Herbs in History: Marrubium

Marrubium Marrubium vulgare L. CONTENTS A Textbook Case Classical Identifications Summing Up Beyond Botany Back to Illustrations Conclusion References

By Alain Touwaide & Emanuela Appetiti | August 2023

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A Textbook Case

Horehound, White horehound, or Hoarhound (Marrubium vulgare L.) is a classic of medicinal plants therapy. It is widely used and is recognized to be specifically efficacious in treating coughs, colds, and congestion. On this basis, one would expect to easily trace it in the ancient literature and to possibly discover on this basis leads for possible renewed uses. The endeavour quickly appears to be more difficult than expected, however.
 

Classical Identifications

Reference material is not missing to establish a correspondence between ancient literature and modern taxonomy. Soon after Linnaeus (1707-1778) published his Systema Naturae in two volumes in 1758-1759, botanists scrutinized the ancient Greek texts on medicinal plants to identify their many species according to the new taxonomical system. One such botanist was John Sibthorp (1758-1796). Appointed Sherardian Professor of Botany at Oxford University in 1784 at age 26, he soon left England for Greece to do fieldwork. He personally examined and identified a great many species and had them reproduced by the botanical illustrator Ferdinand Bauer (1760-1826). Unfortunately, he could not publish the material he collected, which was edited and published posthumously in two works: first a Prodromus (Introduction) in two volumes (1806 and 1813), and then the Flora Graeca Sibthorpiana, published between 1806 and 1840 in ten large, lavishly illustrated volumes thanks to the  two botanists John Eward Smith (1759-1828) and John Lindley (1799-1855). Sibthorp was shortly followed in his endeavour by another Oxford scientist, Charles Daubeny (1795-1856), who did not work in the field, however, but studied ancient texts and the representations of the plants in the manuscript copies of these texts, as did also the German physician and historian of botany Kurt Sprengel (1766-1833) and, slightly later, the French botanist Edmond Bonnet (1848-1922).
 

Illustration 1: John Sibthorp, Flora Graeca Sibthorpiana, vol. 6 (1628), table 562: Marrubium pseudodictamnus. Reproduced from the Biodiversity Heritage Library.

Further on, research was performed by academics coming from such fields as botany, pharmacognosy, and philology. Among the botanists, there were Arthur Hort (1964-1935), who published a critical edition with English translation of Theophrastus, Historia Plantarum (Research on Plants), and the Spaniard Pio Font Quer (1888-1964), author of a massive treatise on medicinal plants entitled Dioscoride Renovado (Dioscorides Renewed); among the pharmacognosts, the Swiss August Tschirch (1856-1939), who compiled a multi-volume encyclopedia of the discipline, as well as his Greek colleague Emmanuel Emmanuel (1886-1972), who examined illustrations in manuscripts, and the German pharmacist Julius Berendes, author of a German translation of Dioscorides, De materia medica; and, among the philologists, the French Emile Littré (1801-1881), editor of the Greek text of the treatises attributed to Hippocrates that he also translated into French; and, more recently, the French classicist Suzanne Amigues (1937-2022), who re-edited Theophrastus’ Greek text with a translation.
 

Summing Up

Several of these erudite scientists and scholars have identified Marrubium in the ancient literature, including with species. Several Marrubium species were proposed for different ancient Greek names of plants.
 

Illustration 2a: Marrubium vulgare L. Specimen 21296 of the Herbarium collection of the Goulandris Natural History Museum, Athens, Greece, reproduced with permission.		Illustration 2b: Marrubium vulgare L. Photo from Royal Botanic Gardens Kew, Plant

All these identifications can be summarized as follows with the Greek name of the plants to which they correspond, which will be clarified further on in this article (between parentheses we indicate the source of the identification [author’s name and date of publication]):
 

• Marrubium spp. has been proposed for two Greek plant names:

  • prasion (Hort 1916)

  • pseudodiktamnos (Sibthorp, Flora 6 [1828]) (Illustration 1)
     

• Illustration 3a: Marrubium peregrinum L. Specimen 21384 of the Herbarium collection of the Goulandris Natural History Museum, Athens, Greece, reproduced with permission.		Illustration 3b: Marrubium peregrinum L.

  M. vulgare (Illustrations 2a and b) also corresponding to two different Greek names:

  • prasion (from Sibthorp Prodromus 1 [1806] to Fontquer 1982)

  • ēduosmon agrion (Emmanuel 1912)
     

• M. acetabulosum for diktamnos apo Kretes (from Crete) (Sibthorp, Prodromus 1 [1806], and Berendes 1902)
   

• M. catariaefolium about prasion (Berendes 1902; Bonnet 1903; Emmanuel 1912)
   

• M. creticum also about prasion (Sprengel 1807-1808)
   

• M. peregrinum about prasion (Illustrations 3a and b) (Sprengel 1807-1808 and 1829; and Amigues about Theophrastus)
   

• M. pseudodictamnum for different ancient plants:

  • gnafalion (Sibthorp, Flora 6 [1828])

  • diktamnos (Sprengel 1807-1808)

  • diktamnos eteros (other diktamnos) (Berendes 1902)

  • Illustration 4: prasion in manuscript New York, Pierpont Morgan Library, M 652, f. 131 recto, 2nd illustration, 10th century, Constantinople. Reproduced from the website of the library.		Illustration 5: diktamnos en Krētē in manuscript New York, Pierpont Morgan Library, M 652, f. 41 recto, 10th century, Constantinople. Reproduced from the website of the library.

    pseudodiktamnos (Sprengel 1807-1808; Daubeny 1857)
     

The plants of interest are thus the following with their ancient Greek names and their identifications above:
 

• prasion (Illustration 4)

  • Marrubium spp.

  • M. vulgare

  • M. catariaefolium

  • M. creticum

  • M. peregrinum
     

• diktamnos

  • M. pseudodictamnum
     

• diktamnos eteros (other diktamnos)

  • M. pseudodictamnus
     

• Illustration 6: pseudodiktamnon in manuscript New York, Pierpont Morgan Library, M 652, f. 198 verso, 10th century, Constantinople. Reproduced from the website of the library.		Illustration 7: ēduosmon agrion in manuscript New York, Pierpont Morgan Library, M 652, f. 58 verso, 1st illustraiton, 10th century, Constantinople. Reproduced from the website of the library.

  diktamnos apo Krētēs (from Crete) (Illustration 5)

  • M. acetabulosum
     

• pseudodiktamnos (Illustration 6)

  • Marrubium spp.

  • M. pseudodictamnon
     

• ēduosmon (Illustration 7)

  • M. vulgare
     

• gnafalion (Illustration 8)

  • M. pseudodictamnum
    
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A review of current taxonomy confirms several of the binomial designations above and indicates that some, instead, are now synonymous. The following designations are currently accepted names:

 

• Illustration 8: gnafalion in manuscript New York, Pierpont Morgan Library, M 652, f. 33 recto, 10th century, Constantinople. Reproduced from the website of the library.

  Marrubium (Lamiaceae)

  • M. vulgare L.

  • M. catariifolium Desr.

  • M. peregrinum L. (syn. M. Creticum Mill.
     

For each of Marrubium acetabulosum L. and M. pseudodictamnus two synonymies are present in current online literature (Plants of the World Online = POWO, and World Flora Online = WFO):
 

• M. acetabulosum:

  • Pseudodictamnus acetabulosus (L.) Salmaki & Siadati (POWO)
    (Illustration 9)

  • Ballota acetabulosa Benth. (WFO) (Illustrations 10a and b)
     

• M. pseudodictamnus:

  • Pseudodictamnus mediterraneus Salmaki & Siadati (POWO)
    (Illustration 11)

  • Ballota pseudodictamnus Benth. (WFO) (Illustration 12)
     

Illustration 9: Pseudodictamnus acetabulosa (L.) Salmaki & Siadati. Photo from Royal Botanic Gardens Kew, Plants of the World Online.

A clarification of these identifications would be possible if we were dealing with modern botany, through the description of the several species. However, this is not the case with the ancient literature. We do not have a description, but only illustrations for diktamnos, diktamnos apo Krētēs (from Crete) (Illustration 5), pseudodiktamnos (Illustration 6),  ēduosmon (Illustration 7), and gnafalion (Illustration 8). The only available description in the most comprehensive work on materia medica from Antiquity that was preserved through the century, De materia medica by the Greek Dioscorides (1^st cent. A.D.) is that of prasion (3.105):
 

prasion ... it is a shrub that has many branches growing from a single root. It is somewhat hairy and white and it has quadrangular stems. The leaf is as big as the thumb, somewhat round, thick, somewhat wrinkled, and bitter in taste. Spaced on the stem at intervals are the seeds and flowers, as if they were vertebrae. They are rough. It grows around building lots and ruins.

 
Apparently detailed, this description is not significant enough to allow for a clear determination.
 

Illustration 10a: Ballota acetabulosa (L.) Bentham Specimen 18072 of the Herbarium collection of the Goulandris Natural History Museum, Athens, Greece, reproduced with permission.		Illustration 10b: Ballota acetabulosa (L.) Bentham. Photo from Royal Botanic Gardens Kew, Plants of the World Online.		Illustration 11: Pseudodictamnus mediterraneus Salmaki & Siadati. Photo from Royal Botanic Gardens Kew, Plants of the World Online.		Illustration 12: Ballota pseudodictamnus (L.) Bentham. Specimen 20768 of the Herbarium collection of the Goulandris Natural History Museum, Athens, Greece, reproduced with permission.

 

Beyond Botany

Whereas the problem seems to be difficult if not impossible to solve, therapeutic indications help. For prasion, indeed, they are the following in Dioscorides, De materia medica (3.105):
 

Its dry leaves are boiled in water with its seed or are converted into juice when green, and the liquid is given with honey to phthisic and asthmatics patients, and to people who cough. It brings up congestive matter from the chest when mixed with dry iris.
 
It is given ... to people bitten by wild animals ...
 
... The leaves, plastered with honey, cleanse filthy sores, remove ... spreading ulcers ...
 
Also their juice, made by squeezing the leaves and condensing the liquid in the sun, is good for the same purposes.

 
We recognize here typical indications of Marrubium vulgare L. as in current literature, and we agree with earlier pharmaco-botanists in their identification of prasion as M. vulgare L.

This identification also provides a key to understand how plants with other ancient Greek names might have been identified as species of Marrubium or other genera in the Post-Linnean literature. Already in Dioscorides’ time, indeed, prasion = Marrubium was compared or even confused with other plants with which it presents some morphological, superficial similarity to a non-expert eye. Among these plants, there were the following:
 

• Origanum dictamnus L. (Dittany) (Illustration 13) and Dictamnus albus L. (Dittany) corresponding to diktamnos, diktamnos eteros and diktamnos ek Krētēs (from Crete);
   

• Mentha, esp. M. pulegium L.(Pennyroyal) (Illustration 14), corresponding to ēduosmon;
   

• Achillea maritima (L.) Ehrend. & Y.P.Guo (Cottonweed) (Illustration 15), corresponding to gnafalion;
   

• Ballota nigra subsp. foetida (Vis.) Hayek (syn. Marrubium ballota E.H.L. Krause) (Black horehound) (Illustration 16) corresponding to ballōtē not discussed above, but close to prasion = Marrubium in Dioscorides.
   

Illustration 13: Origanum dictamnus L. Photo from Royal Botanic Gardens Kew, Plants of the World Online.		Illustration 14: Mentha pulegium L. Photo from Royal Botanic Gardens Kew, Plants of the World Online.		Illustration 15: Achillea maritima (L.) Ehrend. & Y.P.Guo. Photo from Royal Botanic Gardens Kew, Plants of the World Online.		Illustration 16: Ballota nigra L. Photo from Royal Botanic Gardens Kew, Plants of the World Online.

Back to Illustrations

Arrived at this point of the inquiry, we should return to the illustrations identified by Post-Linnean scientists as representing species of Marrubium. We will not doubtthe validity of these identifications as most of their authors were authoritative pharmacognosts with a robust botanical education, particularly those of the 19^th century and early 20^th. Interestingly, two of the plants that have been recognized in these illustrations are adulterant of Marrubium vulgare L.: Ballota nigra L. (Black Horehound), and Marrubium peregrinum L. (also called Black Horehound). These and the other adulterants not listed here are morphologically similar to M. vulgare and have been reported as adulterants.
 
Although Dioscorides does mentions adulterations and ways to detect them in De materia medica, we should not interpret the different identifications of the plant in the illustrations as referring to adulterations, but rather as variations in either space (use of local varieties) or time (changes from one epoch to another). In this view, the differences in the illustrations reflect the process of substitution, which is well attested in the ancient pharmacognostic literature, and a certain fluidity in the selection of the species or even of the genera.
 

Conclusion

At first glance, Horehound seemed to be a classical case in the tradition of knowledge about the properties and applications of plants, allowing for an easy identification in earlier, historical literature and, on this basis, for the possible (re)discovery of applications now obsolete that might have been re-examined for efficacy purposes and safety verification. This was not the case, particularly because the basis of any research of this type—correct identification of the botanical genera and species—was more problematic than expected. However, the inquiry as above has made it possible to identify Marrubium vulgare L. with some probability of exactness. Surprisingly, it is not on the basis of a botanical description or representations of the plant, but through a set of indications that exactly correspond to a use that might be the most typical one of Horehound. And the action behind these indications is perfectly expressed in the ancient text—De materia medica by Dioscorides—in a way that current manuals of phytotherapy might use:
 

... it brings up congestive matter from the chest ...

 
Research on Horehound (Marrubium vulgare L.) as above results in a textbook case that exemplifies the complexity of investigations in ancient texts and the necessity to approach available information (with all the material, not only texts, but also illustrations and earlier pharmacognostic literature) in combination, approaching them from all angles in a cross-disciplinary way.

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