The search for new bioactive compounds from the plant kingdom is increasingly gaining the interest of scientific community. In fact, nutraceutical formulations could help in preventing a large number of the diet-associated chronic diseases rapidly emerging in Western countries, including cancer, type 2 diabetes, obesity, and various inflammatory conditions [1
]. International agencies strongly encourage the development of high quality, plant-based natural preparations to face such conditions, since this approach is supposed to present fewer adverse effects and be less expensive than common synthetic drugs [1
]. The cultivation of such plants, especially if they are endemic, can represent a considerable source of income in developing countries. Similarly, the discovery of natural remedies has also gained a lot of attention in recent decades in the cosmetic sector, even if, in some cases, modern science had not yet confirmed the traditional uses [2
is a typical example of a plant well known in ethnopharmacology but almost completely forgotten, as ancient folk knowledge has often tended to disappear in recent generations. Some authors hypothesize that even a quote in the Holy Bible may refer to Cynomorium
]. However, it is only recently that a few research groups [4
] have begun to look for confirmation of some of its traditional uses and to discover new biological activities.
An explanation for the lack of scientific knowledge we have of C. coccineum is that it grows in areas that are usually sparsely populated (deserts, rocky soils, salt marshes).
is present throughout almost the entire Mediterranean Basin, North Africa, and on the Arabic peninsula up to Western China. A second subspecies, C. coccineum
(Rupr.) J.Léonard, is present only in Asia, further east than C. coccineum
(including the Altay region, Inner Mongolia, Kazakhstan, Kirgizstan, Mongolia, Tadzhikistan, Turkmenistan, Uzbekistan, and the Xinjiang region) [8
]. The C. coccineum
is widely used in traditional Chinese medicine, and a large number of products containing this herb are marketed [9
]. Despite such a widespread use, only one review has been published on this subspecies [9
], whereas there has not been any summarizing article about C. coccineum
. This review aims to fill this gap by providing an overview of what is known about the chemical content and biological activity of C. coccineum
2. Botany and Folk Medicine
Multiple articles have been published about the taxonomic status and the phylogenetic placement of C. coccineum
and C. coccineum
]. For the sake of clarity and to be consistent with the recent phytochemical literature on Cynomorium
, in the present review, C. coccineum
will be referred to as C. coccineum
, and C. coccineum
as C. songaricum
is a holoparasitic plant, meaning that it does not perform photosynthesis and completely lacks chlorophyll, and therefore it is totally dependent on its host to obtain nutrients. This suggests a different metabolism and metabolic profile from photosynthetic plants, further increasing the scientific interest in this plant and other holoparasites. C. coccineum
is an herbaceous plant presenting an approximately 4–10 cm high, intensely red-brown inflorescence during the flowering period (Figure 1
), which is the only time when this species is visible above ground. It grows in sandy and rocky soils, usually in desert or subdesert habitats, forming haustorial connections with several plants, including Amaranthaceae (such as Atriplex
), Asteraceae, Cistaceae, Fabaceae, Frankeniaceae, Plumbaginaceae (Limonium
), and Tamaricaceae (Tamarix
The stem is covered by scale-like, reddish leaves that do not bear stomata. These scales become scarce towards the inflorescence, which itself comprises hundreds of reddish staminate, carpellate, and, in a lower number, bisexual flowers. C. coccineum is, therefore, most often monoecious. The staminate flower is made of (1–3) 4–6 (7–8) spatulate perianth parts forming a whorl or irregularly spiral arranged below a single stamen. The stamen filament nests in a longitudinal groove on the inner side of a semi-cylindrical or wedge-shaped pistillode with a truncated or notched apex. The carpellate flower is mostly made of a carpel with an elongated, grooved style, and its perianth is reduced to 1–8 small, free papillae at the summit of the ovary or along its sides.
According to Léonard (1986) [12
], C. songaricum
has male tepals that can be as wide as 1.5 cm, and the pistillode accompanying the anther filament is white, while in C. coccineum
, male tepals are never wider than 0.8 cm and the pistillode accompanying the anther filament is reddish. The pollen of Cynomorium
is tricolporate [13
]. The red color of the scales and flowers is due to flavonoids (vide infra
]. The almost cylindrical shape of the plant, combined with the absence of green color and its sprouting directly from the ground without any clearly visible leaves or stem, resulted in it being confused with a mushroom for a long time. In fact, C. coccineum
is known under several vernacular names reflecting this confusion, including Fungus Typhoides
, Fungus coccineus
, and Fungus gozitanum
, and also Maltese mushroom. The appellation ‘Maltese’ comes from a Maltese growing site of the plant (known as the Fungus Rock) off the coast of Gozo (Maltese archipelago), where the Knights of the Malta Medieval Order protected and used C. coccineum
to cure the bleeding wounds of knights struck in battle, and dysentery, rather frequent at that time because of the precarious hygienic conditions. C. coccineum
is also known in Arab countries as Tharthut, Tarthoorth, or Zobb el Ard.
Ibn Sina (980–1037 CE), also known in the west as Avicenna, was a Persian Muslim polymath who is regarded as one of the most significant physicians of the Islamic Golden Age [15
]. Avicenna mentions ‘Maltese mushroom’ [Cynomorium] as part of an excretory ointment,’ which ‘relaxes the bowels and is useful in treating chronic diarrhea’ [16
]. For an exhaustive description of medical prescriptions over the centuries, see the admirable work of Lanfranco (1960) [17
]. The ancient uses of C. coccineum
in traditional medicine are reported in Table 1
The scientific name Cynomorium
reflects the resemblance of the plant to a dog’s penis (in ancient Greek, “cyno
”). Due to this particular shape, many traditional uses of the plant involve the reproductive system [19
], in accordance to the Signatura Rerum
. The Signatura Rerum
(Doctrine of Signature) is an ancient document, formulated for the most part by Paracelsus, that describes the phenomenon whereby a plant, or a part of it, serves to heal precisely the organ of the human body from which it takes the shape. For instance, if a plant has a red juice, it will be expected to ‘cure the blood,’ or the walnut, having a brain shape, will be used to cure pathologies. In a similar way, in some cultures, C. coccineum
, with its phallic appearance, is considered an aphrodisiac for males, and in others, for females [24
]. The plant is also believed to affect fertility, show anti-hemorrhoidal properties, and regulate menstrual disorders [19
]. These popular beliefs have led some researchers to study C. coccineum
properties in more detail with regard to its effects on the reproductive system.
Despite a long history in traditional medicine, the phytochemistry of C. coccineum
is still largely unknown and has been the subject of a very limited number of studies so far (summarized in Table 2
). More phytochemical data are available for C. songaricum
, from which over 40 different chemicals have been identified, including phenolics (i.e., flavonoids, phloroglucinol derivatives, phenylpropanoids), steroids, organic acids, terpenoids, and sugars [9
-glucoside was identified as the pigment component of an acidified hydroalcoholic extract from the red inflorescence of the plant collected in Spain [14
], as well as from water extracts obtained from Sardinian samples [7
], while Harraz et al. (1996) additionally identified a minor presence (8% of total anthocyanins) of cyanidin 3-O
These anthocyanins are confined to the red external layer of small flowers and are almost absent in the colorless stem and internal part of the plant. So far, no anthocyanins have been described for C. songaricum
]. In the Asian subspecies, in fact, other types of flavonoids (i.e., flavan-3-ols, flavanones, and flavones) have been detected. The similar color of the two species suggests that some colored chemicals remain to be identified in C. songaricum
In general, several studies have reported that spectrophotometrically quantified flavonoids account for a significant portion (about 25–50%) of the total phenolic content of the plant [7
]. Some of these could possibly be procyanidin oligomers, as suggested by Zucca and co-workers [7
], but the authors failed to identify the chemicals.
Recently, Jabli et al. (2018) highlighted the coloring power of these anthocyanins for textile materials, suggesting a possible use as textile dyes [29
]. This could be a remarkable use of C. coccineum
, taking into account all the environmental concerns regarding the chemical durability and toxicity of synthetic dyes [30
As a principal component, gallic acid has been identified in almost equal distribution between the flowers and the colorless internal part of the plant by means of HPLC [7
]. The same authors highlighted unidentified HPLC peaks showing similarities with gallic acid derivatives (possibly gallotannins). Gallic acid was quantified at around 4 mg·g−1
dry extract, and could explain some biological properties of C. coccineum
(see below). For example, gallic acid has been reported to possess wound healing properties [31
] and constipating properties. Similar properties have been reported for fruits of other plants; for example, Terminalia chebula
fruits, used as an herbal remedy for diarrhea in traditional Chinese medicine, also contain tannins, including gallic acid and related glycoside derivatives, as major components of the ethyl acetate fraction [32
The presence of tannins and flavonoids was also recently confirmed in samples from Saudi Arabia, using spectrophotometric and qualitative assays [5
]. However, even in this case, no chromatographic identification was attempted. Using the same approach, the presence of glycosides, anthraquinones, saponins, alkaloids, and terpenes has been highlighted in extracts with different polarities (n
-butanol, water, aqueous methanol, and hexane) [5
In a recent work, Ben Attia et al. (2018) compared the chemical compositions of C. coccineum
plants from Sardinia and Tunisia, describing a differential chemical profile, possibly due to the climatic conditions (more arid in the Tunisian desert, and temperate in the Mediterranean basin). The phenolics, in fact, were differently distributed among solvents at various polarities [33
]. Additionally, these authors used 1
H-NMR to identify several amino acids (including proline, glutamine, valine, threonine, alanine, and asparagine) and mono-, bi-, and tricarboxylic organic acids (i.e., acetate, formate, and several common intermediates of biochemical pathways such as citrate, fumarate, malate, malonate, and succinate) in Sardinian and Tunisian samples. Moreover, sugars (i.e., β-glucose, α-glucose, fructose, and sucrose), as well as the two quaternary ammonium salts choline and betaine, were quantified in the same study. It resulted that betaine was significantly more concentrated in the samples from Tunisia. A correlation between betaine accumulation and abiotic stress (i.e., the arid climate) has been suggested, since betaine is known to be involved in osmoregulation and osmoprotection, being associated with environmental stresses such as salinity and extreme temperature [35
In a series of papers, the lipid profile of Sardinian C. coccineum
Supercritical Fluid Extract (SFE) oil has been elucidated [34
], showing an almost 1:1:1 concentration of saturated fatty acids (SFA, mainly palmitic acid 16:0 and stearic acid 18:0), monounsaturated fatty acids (MUFA, mainly oleic acid 18:1 n-9), and polyunsaturated fatty acids (PUFA) [28
]. The same authors confirmed this pattern in a Tunisian sample [33
], suggesting a promising nutraceutical source of functional and beneficial compounds (for example, about 11% of the SFE oils was 18:3 n-3). However, different accessions (also from the same geographical area) showed a high variability not only in the total quantity, but also in the oil composition [28
], probably due to different annual weather fluctuations or small differences in the collection/extraction procedures. The composition of fatty acids seems to be quite similar to that of C. songaricum
], with palmitic and oleic acid being the quantitatively most represented.
The compatibility of C. coccineum
formulations with the human diet was shown by the ‘Nutritional Facts Label’ (reporting the quantity of the three macronutrients), which established that 100 g of dried whole plant contained around 45 g carbohydrates, 9 g proteins, and approximately 1 g fatty acids, while total dietary fiber accounted for about 28 g [28
]. These findings seem to explain the use of C. coccineum
as an emergency food in time of famine, of which a few examples can be found in the literature [39
4. Antioxidant Activity
Reactive oxygen species (ROS) are unavoidable oxidized sub-products of cellular aerobic metabolism [40
]. This results in a paradox where, while most complex organisms require O2
for their existence, at the same time, oxygen is a highly reactive molecule that damages them by producing ROS [41
]. In recent decades, oxidative stress has been implicated in several degenerative processes, diseases, and syndromes, including: carcinogenesis, mutagenesis, impairment of fertility, atherosclerosis and cardiovascular disease, acute and chronic inflammatory diseases, oxidative photodegradation of ocular tissues, central nervous system disorders, and a wide range of age-related disorders (see Reference [41
] and references therein). Free radicals can also originate from prolonged exposure to UV light, cigarette smoke, and air pollution [42
Living organisms counteract the activity of free radicals through endogenous, enzyme-based antioxidant mechanisms (e.g., enzymes such as SOD and catalase) or mechanisms involving low molecular weight compounds (such as reduced glutathione) [43
]. Although the protective role of these molecules is very important, they are not completely effective in counteracting oxidative stress damage, and the introduction through the diet of exogenous antioxidant substances (vitamins, carotenoids, polyphenols, and anthocyanins) is strongly advised [44
]. Currently, great attention is being focused on the possible protective value of a wide variety of plant-derived antioxidant compounds, particularly those from fruits and vegetables. In plants, antioxidant molecules are produced as secondary metabolites and play a protective role against stressful conditions. The main classes of these compounds are phenolic acids, flavonoids, flavanols, and anthocyanins [46
]. The many beneficial effects on human health attributed to these compounds have given rise to a growing interest in the search for plant species with high antioxidant content and relevant biological activities (such as antimicrobial, anti-inflammatory, and anti-melanogenic activities).
Comparing antioxidant power is quite difficult, even inside a single plant species, as there is no uniformity in the use of extraction techniques, in the collection, conservation, and treatment methods of the raw material, or in the choice of the antioxidant assays used. Therefore, in this section we have tried to make a comparison and discuss the experimental data and the most widely used methods [47
] reported by different authors (and summarized in Table 3
These methods (transfer of electrons or hydrogen atoms, and determination of flavonoids and phenolics) generally provide a total estimate of the antioxidant power of a sample. Rached et al. (2010) related the total antioxidant power to the number of potentially antioxidant phytochemical compounds in aqueous and ethanol extracts of C. coccineum
grown in Algeria by means of an antioxidant activity test by TLC bioautography. This test gave several anti-radical spots [27
The authors compared the antioxidant power of C. coccineum
extracts with extracts from 52 different Algerian plants. Examination of Table 3
shows that C. coccineum
extracts had excellent antioxidant characteristics. The ethanol extract, in particular, possessed one of the highest contents in total phenols and flavonoids, and a value of [DPPH•] radical scavenging activity comparable to that possessed by BHT (butylated hydroxytoluene) a synthetic antioxidant widely used in the agri-food industry. Such a value was in line with that reported for a butanol extract of C. coccineum
collected in Saudi Arabia. In fact, Al-humaidi (2016) showed an IC50
value of 5.6 μg·mL−1
: a value very close to that of the ascorbic acid used as a control (Table 3
]. In this work, after removing the lipid material by treatment of dried C. coccineum
specimens with petroleum ether, a first extraction with methanol (raw extract) was performed, followed by other extraction phases with different extracting phases (aqueous methanol, butanol, water, and hexane). This double and sequential extraction procedure probably explains why the water extract of this study did not contain flavonoids, unlike what was reported in the work of Rached (2010). The 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) assay gave similar results for the various types of extract. The estimated IC50
] radical scavenging activity was maximal for the butanol extract, with values very close to those measured for ascorbic acid and the tocopherol used as a control.
Specimens of C. coccineum
grown and harvested in Sardinia (Arborea, Italy) showed a slightly lower antioxidant power for the whole plant (Table 3
). The authors of this study [7
], however, measured the antioxidant properties of the methanolic extract of C. coccineum
using different biochemical assays. They showed that this extract (5 µg) was able to inhibit the degradation of cholesterol in oxysterol by 70% in an in vitro model system. The protective antioxidant effect of the methanol extract was also exerted against Cu2+
-mediated degradation of liposomal unsaturated fatty acids in vitro.
A confirmation of the fact that the location and environmental conditions of plant growth can also affect the plants’ antioxidant power comes from a recent study. In the same laboratory, the same methods of extraction and analysis of C. coccineum
specimens grown and collected in geographically distinct places (Italy and Tunisia) with very different climatic characteristics [33
] were used. The C. coccineum
specimens were collected in a desert region in south-eastern Tunisia and in an area near the coast of Sardinia. These samples were macerated in sequence with increasing polarity solvents (n-hexane, chloroform, ethyl acetate, acetone, methanol, and water). The residual material coming from the maceration with the first solvent constituted the material that was extracted with the subsequent solvent. The peculiar extraction procedure described does not allow a comparison with the results reported in Table 3
, however, it allows some considerations. The five extracts thus obtained showed profound differences in terms of antioxidant properties. The differences depended on the type of extracting solvent. The highest antioxidant activity was retrieved in both acetone extracts, which also were the richest in polyphenols.
The specimens collected in the arid climatic zone were richer in anthocyanins, while the samples from Sardinia showed a higher content of total phenolics. The greater presence of anthocyanins in the Tunisian samples (arid climate) confirmed the role that these compounds play in drought stress. Overall, total antioxidant activity did not seem to be too different between the two samples, despite markedly different phenolic profiles.
The results shown above demonstrate that C. coccineum
extracts have a remarkable antioxidant activity, as shown by the comparisons with the antioxidant activity of ascorbic acid, alpha-tocopherol, and BHT. In some cases, substantial differences have been reported in relation to the extraction methods and solvents used. It is known that the process of extracting antioxidant molecules from plant material is influenced by various factors, such as quantity, chemical nature, extraction methods, the presence of interfering substances, etc. [48
]. Therefore, the extraction of antioxidant compounds from plant materials generally requires a set of different steps to ensure the removal of unwanted substances. In the case of C. coccineum
, extractions with polar organic solvents (MetOH, EtOH, and ButOH) are those that provide a greater yield. However, water extracts showed significant antioxidant power, which, combined with the other biological activities described below, opens the way to food applications for C. coccineum
Unfortunately, to our knowledge, no in vivo studies to date have confirmed the ability of this plant to counteract oxidative stress. This is a great lack, hindering the extension of the potential applications of C. coccineum-based formulations.
Until now, studies providing an overview of C. coccineum have mostly emphasized its historical background without reviewing its chemical content and biological activities. In this work, we have drawn attention to this plant that, although known for many centuries, has been partly ignored by current phyto- and folk medicine. Ancient European and especially Arab medicine took C. coccineum into great consideration for the preparation of remedies against bleeding, diarrhea and dysentery, and disorders of the reproductive system.
As far as we know, this is the first review on C. coccineum that has taken stock of the information provided by the few scientific studies conducted on this plant in the last forty years, that is, since the interest in this plant began to be addressed with the modern tools of scientific investigation. These studies indicate many biological activities of C. coccineum, some already reported by traditional medicine, and some completely new. In summary, C. coccineum seems to possess antioxidant power, antitumoral activity, and effects on the reproductive and cardiovascular systems. Unfortunately, almost all the studies have been conducted in vitro, and only marginal in vivo confirmation has been done. In particular, antitumoral activity seems to be the most promising. By contrast, although very attractive, data about the plant’s effect on the cardiovascular system are still too limited. These facts, combined with its action against tyrosinase, suggest that it could be a good candidate for nutraceutical applications or as an additive in the food industry. Its antimicrobial activity, on the other hand, could open the way to cosmetic applications.
The effect on reproductive systems could also be very promising from a commercial perspective, but comparison with current drugs is still needed. Additionally, the exact chemical(s) responsible for this activity have still not been identified. This step could allow an understanding of whether the effect is topical or extends to central nervous system. In particular, this issue is still unresolved for the C. songaricum-based commercial preparations.
Only a few compounds have been identified in the plant so far, so further in-depth studies are needed to shed light on a plant for which the uses date back centuries, but which has not yet revealed all its potential. An extensive phytochemical characterization of the plant extracts seems to be a mandatory step, combined with deeper in vivo assays of their ability to counteract oxidative stress. While new ways of exploiting the medicinal properties of C. coccineum are being developed, it will become necessary to ensure that both subspecies can be protected from extinction, either by regulating their collection in the wild or by cultivating them, so that they can be used sustainably.