropical orchids distributed in Central and South American regions. In the Brazilian Amazon, there are more than 60 species of Catasetum. The floral aromas of orchids are little known, particularly of Catasetum species. This work aimed to analyze the chemical constituents of the volatile concentrates of eight Catasetum specimens from the Amazon: C. alatum (1), C. albovirens (2), C. barbatum (1), C. ciliatum (2), C. galeritum (1), and C. gnomus (1). Methods: Gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) analyzed and identified the constituents of the volatile concentrates, and principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used in the multivariate statistical analysis. Results: The Catasetum main constituents in descending order and above 10% were trans-geranylgeraniol, 1,4-dimethoxybenzene, linalool, 2-phenylethyl acetate, geraniol, 7-epi-1,2-dehydro-sesquicineole, 1,8-cineole, benzyl acetate, limonene, methyl salicylate, (E)-β-farnesene, anisyl butyrate, cis-carvone oxide, cadin-4-en-10-ol, indole, α-pinene, and δ-cadinene. Conclusions: Multivariate statistical analysis of Catasetum species showed that C. barbatum, C. albovirens, and C. gnomus are distinct from the other studied species, while C. alatum, C. ciliatum, and C. galeritum presented the same primary classes of compounds. These results contribute to a better understanding of the genus Catasetum chemotaxonomy.

Keywords: floral scents; olfactory signals; principal component and hierarchical cluster analyses; trans-geranylgeraniol; 1,4-dimethoxybenzene; linalool; 2-phenylethyl acetate; geraniol; 7-epi-1,2-dehydro-sesquicineole; benzyl acetate

1. Introduction

Flowering plants and their volatile compounds attract birds, insects, and other animals, including mammals, as pollinators for their reproduction. More than 1700 flower scent compounds, covering 990 taxa, have already been identified [1,2,3]. The flower perianth is primarily responsible for the scent emission, though all floral organs might contribute to the emission of scents. Floral scents are stored in the oily glands, such as the trichomes before it is released into the air as volatile compounds, and in addition to flowers, volatile compounds emitted by other plant organs have involved in its defense mechanisms. Therefore, floral volatiles play a significant role in the plant’s reproductive process by attracting pollinators and acting as repellents and physiological protectors against abiotic stress [2,4]. Floral volatiles are expected to be used in the composition of perfumes, cosmetics, flavors, and therapeutic applications. However, the volatiles emitted by flowers are also the main signals captured by insects to select gratifying flower species associated with the respective flower colors [3,5]. Floral scents are composed of volatile compounds, usually lipophilic and low molecular weight. Based on their origin, function, and biosynthesis, floral scents are grouped into three main classes of compounds: Terpenoids, phenylpropanoids/benzenoids, and fatty acid and derivatives [3,6].

Orchidaceae is the most prominent flowering plant family, with 736 genera and ca 28,000 species, which shows a wide diversity of epiphytic and terrestrial specimens, colonizing almost every earth’s habitat and renowned for their abundance of morphological types, with an unending number of beautiful variations and very well represented in the monocotyledons’ floral evolution [7,8]. The orchids distributed in the natural environment have small sizes and have a limited production of flowers. These restrictions are circumvented by producing visual and olfactory signals to attract pollinators. Developing highly specialized pollination mechanisms to attract effective pollinators is a common strategy in orchids. Specializing these mechanisms leads to the formation of syndromes, in which the set of floral characteristics, including fragrances, is associated with attracting a particular group of pollinators. Euglossini syndrome is widely known among orchids and is characterized by the absence of food resources, with only the production of specialized floral fragrances collected by male Euglossini bees. Floral fragrances not only act as signaling but also represent a reward for bees because some components of these mixtures will compose their pheromones, which is the essential prerequisite for sexual recognition and selection during mating [9,10,11,12].

Catasetum Rich. ex Kunth is one of the genera of Neotropical orchids pollinated by male Euglossini bees. The genus has about 130 species distributed mainly in Central and South American tropical regions. Floral fragrances play a vital role in the diversification of Catasetum. Hybridizations that result in changes in the composition of fragrances also generate differences in pollinators, restricting gene flow and contributing to the origin of new strains. Inflorescences of Catasetum are usually unisexual with distinct morphology and sexual determination according to each individual’s environmental and nutritional characteristics. Catasetum usually shows male or female flowers, but in some situations, may form nonfunctional hermaphroditic flowers and/or flowers of both sexes. Sex expression is controlled by plant size and light intensity. Large plants under strong sunlight usually develop female flowers, whereas younger and smaller plants under moderate light develop male flowers. They are sympatric species that use floral fragrances as a fundamental part of the reproductive isolation mechanism. The composition of these aromas is represented by a mixture of constituents with attractive and repellent action of different proportions, detected in small amounts by male Euglossini bees. Therefore, orchids attract particular species of bees that, in synergy with other floral filters (e.g., morphological characteristics), act as their effective pollinators. [13,14,15,16].

The present work aimed to extract the volatile concentrates and identify the chemical constituents of the flowers of eight specimens from six species of Catasetum: C. alatum (1), C. albovirens (2), C. barbatum (1), C. ciliatum (2), C. galeritum (1), and C. gnomus (1), with occurrence in the Brazilian Amazon. In addition, submit the chemical composition data of these specimens to multivariate analysis, targeting their association with other species/specimens of Catasetum taxonomically close or previously analyzed.

2. Results and Discussion

2.1. Catasetum Rich. ex Kunth

2.1.1. Catasetum alatum M.F.F.Silva & A.T.Oliveira

Botanical description: Epiphyte. Pseudobulbs aggregated, multi-ringed, fusiform, erect; apex abruptly acuminate. Leaves membranous, lanceolate, slightly wavy margins, five to eight leaves per pseudobulb, and three thin veins. Inflorescence 10 to 20 flowers (Figure 1), basal and pendant. Flowers staminate, resupinate jade green, erect, and distribute in the rachis’s middle third. Dorsal sepal lanceolate, erect, slightly concave; lateral sepals erect, linear-lanceolate, green, arched backward, acuminate. Petals oblong-lanceolate, greenish, convex, erect, margins slightly serrated. Fleshy lip, jade-green, 90° angle with the spine; frontal opening or elliptical ostium, internally light green, white spot at base, sack form at middle portion; edges of lateral lobes strongly winged, semi-curled, slightly serrated, asymmetrical, raised; triangular terminal lobe, apiculate, facing downwards, edges smooth [17]. Flowering in December and January.

Figure 1.

Figure 1

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Catasetum alatum. (Source Luiz Otavio Adão).

Geographic distribution: Endemic in Brazil. Occurrence for the North region of Brazil, State of Rondônia, in riparian or gallery forest areas [17].

The specimen of C. alatum in this study was sampled initially in the locality of Vila Nova California, Rondônia, Brazil. Table 1 lists the constituents of its volatile concentrate.

Table 1.

Constituents identified in the volatile concentrate of C. alatum flowers.

Constituents RICal RILit %
α-Pinene 929 932 a 11.8
Sabinene 968 969 a 0.1
β-Pinene 975 974 a 0.5
Myrcene 987 988 a 1.3
α-Phellandrene 1002 1002 a 3.6
δ-3-Carene 1008 1008 a 0.3
Limonene 1024 1024 a 18.2
(E)-β-Ocimene 1043 1044 a 0.2
Bergamal 1049 1051 a 0.1
γ-Terpinene 1054 1054 a 0.2
cis-Linalool oxide 1067 1067 a 0.7
trans-Linalool oxide 1084 1084 a 0.4
p-Cymenene 1089 1089 a 0.2
Linalool 1095 1095 a 8.8
1,3,8-p-Menthatriene 1108 1108 a 0.2
cis-p-Menth-2-en-1-ol 1116 1118 b 0.9
trans-p-Mentha-2,8-dien-1-ol 1118 1119 a 0.8
allo-Ocimene 1128 1128 a 0.3
trans-p-Menth-2-en-1-ol 1135 1136 b 0.6
trans-Limonene oxide 1136 1137 a 3.8
p-Menta-1,5-dien-8-ol 1164 1166 a 0.2
3,7-dimethyl-(Z)-2,6-Octadienal 1173 1174 b 0.3
Terpinen-4-ol 1178 1180 b 0.5
p-Cymen-8-ol 1186 1189 b 1.0
dihydro-Carveol 1190 1192 a 0.1
α-Terpineol 1192 1195 b 0.8
cis-Piperitol 1194 1195 a 0.6
trans-dihydro-Carvone 1204 1200 a 0.2
trans-Piperitol 1208 1207 a 0.7
Coahuilensol methyl ether 1215 1219 a 0.1
trans-Carveol 1218 1223 b 0.7
trans-chrysanthenyl acetate 1227 1231 b 3.9
cis-Carveol 1231 1232 b 0.5
Neral 1233 1235 a 0.1
Carvone 1237 1239 a 0.1
Geraniol 1246 1249 a 29.7
(2E)-Decenal 1258 1260 a 0.4
Geranial 1262 1264 a 0.3
Citronellyl formate 1269 1271 a 0.1
Neryl formate 1279 1280 a 0.1
(4E,4Z)-Decadienal 1294 1292 a 0.1
Perilla alcohol 1298 1294 a 0.1
p-vinyl-Guaiacol 1308 1309 a 0.3
(2E,4E)-Decadienal 1312 1315 a 0.1
Methyl geranate 1321 1322 a 0.7
(2E)-Undecenal 1356 1357 a 0.1
α-Copaene 1374 1374 a 0.1
Geranyl acetate 1378 1379 a 0.2
β-Elemene 1388 1389 a 0.5
β-Longipinene 1400 1400 a 0.1
dihydro-α-Ionona 1411 1411 a 0.1
(E)-Caryophyllene 1415 1417 a 0.4
trans-α-Bergamotene 1427 1432 a 0.1
α-Humulene 1450 1452 a 0.2
Germacrene D 1479 1480 b 0.1
Bicyclogermacrene 1493 1497 b 0.1
α-Muurolene 1496 1500 a 0.1
trans-β-Guaiene 1502 1502 a 0.1
δ-Amorphene 1510 1511 a 0.4
(E)-Nerolidol 1560 1561 a 0.5
Germacrene D-4-ol 1574 1574 a 0.1
Hexadecane 1600 1600 a 0.1
epi-α-Cadinol 1636 1638 a 0.1
epi-α-Muurolol 1638 1640 a 0.1
α-Cadinol 1651 1652 a 0.3
Monoterpene hydrocarbons 36.9
Oxygenated monoterpenes 57.0
Sesquiterpene hydrocarbons 2.2
Oxygenated sesquiterpenes 1.2
Benzenoids/Phenylpropanoids 0.3
Fatty acid and derivatives 0.9
Total (%) 98.5
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RICal = Calculated Retention Index; RILit = Literature Retention Index; a Adams, 2007; b Mondello, 2011; Bold = Main constituents. Unidentified minor constituents were 1.5%.

Oxygenated monoterpenes (57.0%) predominated in the volatile concentrate of C. alatum, followed by monoterpene hydrocarbons (36.9%). The main constituents were geraniol (29.7%), limonene (18.2%), α-pinene (11.8%), and linalool (8.8%) (see Figure 2). The floral scents of C. alatum are being described for the first time.

Figure 2.

Figure 2

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Ion-chromatogram of the Catasetum alatum volatile concentrate.

2.1.2. Catasetum Albovirens Barb. Rodr.

Botanical description: Epiphyte. Fusiform pseudobulbs. Leaves with longitudinal veins, elliptical-lanceolate, sharp at the base, attenuated in canaliculate pseudo petiole. Inflorescence about 25.0 cm, erect and at middle curved in a basal arch, multiflora. Flowers (Figure 3) not resupinate, white-green to pink-green, drooping. Pedicel patent and twisted. Oval or oval-oblong sepals, obtuse or very sharp; erect dorsal sepal with five prominent veins; oblique lateral sepals. Petals lanceolate and acuminate with three very distinct veins. Lip nearly globular, distinctly 3-lobed, crass-fleshy, generally greener than other segments; lateral lobes rounded, entire, curved; terminal lobe patent, reflex, more or less 3-lobed or truncated, glabrous and smooth on the inside. Oval column, with rostellum, acuminate and straight. Antennae about 6.0 mm, extending to the front [17]. Flowering in February to May.

Figure 3.

Figure 3

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Catasetum albovirens. (Source Luiz Otavio Adão).

Synonimy:Catasetum lamosii Rolfe [17].

Geographic distribution: Endemic in Brazil, occurring in the states of Amazonas, Pará, Maranhão, Mato Grosso, and Tocantins, in anthropic areas such as rupestrian fields, high and flooded forests, seasonal deciduous forests, and savannas [17].

Two specimens of C. albovirens were analyzed. Specimen Calb-1 was sampled initially in the municipality of Muaná, Ilha do Marajó, and specimen Calb-2 was collected initially in the municipality of Tucuruí, Pará state, Brazil. Table 2 lists the constituents of their volatile concentrates.

Table 2.

Constituents identified in the volatile concentrates of two specimens of C. albovirens flowers.

Constituents (%) RICal RILit Calb-1 Calb-2
α-Pinene 929 932 a 4.7 0.2
Sabinene 968 969 a 0.5 -
β-Pinene 972 974 a 0.8 -
Myrcene 986 988 a 1.6 3.4
δ-3-Carene 1006 1008 a - -
α-Terpinene 1011 1014 a 0.1 -
Limonene 1023 1024 a - 0.2
1,8-cineole 1025 1026 a 11.7 1.1
(Z)-β-Ocimene 1029 1032 - 0.2
(E)-β-Ocimene 1043 1044 a 0.6 3.8
Bergamal 1049 1051 a 0.8 1.4
γ-Terpinene 1053 1054 a 0.3 -
Terpinolene 1085 1086 a 0.1 -
Linalool 1093 1095 a 10.0 39.5
cis-Rose oxide 1103 1106 a 0.2 0.3
n-Nonanal 1104 1107 a 0.4 0.8
(E)-4,8-dimethyl-Nona-1,3,7-triene 1112 1113 b - 0.1
trans-Rose oxide 1120 1122 a 0.1 -
trans-Limonene oxide 1135 1137 a - 0.1
Nerol oxide 1150 1152 b - 0.2
1,4-Dimethoxybenzene 1160 1161 a 0.4 0.1
δ-Terpineol 1162 1162 a 0.3 -
Terpinen-4-ol 1178 1180 b 0.6
α-Terpineol 1184 1186 a 4.8 1.1
Methyl salicylate 1190 1190 a 0.2 -
trans-Carveol 1212 1215 a 1.0 0.5
Neral 1233 1235 a 0.1 -
Carvone 1237 1239 a - 0.2
Geraniol 1247 1249 a 1.6 1.7
cis-Carvone oxide 1257 1259 a - 0.5
Geranial 1261 1264 a 0.1 0.1
Indole 1289 1290 0.3 -
p-vinyl-Guaiacol 1308 1309 a 0.3 0.2
Methyl anthranilate 1321 1334 a 0.2 -
2,4-Octanediol 1334 1339 a 0.1 -
Citronellyl acetate 1348 1350 a 0.2 0.2
Neryl acetate 1356 1359 a 0.1 -
Geranyl acetate 1378 1379 a 4.2 3.9
9-Decenyl acetate 1398 1399 a 1.0 0.2
Citronellyl propanoate 1442 1444 a - 1.4
(2E)-Dodecen-1-ol 1465 1469 a 3.3 1.6
7-epi-1,2-dehydro-Sesquicineole 1471 1471 a 28.3 19.3
Neryl isobutanoate 1488 1490 a 0.2 -
(E,E)-α-Farnesene 1504 1505 a 1.0 5.2
Myrac aldehyde 1514 1519 a 0.5 -
Hedycaryol 1542 1546 0.5 -
Elemol 1546 1548 a 0.2 -
(E)-Nerolidol 1560 1561 a 0.9 1,5
Anisyl butyrate 1566 1569 c 15.4 7.5
Monoterpene hydrocarbons 8.7 7.9
Oxygenated monoterpenes 36.7 52.4
Sesquiterpene hydrocarbons 1.0 5.2
Oxygenated sesquiterpenes 30.4 20.8
Benzenoids/Phenylpropanoids 16.1 7.6
Fatty acid and derivatives 4.8 2.6
Total (%) 97.7 96.5
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RICal = Calculated Retention Index; RILit = Literature Retention Index; a Adams, 2007; b Mondello,2011; c Nist, 2011. Bold = Main constituents. Unidentified minor constituents were 2.3% and 3.5%, respectively.

The two analyzed specimens of C. albovirens were rich in oxygenated monoterpenes (52.4% and 36.7%), oxygenated sesquiterpenes (30.4% and 20.8%), and benzenoids (7.5% to 15.4%). There was a predominance of linalool (10.0% to 39.5%), 7-epi-1,2-dehydro-sesquicineole (19.3% to 28.3%), anisyl butyrate (7.5% to 15.4%), 1,8-cineol (1.1% to 11.7%), and (E,E)-α-farnesene (1.0% to 5.2%), analyzing both specimens (see Figure 4).

Figure 4.

Figure 4

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Ion-chromatogram of the Catasetum albovirens volatile concentrates.

A previous comparative biology study of C. albovirens showed β-myrcene, eucalyptol (1,8-cineole), (E)-β-ocimene, linalool, 2,4-dimethylacetophenone, indole, (E)-8-hydroxy-linalool, methyl anthranilate, geranyl acetate, and (E,E)-farnesene, as primary constituents [18]. Therefore, presenting some chemical similarities to the two samples currently analyzed.

2.1.3. Catasetum barbatum Lindl.

Botanical description: Epiphytic, occasionally terrestrial. Fusiform pseudobulbs, about 15.0 to 5.0 × 3.0 to 5.0 cm long. Narrow, plicate leaves with a midrib and two lateral ones. Inflorescence suberect or arched with up to 20 flowers. Flowers (Figure 5) male resupinate, greenish with brown spots. Sepals are lanceolate to dorsal erect, the lateral ones reflexed on the pedicel. Petals lanceolate and erect, margins finely serrated, somewhat revolute. The lips include hairs that may be white or greenish; the basal callus may be simple or bifurcated, usually surrounded by pilosity. Column light green or brownish. Cream anther. Yellow pollinia are hard and compressed on a white laminar stipe and a white viscid disc. Flowering in April and May [17].

Figure 5.

Figure 5

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Catasetum barbatum. (Source Luiz Otavio Adão).

Synonimy:Catasetum barbatum var. spinosum Rolfe, C. brachybulbon Schltr., C. buchtienii Kraenzl., C. comosum Cogn., C. crinitum Linden, C. polydactylon Schltr., C. proboscideum Lindl., C. rionegrense Campacci & G.F. Carr, C. spinosum (Hook.) Lindl., C. variabile Barb. Rodr., Myanthus barbatus Lindl., M. barbatus var. immaculatus Knowles and Westc., M. spinosus Hook. [17].

Geographic distribution: Not endemic in Brazil, but found in upland and floodplain forests, broadleaf forests, mangrove and palm groves, and vegetation on rocky outcrops in the states of Amazonas, Pará, Roraima, Tocantins, Alagoas, Bahia, Ceará, Maranhão, Paraíba, Pernambuco, Piauí, Distrito Federal, Goiás, Mato Grosso do Sul, Mato Grosso, and Minas Gerais [17].

The specimen of C. barbatum in this study was sampled initially in the municipality of Ourilândia do Norte, Pará, Brazil. Table 3 lists the constituents of its volatile concentrate.

Table 3.

Constituents identified in the volatile concentrate of C. barbatum flowers.

Constituents RICal RILit %
Hexanal 795 801 a 0.6
2-pentyl-Furan 989 991 a 0.2
1-p-Menthene 1021 1021 a 0.5
Benzene acetaldehyde 1035 1036 a 0.3
(2E)-Octen-1-al 1048 1049 a 0.1
Linalool 1092 1095 a 0.1
n-Nonanal 1097 1100 a 0.5
Naphthalene 1176 1178 b 0.1
cis-carvone oxide 1256 1259 a 0.1
Indole 1289 1290 a 11.3
(E)-β-Farnesene 1451 1454 b 16.4
(E)-Nerolidol 1558 1561 a 0.2
(5E,9E)-Farnesyl acetone 1911 1913 a 1.9
(Z,Z)-Geranyl linalool 1957 1960 b 0.5
(E,E)-Geranyl linalool 2023 2026 b 0.3
n-Heneicosane 2100 2100 b 0.1
trans-Geranylgeraniol 2198 2201 c 61.2
n-Tricosane 2297 2300 b 0.4
2-methyl-tricosane 2365 2365 a 2.2
1-Docosanol 2500 2500 c 0.3
Monoterpene hydrocarbons 0.5
Oxygenated monoterpenes 0.2
Sesquiterpene hydrocarbons 16.4
Oxygenated sesquiterpenes 2.1
Oxygenated diterpenes 62.0
Benzenoids/Phenylpropanoids 11.8
Fatty acid and derivatives 4.3
Total 97.3
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RICal = Calculated Retention Index; RILit = Literature Retention Index; a Adams, 2007; b Mondello, 2011; c Nist, 2011. Bold = Main constituents. Unidentified minor constituents were 2.7%.

In this volatile concentrate of C. barbatum flowers, the major constituents were the trans-geranylgeraniol (61.2%), an oxygenated diterpene, the (E)-β-farnesene (16.4%), a sesquiterpene hydrocarbon, and the indole (11.3%), a heterocyclic aromatic compound (see Figure 6).

Figure 6.

Figure 6

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Ion-chromatogram of the Catasetum barbatum volatile concentrate.

The floral scents of C. barbatum were previously analyzed. Two morphological variants originated from Brazil and Ecuador has differed in fragrance. The Brazilian form showed as primary constituents 1,8-cineole (16.1%), a-pinene (7.9%), and an unidentified main oxygenated monoterpene (46.1%), while the Ecuadorian form displayed ocimene (67.7%) as the main compound [19]. Also, another paper on C. barbatum floral scent presented germacrane-type compounds as the primary constituents, including germacra-1(10)-5-dien-4-ol (60.0%), germacrene A (9.0%), germacrene D (7.0%), and bicyclogermacrene (2.0%) [16]. A doctoral thesis in the comparative biology of Catasetum presented (Z)-α-bergamotene, neryl acetate, and (E)-β-farnesene as the main components of C. barbatum sampled in the Amazonas state, Brazil [18]. This last sample of C. barbatum is more associated with the one analyzed in the present work due to the presence of (E)-β-farnesene, except for the significant content of trans-geranylgeraniol in the sample worked by us.

2.1.4. Catasetum ciliatum Barb. Rodr.

Botanical description: Epiphytic, erect, caespitose, ca. 38.0 cm long. Short rhizome, less than 1.0 cm between pseudobulbs. Caulomas thickened into pseudobulbs, aggregated, fusiform covered by leaf sheaths. Elliptical, semi-leathery leaves, five prominent veins. Inflorescence in a raceme, lateral; green peduncle, partially covered by tubular sheaths, ca. six flowers. Flowers (Figure 7) resupinate, greenish; sepals free from each other, dorsal elliptical; apex acuminate, elliptical-falcated laterals, apex acuminate; slightly oval petals. Lip green, elm-shaped, narrow base, adnate at the foot of the gynostemium, apex narrowly curved. Flowering in April and May [20].

Figure 7.

Figure 7

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Catasetum ciliatum. (Source Luiz Otavio Adão).

Geographic distribution: Not endemic In Brazil but found in areas of campinarana, rock fields, floodplain forests, sandbanks, and savannas, in the states of Amazonas, Amapá, Pará, Rondônia, Roraima, and Maranhão.

Two specimens of C. ciliatum were analyzed. Specimen Ccil-1 was sampled initially in the municipality of Prainha, and specimen Ccil-2 was collected initially in the locality of Lago Preto, municipality of Santarém, Pará state Brazil. Table 4 lists the constituents of their volatile concentrates.

Table 4.

Constituents identified in the volatile concentrates of two specimens of C. ciliatum flowers.

Constituents (%) RICal RILit Ccil-1 Ccil-2
Hexanal 795 801 a - 0.2
n-Octane 796 800 a - 0.2
Heptanal 898 901 a - 0.4
α-Pinene 929 932 a 10.5 4.8
Benzaldehyde 953 952 a 0.2
Sabinene 968 969 a 0.3 0.1
β-Pinene 973 974 a 0.9 0.3
Myrcene 987 988 a 0.7 0.2
α-Phellandrene 1003 1002 a 2.2 0.4
p-Cymene 1018 1020 a 0.1 0.1
β-Phellandrene 1025 1025 a - 2.4
1,8-Cineole 1027 1026 a 23.7 3.7
(E)-β-Ocimene 1043 1044 a 0.1 0.1
6,7-Epoxymyrcene 1092 1090 a 0.1 -
Linalool 1095 1095 a 0.1 0.1
n-Nonanal 1104 1107 a 0.1 0.6
(2E,4E)-Octadienal 1118 1113 b 0.1 -
trans-Limonene oxide 1136 1137 a 2.6 0.1
Benzyl acetate 1166 1167 b 11.8 22.8
Naphthalene 1175 1178 a 0.1 -
Terpinen-4-ol 1178 1180 b 0.6 -
α-Terpineol 1184 1186 a 0.2 -
cis-Dihydro carvone 1996 1991 a 0.4 -
trans-Dihydro carvone 1204 1200 a 0.1 -
cis-Carveol 1231 1232 b 0.1 -
Carvone 1242 1239 a 7.8 4.4
Geraniol 1251 1249 a 16.6 5.0
cis-Carvone oxide 1262 1262 b 14.3 10.1
2-Phenylethyl acetate 1261 1254 a 3.2 30.5
Geranial 1267 1264 a 0.2 0.1
Dihydrocarveol acetate 1311 1306 a 0.3 0.2
Geranyl acetate 1378 1379 a 0.4 0.9
n-Tricosane 2294 2300 a - 0.4
n-Tetracosane 2393 2400 a - 0.2
Behenic alcohol 2448 2456 c - 5.4
Monoterpene hydrocarbons 14.8 8.4
Oxygenated monoterpenes 67.5 24.6
Benzenoids/Phenylpropanoids 15.0 53.5
Fatty acid and derivatives 0.3 7.4
Total (%) 97.6 93.9
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RICal = Calculated Retention Index; RILit = Literature Retention Index; a Adams, 2007; b Mondello, 2011; c Nist, 2011. Bold = Main constituents. Unidentified minor constituents were 2.4% and 6.1%, respectively.

The two analyzed specimens of C. ciliatum were rich in oxygenated monoterpenes (67.5% and 24.6%), benzenoids/phenylpropanoids (15.0% and 53.5%), and monoterpene hydrocarbons (14.8% and 8.4%). There was a predominance of 2-phenylethyl acetate (3.2% to 30.5%), 1,8-cineole (3.7% to 23.7%), benzyl acetate (11.8% to 22.8%), geraniol (5.0% to 16.6%), cis-carvone oxide (10.1% to 14.3%), α-pinene (4.8% to 10.5%), and carvone (4.4% to 7.8%), analyzing both specimens (see Figure 8). The floral scents of C. ciliatum are being described for the first time.

Figure 8.

Figure 8

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Ion-chromatogram of the Catasetum ciliatum volatile concentrates.

2.1.5. Catasetum galeritum Rchb.f.

Botanical description: Epiphyte. Conical-fusiform pseudobulbs, compressed on the sides, ringed and furrowed. Leaves lanceolate-spatulate, acuminate towards the base, attenuated in canaliculate pseudo petiole, with five to seven longitudinal veins. Inflorescence from 20.0 to 25.0 cm, racemose, basal, pendant, and robust. Pedicel patent, arched, plump with pseudo-ovary. Flowers (Figure 9) are not resupinate and patent. Petals oblong-ligulate, sharp, erect, conniving with the dorsal sepal and embraced by its margins. Sepals are slightly convex and attenuated at the base. Very patent lip, somewhat reflexive, inferior, thickly fleshy, rigid, longer than the lateral sepals, with an oblong sack form protuberance, laterally compressed, entire, the sides erect over the sac projected forward. Fleshy column, elongated, at apex short conical rostrum, slightly curved. Antennae about 18.0 mm long, parallel, converging, with two yellow pollinia. The flowers of C. galeritum release an intense and sweet perfume, easily detectable by the human nose up to 2.0 m away [21]. Flowering in April.

Figure 9.

Figure 9

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Catasetum galeritum. (Source Luiz Otavio Adão).

Synonimy:Catasetum galeritum var. pachyglossum Rchb.f. [17].

Geographic distribution: Endemic in Brazil, occurs in riparian or gallery forests, Upland and floodplain forests, and broadleaf forests in the states of Amazonas, Pará, Tocantins, Maranhão, and Mato Grosso [17].

This C. galeritum specimen was sampled initially in the municipality of São Félix do Xingu, Pará state, Brazil, and the constituents of their volatile concentrate are listed in Table 5.

Table 5.

Constituents identified in the volatile concentrate of C. galeritum flowers.

Constituents RICal RILit %
n-Hexanol 861 886 a 0.1
Heptanal 902 901 a 0.1
Myrcene 987 988 a 0.4
Limonene 1026 1024 a 0.1
Sylvestrene 1027 1025 a 0.1
(Z)-β-Ocimene 1035 1032 a 0.1
(E)-β-Ocimene 1043 1044 a 1.6
Terpinolene 1085 1086 b 0.1
Linalool 1097 1095 a 34.9
allo-Ocimene 1128 1128 a 0.1
1,4-Dimethoxybenzene 1160 1161 a 54.1
Terpinen-4-ol 1180 1180 a 0.1
α-Terpineol 1195 1195 a 1.4
Nerol 1231 1229 a 0.3
Geraniol 1251 1249 a 0.9
Indole 1289 1290 a 5.2
7-epi-Sesquithujene 1390 1390 a 0.1
Monoterpene hydrocarbons 2.5
Oxygenated monoterpenes 37.6
Sesquiterpene hydrocarbons 0.1
Benzenoids/Phenylpropanoids 59.3
Fatty acid and derivatives 0.2
Total 99.7
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RICal = Calculated Retention Index; RILit = Literature Retention Index; a Adams, 2007; b Mondello, 2011; Bold = Main constituents. Unidentified minor constituents were 0.3%.

Benzenoids/phenylpropanoids (59.3%) predominated in the volatile concentrate of C. galeritum, followed by oxygenated monoterpenes (37.6%). The main constituents were 1,4-dimethoxybenzene (54.1%), linalool (34.9%), and indole (5.2%) (see Figure 10). A previous floral scent of another C. galeritum specimen, also occurring in the municipality of São Felix do Xingu, Pará state, Brazil, and visited only by male bees, was similarly composed of 1,4-dimethoxybenzene (85-94%), followed by minor amounts of linalool, indole, β-elemene, and (E)-caryophyllene [21].

Figure 10.

Figure 10

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Ion-chromatogram of the Catasetum galeritum volatile concentrate.

2.1.6. Catasetum gnomus L. Linden & Rchb.f.

Botanical description: Epiphyte. Pseudobulbs fusiform, erect, slightly compressed on the sides, long attenuated and acuminate, aggregated. Leaves oblong-lanceolate, 7 to 9 per pseudobulb, 3-veined, erect-patent. Inflorescence male basal, racemose, arched to pending. Bracts amplexicaul lanceolate, acuminate. Flowers (Figure 11) 5 to 15 non-resupinate, alternate on the rachis, somewhat inclined or drooping. Triangular floral bracts run to the pedicels. Pedicel cylindrical, sinuous. Dorsal sepal oboval-lanceolate, attenuated base, acuminate and acute apex; the sides oboval-lanceolate, slightly united at the base, apex very acuminate. Petals linear-lanceolate, erect, partially covered by the dorsal sepal and covering the column, oblique. Fleshy lip, with sack form protuberance (25.0 mm bristle), undulating and crenulated margins, sometimes serrated, internally under the column with a carina and around the thickened ostium, the anterior side always with the margins reclined downwards. Fleshy column, erect, triangular in cross-section, apex rostriform, threadlike, and long. Crossed antennas. Two yellow pollinia. Anther yellowish [17]. Flowering in February.

Figure 11.

Figure 11

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Catasetum gnomus. (Source Luiz Otavio Adão).

Synonimy:Catasetum gnomus var. phasma (Rchb.f.) Cogn., Catasetum heteranthum Barb. Rodr., Catasetum huebneri Mansf., Catasetum mocuranum Schltr., Catasetum negrense Schltr., Catasetum phasma Rchb.f.

Geographic distribution: Endemic in Brazil occurs in riparian or gallery forests, Upland and floodplain forests, and broadleaf forests in the states of Amazonas, Pará, and Rondônia.

This C. gnomus specimen was sampled initially in Manaus, Amazonas state, Brazil, and the constituents of its volatile concentrate are listed in Table 6.

Table 6.

Constituents identified in the volatile concentrate of C. gnomus flowers.

Constituents RICal RILit %
α-Pinene 929 932 a 2.2
α-Phellandrene 1004 1002 a 1.5
p-Cymene 1018 1020 a 1.5
Limonene 1026 1024 a 7.5
1,8-Cineole 1027 1026 a 2.7
Methyl benzoate 1090 1088 a 2.2
1,3,8-p-Menthatriene 1110 1108 a 0.5
cis-p-Menth-2-en-1-ol 1119 1118 a 1.2
trans-p-Mentha-2,8-dien-1-ol 1121 1122 a 2.8
trans-Limonene oxide 1136 1137 a 0.2
Methyl salicylate 1190 1190 a 17.0
cis-Piperitol 1197 1195 a 0.8
trans-Piperitol 1208 1207 a 0.8
Indole 1289 1290 a 1.6
δ-Elemene 1336 1335 a 0.4
α-Cubebene 1349 1349 a 0.9
Eugenol 1355 1357 a 0.6
α-Copaene 1374 1374 a 0.1
β-Elemene 1388 1389 a 0.8
(E)-Caryophyllene 1417 1417 a 3.6
trans-Muurola-3,5-diene 1450 1451 a 0.2
α-Humulene 1453 1452 a 1.3
trans-Cadina-1(6)-4-diene 1473 1475 a 0.2
Germacrene D 1479 1480 a 3.8
(E)-β-Ionone 1485 1487 a 0.8
δ-Selinene 1491 1492 a 0.2
epi-Cubebol 1494 1493 a 0.5
α-Muurolene 1496 1500 a 1.7
Bicyclogermacrene 1497 1500 a 0.7
(E,E)-α-Farnesene 1508 1505 a 0.8
γ-Cadinene 1514 1513 a 3.3
δ-Cadinene 1524 1522 a 10.3
trans-Cadina-1,4-diene 1532 1533 a 0.1
α-Cadinene 1537 1537 a 0.6
Germacrene D-4-ol 1574 1574 a 4.3
Caryophyllene oxide 1583 1582 a 0.2
epi-α-Muurolol 1641 1638 a 6.9
α-Muurolol 1646 1645 a 0.9
Cadin-4-en-10-ol 1656 1659 b 12.1
(Z)-α-trans-Bergamotol 1693 1690 a 0.6
Monoterpene hydrocarbons 13.2
Oxygenated monoterpenes 8.5
Sesquiterpene hydrocarbons 29.0
Oxygenated sesquiterpenes 26.3
Benzenoids/Phenylpropanoids 21.4
Total 98.4
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RICal = Calculated Retention Index; RILit = Literature Retention Index; a Adams, 2007; b Mondello, 2011; Bold = Main constituents. Unidentified minor constituents were 1.6%.

Sesquiterpene hydrocarbons (29.0%) predominated in the volatile concentrate of C. gnomus, followed by oxygenated sesquiterpenes (26.3%), benzenoids/phenylpropanoids (21.4%), monoterpene hydrocarbons (13.2%), and oxygenated monoterpenes (8.5%). The main constituents were methyl salicylate (17.0%), cadin-4-en-10-ol (12.1%), δ-cadinene (10.3%), limonene (7.5%), and epi-α-muurolol (6.9%) (see Figure 12). The floral scents of two other C. gnomus specimens grown in a greenhouse at the University of Miami, Florida, USA, were previously reported, showing methyl salicylate, α-pinene, 1,8-cineole, and methyl benzoate as their main constituents [16,19,22].

Figure 12.

Figure 12

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Ion-chromatogram of the Catasetum gnomus volatile concentrate.

2.2. The Catasetum Floral Scent Chemistry

The primary constituents found in the Catasetum flowers analyzed in this work were the monoterpenes linalool, 1,8-cineole, α-pinene, limonene, geraniol, carvone, and cis-carvone oxide; the sesquiterpenes 7-epi-1,2-dehydro-sesquicineole, (E,E)-farnesene, (E)-β-farnesene, δ-cadinene, epi-α-muurolol, and cadin-4-en-10-ol; the benzenoids anisyl butyrate, indole, benzyl acetate, 2-phenylethyl acetate, methyl salicylate, and 1,4-dimethoxybenzene; and the diterpene trans-geranylgeraniol. By analogy, consulting the literature, it was found that the floral aromas of 30 species of Catasetum (around 17% of existing) have already been chemically characterized. In these studies, 124 volatile compounds were reported, belonging to the following classes of compounds: monoterpenes (44), sesquiterpenes (26), irregular terpenes (1), aliphatics (14), aromatics (38), and N-bearing compounds (1). Individually, 1,8-cineole and α-pinene were the most reported, followed by β-pinene, (E)-dihydrocarvone, (E)-carvone epoxide, carvone, and p-cymene (10) [2,16].

The complexity of floral scents in the species of Catasetum investigated so far varies considerably. In the present work, more than 93% of the scent profile has been characterized, while the number of identified constituents varied from 1 in C. micranthum to 74 in C. uncatum [23,24]. This variation in scent floral complexity across Catasetum species certainly reflects an inherent characteristic for each species. As expected in angiosperms, floral scents of Catasetum are species-specific, although dominated by some significant constituents usually shared by several species [25]. Most Catasetum species have 2 or 3 main constituents that account for more than 70% of the fragrances. These constituents are potent attractants to many Euglossa and Eulaema bees, but the attractiveness to individuals and species is reduced as more components compose the mixtures so that specific scents attract only a few pollinator species [11,19].

The pivotal role of floral fragrances in pollinator shifts and as a reproductive isolating mechanism in Catasetum was previously highlighted [16]. However, floral scents may not be enough to assure the effective reproductive isolation in Catasetum. Sympatric species usually produce similar fragrances, thereby attracting the same pollinator species. In these cases, different reproductive isolating mechanisms (e.g., geographical, morphological/mechanical, temporal/seasonal), acting alone or together, will be necessary to contribute to or prevent the hybridization [16,19]. Presently, considering the well-defined separation of the pollinating genera of Catasetum and the higher sensorial similarity between the closely related bee species, have been speculated that the olfactory adaptations have shaped the evolution of floral fragrances of Catasetum due to the partitioning with pollinator’s bees, particularly from the genera Euglossa and Eulaema [16,19].

Therefore, pollinator affinity with phylogeny is correlated with differences found in floral aromas. More generally, the question is why flowers produce different odors or why mixtures of odors tend to be species-specific. The answer to this question demands more complex functional analyses, attributing phylogenetic, physiological, and ecological influences to the chemical variation of floral scents [25].

2.3. Catasetum Specimens’ Multivariate Analysis

The floral variability of samples of Catasetum volatile concentrates was evaluated using multivariate statistical analyses (PCA, principal component analysis; HCA, hierarchical cluster analysis) based on their classes of compounds. The percentage values of monoterpene hydrocarbons (MH), oxygenated monoterpenes (OM), sesquiterpene hydrocarbons (SH), oxygenated sesquiterpenes (OS), oxygenated diterpenes (OD), benzenoids/phenylpropanoids (B/P), and fatty acids and derivatives were obtained based on the GC-MS analyses of the volatile concentrate constituents. The data were used as variables (see Table 7).

Table 7.

Classes of compounds identified in Catasetum specimens used in the multivariate statistical analyses.

Classes of Compounds (%) Cala Calb-1 Calb-2 Cbar Ccil-1 Ccil-2 Cgal C.gno
Monoterpene hydrocarbons 36.9 8.7 7.9 0.5 14.8 8.4 2.5 13.2
Oxygenated monoterpene 57.0 36.7 52.4 0.2 67.5 24.6 37.6 8.5
Sesquiterpene hydrocarbons 2.2 1.0 5.2 16.4 1.0 - 0.1 29.0
Oxygenated sesquiterpene 1.2 30.4 20.8 2.1 - - 26.3
Oxygenated diterpenes - - - 62.0 - - - -
Benzenoids/Phenylpropanoids 0.3 16.1 7.6 11.8 15.0 53.5 59.3 21.4
Fatty acids and derivatives 0.9 4.8 2.6 4.3 0.3 7.4 21.4 -
Total (%) 98.5 97.7 96.5 97.3 97.6 93.9 99.7 98.4
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The HCA analysis (Figure 13) showed the formation of five groups. The first group comprised C. alatum and C. ciliatum-1 (I); the second group the two specimens of C. albovirens (II); the third group of C. gnomus (III); the fourth group of C. barbatum (IV); and fifth group by C. ciliatum-2 and C. galeritum (V).

Figure 13.

Figure 13

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Hierarchical cluster analysis (HCA) of the Catasetum volatile concentrates, based on their classes of compounds.

The PCA analysis (Figure 14) explained 69.5% of the data variability. The PC1 justified 35.32% of the data, showing negative correlations with monoterpene hydrocarbons (MH, λ = −0.52), oxygenated monoterpenes (OM, λ = −0.43), oxygenated sesquiterpenes (OS, λ = −0.12) and positive correlations with sesquiterpene hydrocarbons (SH, λ = 0.09), oxygenated diterpene (OD, λ = 0.28), benzenoids/phenylpropanoids (BZ-PP, λ = 0.46), and fatty acids and derivatives (FA, λ = 0.45). The PC2 clarified 34.3% of the data, showing a positive correlation with oxygenated sesquiterpenes (OS, λ = 0.32), oxygenated diterpene (OD, λ = 0.36), and sesquiterpene hydrocarbons (SH, λ = 0.56), and negative correlation with monoterpene hydrocarbons (MH, λ = −0.08), oxygenated monoterpenes (OM, λ = −0.42), benzenoids/phenylpropanoids (BZ-PP, λ = 0.35), and fatty acids and derivatives (FA, λ = −0.38). Similar to HCA, the PCA analysis confirmed the formation of five distinct groups.

Figure 14.

Figure 14

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Principal componente analysis (PCA) of the Catasetum volatile concentrates, Based on their classes of compounds.

Group I was characterized by oxygenated monoterpene (57.0–67.5%) and monoterpene hydrocarbons (14.8–36.9%). Group II was characterized by oxygenated monoterpenes (36.7–52.4%) and oxygenated sesquiterpenes (20.8–30.4%). Group III was characterized by sesquiterpene hydrocarbons (29.0%), oxygenated sesquiterpenes (26.3%), and benzenoids/phenylpropanoids (21.4%). Group IV was characterized by oxygenated diterpenes (62.0%). Group V was characterized by benzenoids/phenylpropanoids (53.5–59.3%) and oxygenated monoterpenes (24.6–37.6%).

3. Materials and Methods

3.1. Plant Material

The orchids Catasetum alatum, C. albovirens, C. barbatum, C. ciliatum, C. galeritum, and C. gnomus (Figure 1, Figure 2, Figure 3, Figure 4, Figure 5 and Figure 6), which provided the flowers for this work, are live plants cultivated in pots containing charcoal and wood shavings, existing in the private nursery of Mr. Luiz Otávio Adão Teixeira, located in the Amazon Garden Condominium, BR-316, km 6, 67015-795 Ananindeua, PA, Brazil (coordinates: 1°22′20.96″ S/48°23′34.14′′ W). These orchid specimens were previously sampled in various localities and cities of the Brazilian Amazon, as already described for each one in the Results. Each plant exemplar (exsiccate) was deposited in the Herbarium of Emílio Goeldi Museum, Belém, Para state, Brazil. The orchid flowers were collected during the flowering period, at 6 am, to extract their volatile constituents.

3.2. Obtaining and Analyzing Volatile Concentrates

The orchid flowers were subjected to micro distillation-extraction in a Likens & Nickerson-type apparatus (3 flowers each, 15 g in total, 2 h, duplicate) to obtain their volatile concentrates, using n-pentane (99% HPLC grade, 3 mL) as the solvent [26].

The volatile concentrates of orchids were submitted to GC and GC-MS analysis. It was performed on a GCMS-QP2010 Ultra system (Shimadzu Corporation, Tokyo, Japan), equipped with an AOC-20i auto-injector and the GCMS-Solution software containing the Adams (2007), Mondello (2011), and Nist (2011) libraries [27,28,29]. A Rxi-5ms (30 m × 0.25 mm; 0.25 μm film thickness) silica capillary column (Restek Corporation, Bellefonte, PA, USA) was used. The conditions of analysis were as follows. Injector temperature: 250 °C; Oven temperature programming: 60–240 °C (3 °C min−1); Helium as the carrier gas, adjusted to a linear velocity of 36.5 cm s−1 (1.0 mL min−1); split mode injection (split ratio 1:20) of 1.0–2.0 µL of the n-pentane solution; electron ionization at 70 eV; ionization source and transfer line temperatures of 200 and 250 °C, respectively. The mass spectra were obtained by automatically scanning every 0.3 s, with mass fragments in the 35–400 m/z. The retention index was calculated for all volatile components using a homologous series of C8-C40 n-alkanes (Sigma-Aldrich, Milwaukee, WI, USA) according to the linear equation of van den Dool and Kratz (1963) [30]. Individual components were identified by comparing their retention indices and mass spectra (molecular mass and fragmentation pattern) with those existing in the GCMS-Solution system libraries [27,28,29]. The quantitative data regarding the volatile constituents were obtained using a GC2010 Series gas chromatograph, operated under similar conditions to those of the GC-MS system. The relative amounts of individual components were calculated by peak-area normalization using a flame ionization detector (GC-FID). Chromatographic analyses were performed in duplicate.

3.3. Multivariate Statistical Analysis

Principal Component Analysis (PCA) was applied to verify the interrelationship of the samples of volatile concentrates analyzed with the classes of identified compounds, monoterpene hydrocarbons (MH), oxygenated monoterpenes (OM), sesquiterpene hydrocarbons (SH), oxygenated sesquiterpenes (OS), oxygenated diterpenes (OD), benzenoids/phenylpropanoids, and fatty acids and derivatives. The data matrix was standardized for multivariate analysis by subtracting the mean and dividing it by the standard deviation. Hierarchical Cluster Analysis (HCA), considering the Euclidean distance and complete linkage, was used to verify the similarity of the samples based on the distribution of the constituents selected in the PCA analysis (Software Minitab, free version 390, Minitab Inc., State College, PA, USA) [31].

4. Conclusions

In conclusion, the present study showed that previous reports were not found in the literature concerning the chemotaxonomy of the Catasetum species. Thus, considering their classes of compounds, Catasetum albovirens, C. gnomus, and C. barbatum can be distinguished from the other studied species, while C. alatum, C. galeritum, and C. ciliatum showed the same primary compound classes. Also, there are two chemotypes of C. ciliatum, the first one rich in oxygenated monoterpene (67.5%) and the second rich in benzenoids/phenylpropanoids (53.5%). Thus, we think these findings could contribute to a better understanding of the chemical profiles of Catasetum species.

Acknowledgments

Authors are grateful to CNPq and CAPES, scientific research agencies of the Brazilian Government for their financial of fellowships support.

Author Contributions

Conceptualization, J.G.S.M. and E.H.A.A.; methodology, J.G.S.M. and F.M.d.V.; software, P.L.B.F.; formal analysis, F.M.d.V., E.H.A.A. and P.L.B.F.; resources, L.O.A.T. and E.H.A.A.; data curation, F.M.d.V. and L.O.A.T.; writing—original draft preparation, F.M.d.V. and J.G.S.M. writing—review and editing, F.M.d.V., E.H.A.A. and J.G.S.M.; project administration, J.G.S.M. and E.H.A.A. All authors have read and agreed to the published version of the manuscript.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

Funding Statement

This research received no external funding.

Footnotes

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