Cistus albidus L.: Comparison
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Cistus albidus is one of the approximately 20 species of the Cistus genus. The genus’ name is derived from the ancient Greek term kistos. It is supposed that the name alludes to the woody capsule fruits. Evergreen in its Mediterranean homeland and between 50 and 250 centimeters tall, this shrub is called albidus, not because of the colour of its flowers, but because its leaves are finely covered with white hair (trichomes).

  • phytochemistry
  • pharmacology
  • polyphenols
  • terpenes
  • traditional uses

1. Botanical Characteristics

From the morphological point of view, C. albidus is characterized by having five sepals, five pink to purple petals, up to 150 yellow stamens, pollen with a thin exine up to 1.4 μm thick, a long style that reaches or exceeds the stamens, and three cellular polysperm capsules. The hermaphroditic, actinomorphic, and hypogynous flowers, which appear from February to July, normally reach a diameter of four to six centimeters and develop individually or in umbels of usually five to seven [1]. The five sepals are ovate-lanceolate and hairy. The five petals, on the other hand, are delicate and slightly wrinkled. The flowers open in the morning and after a few hours the plant loses its petals. The flowers rarely last more than a day. A single adult bush can produce more than 1000 flowers per flowering period, depending on age [2].
The ovate-lanceolate leaves are arranged opposite each other and are usually 20–50 mm long and 8–30 mm wide; however, specimens with leaves exceeding 100 mm long and more than 50 mm wide have also been found by the authors. They are sessile, with a smooth margin, but may occasionally have a slightly wavy edge. Foliar veins are composed of three to five principal veins with a strong central vein. Adaxis veins are sunken, while veins on the abaxial surface are raised.
Typical  Mediterranean  landscape  with  a  predominance  of  C.  albidus,  called  jaral  (left).  Detail of flowers and leaves of C. albidus in spring (right).
Due to its morphological adaptation to an extremely dry climate within Mediterranean regions and a pronounced resistance to abiotic stress in general, C. albidus could be considered a malacophilous xerophyte. During dry periods, these plants reduce the growth of relatively long and wide hairy leaves until only short, narrow leaves remain. At the same time, the hairiness (trichomes) of the leaves of these plants is increased. In general, these processes significantly reduce respiration, which is an effective protection mechanism against dehydration [3][4].

Vegetative Development

C. albidus has developed mechanisms that allow it to withstand severe summer droughts. These mechanisms consist in part of a reduction in leaf area and angle [3], combined with an increase in root mass per leaf area and modification of stomatal conductance [5]. On the other hand, the link between tocopherols and jasmonates appears to be primarily responsible for the regulation of biotic and abiotic stress responses [6]. It was observed that, under water stress, C. albidus increases enzymes related to redox homeostasis, such as oxidized ascorbate reductase, glyoxalase, superoxide dismutase, and isoflavone reductase, which was related to a reduction in oxidative stress in C. albidus exposed to drought and the ability to recover quickly after re-irrigation [7]. The interaction of these mechanisms allows this species to resist the adverse Mediterranean climate conditions with only little photoinhibition [6].
Furthermore, C. albidus belongs to the nanophanerophytes (a subgroup of phanerophytes). These are plants whose overwintering buds are above the level of the snow cover. In contrast to the macrophanerophytes, they do not rise above the level of the surrounding vegetation. They are therefore partially sheltered from the wind. Due to this fact, a more than 2 m high specimen was discovered in the Valle y Carrascoy Regional Park in Murcia, surrounded by shrubs up to 3 m high.
The vegetative development of this species, which normally lives for about 14 years [8] and was found to reach 17 [9] or even 25 years [2], is characterized by two types of lateral shoots, dolichoblasts and brachyblasts. Dolichoblasts are long shoots with large leaves, which are produced when climatic conditions are benign (availability of water and absence of frost), which is usually between the end of February to May and from September to December. Brachyblasts are short shoots that develop throughout the year in the axils of leaves of dolichoblast shoots [10]. The fall of the leaves of this marcescent species is acropetic.
Sexual reproduction begins at about the age of one year. The flowers of this partially self-incompatible species [11] normally last around 12 h but may last up to two days on the plant, especially in rainy weather with high relative air humidity. This seems to be due to the fact that the apoidea, its main pollinators [11], do not fly in humid environmental conditions. It has been further shown that zeatin is the substance that modulates the speed of floral development, depending on the age of the plants [12].
Fruiting takes place from May to August. The capsules contain an average of about 80 seeds, with exceptions found by the authors from fewer than 10 seeds to more than 140, and generally mature from August to December [10][11], but in warmer regions such as the Spanish Levant, for example, the first capsules usually mature at the end of May. Mature capsules spread their seeds close to parent plants as they lack expansion mechanisms. Studies suggest that C. albidus seeds experience a combination of physical and physiological dormancy [13]. Although physical dormancy was broken and water was available, the seeds seemed able to partially control their dormancy and germination capacity [13]. Under optimal conditions, germination takes between five and ten days and is epigeal [14].
Like other plants typical of fire-prone regions, C. albidus is generally considered pyrophytic [15], especially since the heat generated by fire is thought to facilitate breaking physical dormancy due to the hard seed coat [8][16][17]; thus, it is one of the first shrubs to emerge after a fire. Development is therefore rapid within the first five years and then progressively slows down [8]. However, the scarification of the seeds, by soil particles, (through dragging by water flow) also softens the hard cover of the seeds, making them permeable to water [18], thus overcoming physical dormancy [18][19]. In addition, it is common to find this species along the edges of watercourses with temporary flows. This seems to be its dispersal strategy since forest fires do not facilitate the spatial expansion of this species. Very specific conditions must be met for the seeds to viably survive forest fires and also break the integument. For this reason, C. albidus could be considered an opportunistic pioneer plant.
Regarding the influence of the soil on the development of C. albidus, together with C. creticus, it is the only taxon of the purple-pink clade capable of growing independently in calcareous and acidic soils. However, C. albidus grows best on calcareous soils in Mediterranean climates [20][21]. Studies reported that no significant qualitative or quantitative differences were found in the polyphenolic profile between the cultivation of C. albidus in different types of soil [20][22], while the concentration of terpenes was influenced by soil conditions, showing lower yields in calcareous soils [23]. However, higher concentrations of polyphenols were not associated with lower soil fertility [24]. This suggests that the genetic influence of this species on the biosynthesis of phytochemicals may be stronger than the influence of soil parameters. This was confirmed by a recent study, where C. albidus exhibited a low translocation of Pb and Cd to aerial parts from heavy-metal-contaminated soil [25], making this species also suitable for plantations under problematic soil conditions.

2. Phytochemical Constituents

The main constituents of C. albidus-derived products belong to the groups of terpenes and polyphenols. Other organic compounds have also been detected. To date, more than 200 secondary metabolites have been reported in C. albidus samples. In this review, 153 terpenoids, including 31 monoterpenes, 109 sesquiterpenes, 9 diterpenes, and 3 tetraterpenes, and their respective derivatives were found. In addition, 58 polyphenols, including 19 phenolic acids, 17 flavonols, 11 flavanols, 3 ellagitannins, 3 anthocyanins, 2 flavones, 1 anthocyanidin, 1 flavanone, and 1 hydrolysable tannin, were found. Moreover, 8 fatty acids, 7 alkanes, and various other compounds were found in the literature and discussed in the present study.
The irregular presence of reported compounds–analyses were often very heterogeneous—is possibly due to seasonal variation and the analytical methods used. Secondary metabolites reported so far have been determined under a wide variety of conditions, making it sometimes difficult to compare among the studies. For example, some metabolites, such as punicalagin derivatives or some diterpenes, were only found in a small number of studies [20][26]. The results depend on multiple factors, such as the method of analysis, the season and hours of the day of collection, and the type of processing, among others, and some of these factors are not detailed in many studies. However, on the other hand, there are a number of compounds that practically all authors found in significant amounts, being thus characteristic of this species. These more common compounds will be highlighted in the following sections.
The various compound structures detected in C. albidus are described below, headed by the terpenes and paying particular attention to the essential oils (mono- and sesquiterpenes). Phenylpropanoids detected in essential oils are also briefly discussed. Furthermore, di- and tetraterpenes are described. The second large group of substances, polyphenols, are examined more closely, especially flavonols, flavanols, ellagitannins, and phenolic acids. The carbonyl compounds and alkanes found so far are then listed. Finally, proven phytohormones and various fatty acids are described. However, the latter is not part of the secondary metabolism but is included here for its supposed importance as a potential bioavailability enhancer.

2.1. Terpenes

2.1.1. Mono- and Sesquiterpenes from the Essential Oils

Terpenes, a very large but heterogeneous group of naturally occurring secondary metabolites in C. albidus, represent the group with the most compounds identified in this species. Among them, the most abundant were the sesquiterpenes; they were, in addition, the largest class of identified compounds in C. albidus. While monoterpenes were found to contribute, to a certain extent, together with aldehydes, to the characteristic odor of this species (they are among the main components of floral aromas), the sesquiterpenes play a signaling role in the defense mechanisms of this species, acting as herbivore repellents or through the attraction of predators. Diterpenes are also synthesized for defense purposes and serve as precursors for vitamins and hormones such as tocopherols and gibberellins. Finally, tetraterpenes contribute to the pigmentation of flowers and fruits, playing an essential role in the pollination and distribution of seeds. As an antioxidant, it protects C. albidus from oxidative stress caused by adverse growing conditions [5].
The ISO definition for essential oils is “Product obtained from a natural raw material of plant origin, by steam distillation, by mechanical processes from the epicarp of citrus fruits, or by dry distillation, after separation of the aqueous phase—if any—by physical processes” [27].
Essential oils from fresh aerial parts of C. albidus were generally obtained in low yields of 0.01–0.1% (w/w) [28][29][30] by steam distillation. The seeds, in particular, contain very small amounts of essential oil, sometimes insufficient to be analyzed, with a yield of less than 0.01% [30]. The concentration of terpenes depends fundamentally on soil conditions (the more calcareous, the lower the yield), climatic factors, and the season [23]. Analysis of seasonal variation in terpene composition shows strong interannual variability, with the highest emission rates in autumn and spring and the lowest in summer and winter, leading to maximum values of stored terpenes in autumn and winter, while the spring and summer values showed minimum levels [29]. Table 1 shows the list of the terpenoids identified in C. albidus samples, including information about their previously published pharmacological activity. The compounds most frequently found in the analyses of the extracted terpenes (w/w), and therefore representative of this species, whether in leaves, pollen, flowers, flowering tops, or stems, are α-zingiberene (7.4–20.7%), aromadendrene (1.0–10.6%), ar-curcumene (8.3–13.2%), and germacrene D (1.0–7.9%) [28][30][31][32][33][34][35]. Among the terpenes in leaves, flowering tops, and flowers, monoterpenes were only present in small quantities and sometimes only in traces, while sesquiterpenes were the most abundant [28][30][31].
Table 1. Identified terpenes in Cistus albidus. Table includes the structure for each compound along with the references in which it was identified and its pharmacological activity (including the references for this activity). 🌱: aerial parts, including leaves and twigs; ✿: flowering tops, flowers, petals, and sepals; 𐩕: pollen. n/a: reliable data are not available.
The following quantities refer to the w/w of the extracted oil. Oxygenated sesquiterpenes ranged from 44.8% in aerial parts (twigs, leaves, flowers) [28] to 67.1% in leaves [31]. Hydrocarbon sesquiterpenes were found from 22.5% in flowers [31] to 48.6% in aerial parts including flowers [28]. Within representative sesquiterpenes in leaves, α-zingiberene is the most abundant and was extracted from 5.9% [31] to 14.8% [30], followed by α-bisabolol with values ranging from 1.9% [30] to 11.4% [28]. Further ar-curcumene was obtained from 8.3% [28] to 10.6% [30], and β-bourbonene showed a presence from a residual 0.1% [30] up to 8.7% [28].
The essential oil compositions of the aerial parts (stems and leaves) of C. albidus showed only quantitative differences. However, the flowers’ (petals’) essential oil has a different composition, with mainly α-zingiberene, α-cadinol, ar-curcumene, and δ-cadinene [30][31], while the composition of the isolated pollen contained α-zingiberene, δ-cadinene, and germacrene D within the most abundant compounds [31].
Since the analyzed samples come from different places with different climatic and soil conditions, were collected on different dates, and were sometimes analyzed by different methods, comparison of their compositions is only possible to a very limited extent. In addition to these limitations, it must also be taken into account that the species of the Cistus subgenus hybridize with each other, which may also have an impact on the composition of the synthesized compounds if species purity has not been ensured beforehand.

2.1.2. Phenylpropanoids from the Essential Oils

Phenylpropanoids are compounds that are built from an aromatic benzene ring and a chain of three carbon atoms and often have hydroxyl and methoxy groups on the aromatic ring. Many phenylpropanoids are natural substances that are formed in plants and microorganisms through the shikimate biosynthetic pathway, with phenylalanine and tyrosine as intermediate compounds [36]. In addition to terpenes, phenylpropanoids are a frequent component of essential oils and represent the majority of natural phenolic substances or their precursors. The phenolpropanoids identified so far in C. albidus are eugenol [31][35][37] and chavicol [32].

2.1.3. Diterpenes

As for the diterpenes present in C. albidus, these are not usually detected in most analyses, because they belong to the non-volatile terpenes. This is mainly because the analytical methods described are not suitable for detecting non-volatile substances and not because of the absence of these compounds. The diterpenes detected so far are geranyl linalool, geranyl α-terpinene, geranyl p-cymene and 13-epi-mannoyloxide [35], methyl neoabietate [29], 15,16-dinorlabd-8(20)-en-13-one, manool [38], and manoyl oxide [39]. The latter was found in the aerial parts, including the stems, unlike 15,16-dinorlabd-8(20)-en-13-one and manool, which were obtained only from the leaves.

2.1.4. Tetraterpenes

Tetraterpenes are vital for plant growth, protection against stress, and successful reproduction. So far, lutein, neoxanthin, and zeaxanthin have been identified in C. albidus [4].

2.2. Phenolic Compounds

Phenolic compounds are based on the phenol structure. In general, these compounds can be divided into seven subgroups: simple phenols, hydroxybenzoic acids, hydroxycinnamic acids, coumarins, flavonoids, lignans, and lignins [40]. The concentration of these phenolic substances in plant foods depends, in part, on the plant species, the climate, and the degree of maturity [41]. In the present work, the analytical focus of phenolic compounds lies on the group of hydroxybenzoic acids (basic structure C6-C1), hydroxycinnamic acids (basic structure C6-C3) (Figure 1), and flavonoids (basic structure C6-C3-C6) as they are the most frequent polyphenolic groups present in C. albidus samples (Figure 6).
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Figure 1. Structures of hydroxybenzoic and hydroxycinnamic acids.
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Figure 6. Basic structure of flavonoids with their three characteristic rings which are formed by different biosynthetic pathways. The B ring is derived from the shikimate pathway via phenylalanine.
In general terms, the polyphenolic composition of C. albidus, is very similar to that of other members of the Cistus subgenus, such as C. crispus and C. × incanus (hybrid of C. albidus × C. criticus) [20]. A semi-quantitative analysis of the composition of extracts from C. albidus, C. clusii, C. ladanifer, and C. salviifolius revealed small differences between them [37] and a series of substances that occur exclusively in C. albidus, namely caftaric acid, prunin, and 5-O-caffeoylquinic acid glucoside [42].

2.2.1. Flavonoids

Flavonoids contribute to overall fruit color and flavor in plants [40]. In the form of flavones, they are responsible for the yellow hues of the inner petals in the flowers and of the stamens and, in the form of anthocyanidins, for the purple-pink colored petals of C. albidus. Flavones often appear as co-pigments of anthocyanins. The interaction of both types of dye explains the simultaneous appearance of yellow and red in different flowers. The flavonoids found so far are flavonols, flavones, flavanols, and tannins (Figure 2).
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Figure 2. Structure of flavonoids with their three characteristic rings.
Flavonols and flavones occur in C. albidus’ aerial parts as free algycones and glycosides. They are responsible for yellow color nuances and are usually tasteless. Flavonols are distinguished from flavones by the presence of a 3-hydroxyl group (Figure 7). Phenolic substances of the flavonol subclass are present in all plant organs of C. albidus. Characteristic representatives of these compounds in C. albidus are kaempferol, quercetin, myricetin, myricitrin (myricetin-3-O-rhamnoside), and quercitrin (quercetin-3-O-rhamnoside) [20]. High contents of myricetin glycoside (7 mg/g dry weight) were detected in C. albidus aerial parts, with myricetin-3-O-rhamnoside being the primary derivative of myricetin with 83% of total myricetin composition, followed by quercetin glycoside (2 mg/g dry weight), with quercetin-3-O-rhamnoside being the most abundant derivative of quercetin, constituting 80% of the total quercetin composition [26]. The only flavones detected so far are diglycosylated apigenin [20] and the isoflavone glycitin 6″-O-malonate [42].
Flavanols are found predominantly in the leaves of C. albidus and contribute particularly to the astringent taste of extracts. Compounds belonging to this subclass have two asymmetrically substituted carbon atoms and can therefore exist as diastereomeric 5,7,3-,4-tetrahydroxyflavanols, catechin and epicatechin. A third hydroxyl group on ring B also results in 5,7,3,4,5-pentahydroxyflavanol gallocatechin, or correspondingly epigallocatechin (Figure 7). Among the polymeric flavanols, the most relevant compounds in C. albidus are prodelphinidins such as (epi-)gallocatechins. Procyanidins are other representative flavanols contained in C. albidus leaves. Within these oligomeric compounds, (epi-)catechins are most common in C. albidus aerial parts [20]. However, combinations of prodelphinidins and procyanidins have also been detected. So far, the following flavan-3-ol compounds have been found: (+)-catechin, (−)-epicatechin, (−)-(epi)gallocatechin, (−)-(epi)gallocatechin-(epi)catechin dimer, (−)-(epi)gallocatechin, and (−)-(epi)gallocatechin-(epi)gallocatein dimer [20][43].
Tannins are water-soluble, slightly acidic oligomers of polyphenols. They are able to form water-insoluble complexes with protein molecules. In the past, this property of C. albidus was used to tan animal skin in leather production [44]. Based on the chemical structure of the monomeric building blocks, tannins present in C. albidus could be divided into two groups, the condensed and the hydrolyzable tannins.
The first group includes the proanthocyanidins (flavanols) already described, which are also known as condensed tannins. They consist of polymerized flavonoid phenols, such as catechins, epicatechin, anthocyanins, and so on. They are correspondingly polymers whose monomeric units consist of phenolic flavans, mostly catechin (flavan-3-ol).
The second group represents hydrolyzable tannins, which are hydrolyzed by the action of acids. These compounds exist as various polyhydroxy compounds, for example as sugar esterified with a phenolic acid [40]. Within this group, hexahydroxydiphenoyl-D-glucose (HHDP-Glc) was detected in C. albidus [20]. When the phenolic acid is gallic acid, the compound is called gallotannin. If, on the other hand, esterification with hexahydroxydiphenic acid occurs, this compound is called ellagitannin. Ellagitannins were not found in C. albidus aerial parts, except for a residual presence of glucogallin, pedunculagin, and punicalagin gallate [20][26].

2.2.2. Phenolic Acids

Phenolic acids are understood as the hydroxylated derivatives of benzoic acids (hydroxybenzoic acids) and cinnamic acids (hydroxycinnamic acids). Their highest concentration in plants is found in the outer leaves. In C. albidus aerial parts, glucogallin [20][26] and gallic acid [20][45] were found. Within the category of phenolic acid derivatives, 5-O-caffeoyl quinic acid glucoside, caffeoylquinic glycoside [42], and uralenneoside and rhamnoside of hydroxyferulic acid [20] have also been detected.

2.3. Carbonylic Compounds

Aldehydes are odoriferous aromatic substances in plants. These often arise from substances containing linolenic acid during harvesting, crushing, or preparation [46]. The aliphatic aldehydes, octanal [31], nonanal, and decanal [31][35], were exclusively identified in pollen and may be responsible for the typical sweet smell of the flowers [47]. On the other hand, tetradecanal, undecanal, and dodecanal were present in the aerial parts [35]. These compounds may contribute to the typical sweetish odor of C. albidus with its undertone of oranges, lemons, and roses [47][48].

2.4. Phytohormones and Vitamin E

Tocopherols and tocotrienols are also present in leaves and seeds. More than 75% of the vitamin E present in the seeds was in the form of α-tocopherol, followed by α-tocotrienol and γ-tocopherol [4][13][49], which is the immediate precursor of α-tocopherol. Phytohormone and vitamin studies further revealed the presence of the jasmonates 12-oxo-phytodienoic acid (OPDA), jasmonic acid (JA), and jasmonoyl-isoleucine (JA-Ile) and plastochormanol-8 [6], carotenoids, and abscisic acid, with α-tocopherol being the most abundant [2]. A negative correlation was revealed between vitamin E and OPDA accumulation in C. albidus under winter conditions, while a positive correlation was found between JA and α-tocopherol [6]. A significant positive correlation was also detected between hydration and total leaf chlorophylls due to the protection mechanism of tocopherols from the photosynthetic apparatus. Therefore, higher levels of α-tocopherol were observed under abiotic stress conditions and when the leaves showed an orientation more perpendicular to the solar rays [2][3][6][50].
Drought stress can induce an increase in the concentrations of abscisic acid and H2O2 in the leaves, inducing an increase in ascorbic acid, maintaining and even decreasing the oxidative state of ascorbate, thus protecting plants from oxidative damage [5][51]. In addition, cytokinins that act as nitric oxide scavengers and are involved in the modulation of the abscisic acid response have been reported [4].
C. albidus seeds obtained from mature plants showed higher concentrations of α-tocopherol, JA, and salicylic acid than those obtained from younger plants. Auxin (indole-3-acetic acid) content was also significantly higher in seeds from older plants. Gibberellic acid GA4 and its precursor GA24 were also found in seeds [2]. No differences were detected between the concentration of cytokinins in seeds from older and younger plants, except for zeatin, which was significantly higher in seeds from older plants. Zeatin was the main form of cytokinin found in the seeds of C. albidus [2].

2.5. Alkanes

Among the volatile compounds isolated from aerial parts of C. albidus, tricosan [35], tetracosan [29], pentacosan [23], octacosan [29], and docosan [23][29] were found. n-Tridecane was present in petals, and n-tetradecane was identified in both petals and pollen, while n-hexadecane was detected only in pollen, and n-pentadecane was found in leaves [23][29][35].

2.6. Other Compounds: Fatty and Carboxylic Acids

Although fatty acids are products of the primary metabolism, they are described here for the role they may play in the bioavailability of pharmacologically active compounds, as described below. Among the fatty acids found in the aerial parts of C. albidus are tetradecanoic, primaric and pentadecanoic acid [29], nonanoic acid [38], palmitic acid [35], and butanoic acid [31]. The fatty acid composition of the seeds showed significantly higher levels of polyunsaturated fatty acids as well as very-long-chain saturated fatty acids for older plants due to their higher levels of linoleic acid [2]. In addition, the carboxylic acids methacrylic acid [38] and quinic acid [37][42] were identified.

3. Preparation Methods of the

C. albidus

Extracts 

Studies of the pharmacological properties of traditional medicines based on C. albidus preparations are related to the presence of terpenoids and polyphenols. In order to understand the use that has been given to C. albidus traditionally, it is necessary to first review the preparation methods used in popular medicine of this plant due to their influence on the pharmacological effect. 6.1. Traditional Preparations For the different applications, traditionally, only the aerial parts of C. albidus were harvested, mainly the leaves, but also flowers, flower buds, and to a lesser extent stems. The traditional preparation of C. albidus varies from an infusion to a prolonged decoction, while the dose usually used is around 3 g per 100 mL of water, taking a cup (150 mL) two or three times a day [10]. Within traditional preparations, decoction is the most used technique. It consists of boiling the plant material for a certain period of time and letting it rest afterwards. This method is primarily suitable for thermostable and water-soluble phytochemicals. During decoction, several compounds undergo chemical modifications. For example, catechins undergo epimerization, which is a change in their configuration relative to one of their stereogenic centres. Epimers, specifically epicatechins and epigallocatechins, have been shown to have important health benefits. It has been found that this epimerization occurs more readily in water with alkaline pH values than in purified water [260]. In addition, it has been shown that at temperatures greater than 98ºC, epimerization occurs faster than its degradation [261], so it can be deduced that the traditional preparation of C. albidus is the most effective way to extract catechins and their epimers. However, for green tea, the levels of epicatechin, epicatechin gallate, epigallocatechin, and epigallocatechin gallate were reported to increase only during the first 3 to 5 min of preparation (infusion at 85ºC), and the proportion of these flavonoids decreased as time increased. In contrast, another study found that levels of catechin, gallocatechin, and gallocatechin gallate increased continuously with the length of preparation time [262]. Taking these results into account, the pharmacological activities referred to in traditional use could be optimized by limiting the decoction time. Nonetheless, thermolabile compounds are lost in the decoction process. As a result, monoterpenes should not be contained in the resulting extract. Sesquiterpenes, however, would not be affected by extracting temperatures around 100 degrees but by low solubility in water due to their lipophilic character. It can therefore be assumed that terpenes play a minor role in the traditional decoction of plant material. On the other side, probably in order to use the entire compound spectrum of the plant, based on both terpenes and polyphenols, the dried and crushed leaves sometimes were used directly (orally) [9,263–266]. This usage ensures that the resulting medicine is rich in polyphenols terpenes and other volatiles. However, a loss of several terpenes and oxidative reactions could be induced by the drying process, as reported for other species as Cannabis sativa [267,268].

4. Therapeutical Uses

4.1 Traditional Uses

Plant resources have always been an integral part of human society throughout history. Until the middle of the last century, traditional medicines provided an alternative and inexpensive source of primary health care for the rural population. However, with access to synthetic drugs, a large number of medicinal plants became obsolete, the memory of which in the population, after only two generations, is being lost. One of these medicinal plants is C. albidus, which has been used in traditional folk medicine for a variety of illnesses [10,286–288], especially for the treatment of fever, diarrhea and other gastrointestinal illnesses [8], skin diseases, rheumatism, and various inflammatory diseases [182]. For the sake of completeness, it is mentioned here that C. albidus has also been used as a tanning agent [181], as an insect repellent, and as a substitute for tobacco, highly appreciated, moreover, for its hypotensive effect [49,288,289]. The decoction of leaves was traditionally used in the Spanish Levant as a tranquilizer, in the Baixa Plana as a sedative [10], and as a remedy against Parkinson’s symptoms in Mallorca [290,291]. To relieve toothache, mouthwashes were made with a decoction of its leaves and flowers. A sip of the resulting liquid, once cold, was kept in the mouth for some time [266,292–294]. In addition, the decoction of the aerial parts was used as an external antiseptic, for wounds and skin infections [293–296]. In the Spanish Basque Country, several uses were reported. For example, decoction was applied for the treatment of ulcers and for the treatment of gangrene, and fresh leaves were used directly on the wound for disinfection [297]. In the Mediterranean region, the decoction of the aerial parts (leaves, stems, and flowers) has been used to regulate blood pressure [298,299]. It has also been a frequent remedy for hemorrhoids and to treat bruises and varicose veins [290]. The decoction of flowers and leaves has also been popularly used as an analgesic for oral infections [293] and for hepatoprotection in Granada and Mallorca [290,298]. The decoction of the fresh aerial parts, including the flowers, was used as a remedy against colds and flu infections, and against bronchitis [9,290,299] and whooping cough [10]. In the Spanish peninsula, C. albidus decoction has also been used as a remedy for osteoarthritis in the province of Jaen [266] and for rheumatism in the Valencian community and the Province of Jaen [292,300]. In addition, it was used as an external antiseptic for wound healing and skin infections in the provinces of Castellon, Mallorca, and Almería [10,290,293], and in Morocco [263,265]. In Sardinia (Italy), a traditional use is reported in poultices and ointments, which were applied directly to the wound [301]. In cases of gastrointestinal infections, in Almería (Spain), an infusion of dried leaves was prepared to reduce abdominal pain [293,298]. Against colic, in Castilla-La Mancha and Murcia (Spain) an infusion of young and tender shoots was administered, but it was also supplied by oral ingestion of the powder of dry leaves for treatment [9]. The dried leaf powder also served as an antidiarrheal in Jaen [266]. Infusions of fresh flowers and leaves have been used as an antiseptic for the urinary tract in Murcia [302] and also as an anti-inflammatory for orchitis in Valencia [303].

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