Marchantia polymorpha as a Source of Biologically Active Compounds

Abstract

Marchantia polymorpha L., also known as common liverwort or umbrella liverwort, is a spore-forming plant belonging to the Marchantiaceae family. This thallose liverwort has gained importance as a model plant, mainly because of its global distribution and easy and rapid in vitro culturing. A review of the literature shows that the major compounds in this species are undoubtedly sesquiterpenoids and bisbibenzyls. Among the sesquiterpenoids, it is worth mentioning cuparenes, chamigranes, and thujopsanes. Compounds belonging to these classes were found in specimens from Japan, China, Poland, Germany, and India and could be the chemical markers of this liverwort species. The key secondary metabolite of M. polymorpha is a macrocyclic bisbibenzyl, marchantin A. Marchantin-type aromatic compounds, together with other bisbibenzyls, such as riccardin D, isoriccardin C, or perrottetin E, demonstrated antifungal and antibacterial properties in various studies. In this review, we summarize the current knowledge on the diversity of compounds produced by M. polymorpha, emphasizing chemical variability depending on the origin of the plant material. Moreover, the biological activity of extracts obtained from this liverwort species, as well as single secondary metabolites, are described.

1. Introduction

Bryophytes are terrestrial, spore-bearing plants that comprise three phyla: liverworts (Marchantiophyta), mosses (Bryophyta), and hornworts (Anthocerophyta). These small nonvascular plants, phylogenetically placed between algae and ferns, are considered the first inhabitants of terrestrial habitats [1]. As the first land plants, they had to cope with adverse environmental conditions; hence, their ability to synthesize many different specialized secondary metabolites is extremely high. Indeed, such ‘chemical weapons’ are necessary for these small plants, since they the lack mechanical protection of higher vascular plants [2]. Among the bryophytes, the chemical constituents of the Marchantiophyta and their biological activity have been studied in great detail. Over the last 40 years, more than 3000 compounds have been found in this group of plants. Many of these products are characterized by unprecedented structures, and some, including the pinguisane-type sesquiterpenoids and the sacculatane-type diterpenoids, have not been found in any other plants, fungi, or marine organisms. This unique chemical composition increases the number of potential applications in medicine and beyond. In fact, the available literature data indicate that liverwort secondary metabolites show antibacterial, antifungal, cytotoxic, insect repellant, enzyme inhibitory, and proapoptotic activities [3,4,5].

Marchantia polymorpha L., also known as common liverwort or umbrella liverwort and belonging to the Marchantiaceae family (Figure 1), is the most widely distributed liverwort in the world. It is a cosmopolitan species that occurs from tropical to arctic regions [6,7].

This liverwort species has become one of the most important models for plant biology research and evolutionary genomics due to its relatively simple genome, global distribution, easy in vitro culturing, and unique phylogenetic position as a member of the early land plants [8,9]. As an evolutionary model, M. polymorpha contributes to our understanding of the evolution of plant defensive responses and the associated hormonal signaling pathways [9]. At this point, the following questions arise about the biologically active compounds present in this model plant: What do we know about them? Does Marchantia have its own characteristic metabolites? And are they used in medicine, horticulture, or for other purposes?

The aim of this paper is to review the available scientific literature concerning both the chemical composition and the biological properties of the most well-known liverwort species, M. polymorpha. Special attention was paid to the variability of the chemical composition depending on the origin of the plant material.

2. Chemical Diversity of M. polymorpha

Liverworts (Marchantiophyta) are plants that produce a wide array of biologically active secondary metabolites. These compounds are accumulated in the oil bodies, which are prominent and highly distinctive organelles uniquely found in liverworts [10]. Oil bodies are present in 95% of all liverwort species and are intracellular organelles bounded by a single unit membrane originating from dilated endoplasmic reticulum cisternae, containing lipophilic globules [11]. In the thallose liverworts like M. polymorpha, oil bodies are confined to scattered idioblastic oil body cells, while oil bodies of leafy liverworts are generally present in all cells [12]. The number, size, and colour of oil bodies are species specific. Oil bodies are estimated to serve a protective role for the plant, with their contents postulated to protect the plant against various biotic and abiotic stressors [13].

A review of the literature on the chemical composition of the umbrella liverwort shows that it is characterized by great diversity. The following groups of chemical compounds have been identified so far in Marchantia: monoterpenoids, sesquiterpenoids, and diterpenoids; sterols and triterpenoids; and bibenzyls, bisbibenzyls, phenanthrene derivatives, flavonoids, lipids, and other compounds (

Table 1. Secondary metabolites found in Marchantia polymorpha.

No.	Compounds	Formula	Geographic Origin	References
MONOTERPENOIDS
1	Limonene	C10H16	USA *	[14]
SESQUITERPENOIDS
acoranes
2	β-Acoradiene	C15H24	Poland	[15]
3	α-Neocallitropsene	C15H26	Poland	[15]
4	β-Alaskene	C15H24	Poland	[15]
5	Acorenone B	C15H24O	Poland	[15]
aromadendranes
6	α-Gurjunene	C15H24	Serbia, Turkey, USA *	[14,16,17]
7	Aromadendrene	C15H24	Turkey	[16]
8	Viridiflorol	C15H26O	Serbia	[17]
barbatenes
9	α-Barbatene	C15H24	Japan	[18]
10	β-Barbatene	C15H24	Japan, Turkey	[16,18,19,20]
bisabolanes
11	β-Bisabolene	C15H24	Japan	[19]
caryophyllanes
12	β-Caryophyllene	C15H24	Japan	[19]
cedranes
13	α-Cedrene	C15H24	Japan	[19]
14	7-epi-α-Cedrene	C15H24	Poland	[15]
15	β-Cedrene	C15H24	France	[21]
chamigranes
16	α-Chamigrene	C15H24	Japan, Germany, India	[20,22,23]
17	β-Chamigrene	C15H24	Germany, India, Poland, Japan, France, Serbia, USA *	[14,15,17,19,22,23,24,25]
18	ent-9-oxo-α-Chamigrene (Laurencenone C)	C15H22O	Japan, Germany, Poland	[20,22,24]
cuparanes
19	Cuparene	C15H24	Japan, Poland, France, Serbia, USA *	[14,15,17,18,19,25]
20	α-Cuprenene	C15H24	Japan, France, Poland	[15,19,20]
21	β-Cuprenene	C15H24	Japan, France	[19]
22	γ-Cuprenene	C15H24	Japan	[20]
23	δ-Cuprenene	C15H24	Japan, France, Poland	[15,19,20]
24	β-Microbiotene	C15H24	Poland	[15]
25	2-Cuparenol (=Cuparophenol, δ-Cuparenol, 2-Hydroxycuparene)	C15H22O	South Africa, Japan, France	[18,19,24,26]
26	ent-Cuprenenol	C15H26O	Japan, France	[19]
27	Cyclopropanecuparenol	C15H26O	Japan, France, Poland, Serbia	[15,17,19,20]
28	epi-Cyclopropanecuparenol	C15H26O	Japan, France, Poland	[15,19]
cyclomyltaylanes
29	Cyclomyltaylenol	C15H26O	Serbia	[17]
elemanes and bicycloelemanes
30	β-Elemene	C15H24	Japan	[19,21]
31	δ-Elemene	C15H24	Japan	[19,24,25]
32	Bicycloelemene	C15H24	Japan, France	[19]
eudesmanes
33	α-Selinene	C15H24	Turkey, Poland, Serbia	[15,17,19]
34	ent-β-Selinene	C15H24	India, Japan	[19,23]
35	α-Eudesmol	C15H26O	Turkey	[16]
36	β-Eudesmol	C15H26O	Turkey	[16]
eremophilanes
37	Eremophilene	C15H24	France	[21]
38	1(10),11-Eremophiladien-9β-ol	C15H24O	Germany	[27]
germacranes
39	Costunolide	C15H20O2	Japan	[28]
guaianes
40	5-Guaia-11-ol	C15H26O	Serbia	[17]
herbertanes
41	β-Herbertenol	C15H22O	Japan, Poland	[15,18,19]
42	ent-α-Herbertenol	C15H22O	Germany	[22]
himachalanes
43	α-Himachalene	C15H24	USA *	[14,25]
monocyclofarnesanes
44	(2Z,4E)-Abscisic acid	C15H20O3	USA	[29]
45	(2E,4E)-Abscisic acid	C15H20O3	USA	[29]
thujopsanes
46	ent-Thujopsene	C15H24	Japan, Poland, France, Serbia, USA *	[14,15,17,18,19,20,30]
47	ent-Thujopsan-7β-ol	C15H26O	Japan, Germany	[20,22]
48	ent-Thujopsenone (=Thujops-3-en-5-one)	C15H22O	Japan, France, Serbia	[17,18,19,20]
widdranes
49	Widdrol	C15H26O	Japan	[18,19]
DITERPENOIDS
50	Marchanol	C20H32O2	Vietnam	[31]
51	Labda-7,13E-dien-15-ol	C20H34O	Japan	[19,30,32]
52	Vitexilactone	C22H34O4	Vietnam	[31]
53	Phytol	C20H40O	South Africa, Poland	[15,19,33]
STEROLS and TRITERPENOIDS
54	Campesterol	C28H48O	South Africa, Germany, Japan, India, Taiwan	[22,23,24,33,34]
55	Brassicasterol	C28H46O	Japan	[24]
56	Dihydrobrassicasterol	C28H48O	Taiwan	[34]
57	Stigmasterol	C29H48O	South Africa, Japan, Germany	[22,24,33]
58	Sitosterol	C29H50O	South Africa, Germany, Taiwan	[22,33,34]
59	Clionasterol (24β-ethyl)	C29H50O	Taiwan	[34]
60	12-Oleanene-3-one	C30H48O	Vietnam	[31]
61	Ursolic acid	C30H48O3	Vietnam	[31]
62	3,11-Dioxoursolic acid	C30H44O4	Vietnam	[31]
BIBENZYLS
63	Lunularin	C14H14O2	Germany, Vietnam, China)	[19,22,31,35]
64	Lunularic acid	C15H14O4	Japan *, Germany	[36,37,38]
65	Prelunularic acid	C15H16O5	Japan	[38,39]
66	2,5-Di-O-β-d-glucopyranosyl- 4′-hydroxybibenzyl	C26H34O13	China	[40]
67	2-[3-(Hydroxymethyl) phenoxy]-3-[2-(4-hydroxyphenyl) ethyl]phenol	C21H20O4	China	[41]
BISBIBENZYLS
68	Riccardin C (=plagiochin G)	C28H24O4	South Africa, India, Vietnam, China	[23,31,33,35]
69	Riccardin D (=plagiochin E)	C28H24O4	China	[42]
70	Riccardin G (=plagiochin E methyl ether)	C29H26O4	China *	[35]
71	Riccardin H	C31H28O4	China	[42]
72	Isoriccardin C	C28H24O4	India, Vietnam	[23,31]
73	Isoriccardin D	C28H24O4	China	[41]
74	13,13′-O-Isopropylidenericcardin D	C31H28O4	China	[42]
75	Polymorphatin A	C28H24O4	China	[41]
76	Marchantin A	C28H24O5	China, Germany, India, Japan, Serbia, Vietnam	[19,22,23,25,30,31,35,42,43,44,45,46]
77	7′,8′-Dehydromarchantin A	C28H24O4	Serbia *	[43]
78	Marchantin B	C28H24O6	China, Germany Japan	[19,22,30,35,42,43,45]
79	Marchantin C	C28H24O4	South Africa, Germany, India, Japan, Serbia *	[19,22,23,30,33,43,45]
80	Marchantin D	C28H24O6	Germany, India, China	[22,23,30,35,45,47]
81	Marchantin E	C29H26O6	China, Germany, India, France, Serbia *	[19,22,23,30,35,42,43,45]
82	Marchantin F	C28H24O7	South Africa, China	[35]
83	Marchantin G	C28H22O6	Japan	[47]
84	Marchantin H	C28H24O5	South Africa,	[33]
85	Marchantin J	C30H28O6	China, Germany	[22,41]
86	Marchantin K	C29H26O7	Germany, Vietnam, China	[22,31,35]
87	Marchantin L	C28H24O6	Germany	[22]
88	Isomarchantin C	C28H24O4	India	[23]
89	Neomarchantin A	C28H24O4	China	[42]
90	Perrottetin E	C28H26O4	China, India	[23,35,41]
OTHER AROMATICS
91	3R-(3,4-Dimethoxybenzyl)- 5,7-dimethoxyphthalide	C19H20O6	Vietnam	[31]
92	Marchatoside	C20H22O7	Vietnam	[31]
93	3-(3,4-Dihydroxyphenyl)- 8-hydroxyisocoumarin	C15H10O5	Germany *	[37]
94	2,3-Dimethoxy-7-hydroxy- phenanthrene	C16H14O3	Germany *	[37]
95	2,7-Dihydroxy-3-methoxy- phenanthrene	C15H12O3	Germany *	[37]
96	3,3′-Dimethoxy-2,2′,7,7′-tetra- hydroxy-1,1′-biphenanthrene	C30H22O6	Germany *	[37]
97	2-Hydroxy-3,7-dimethoxy phenanthrene	C16H14O3	India	[23]
98	m-Hydroxybenzaldehyde	C7H6O2	Germany	[22]
99	p-Hydroxybenzaldehyde	C7H6O2	South Africa, Germany	[22,33]
100	3-Methoxy-2,2′,3′,7,7′-pentahydroxy- 1,1′-biphenanthrene	C29H20O6	Germany *	[37]
101	2,2′,3,3′,7,7′-Hexahydroxy- 1,1′-biphenanthrene	C28H18O6	Germany *	[37]
102	2-(3,4-Dihydroxyphenyl)-ethyl- β-d-allopyranoside	C14H20O8	China	[40]
103	2-(3,4-Dihydroxyphenyl)-ethyl- β-d-glucopyranoside	C14H20O8	China, Germany *, Japan	[37,40,48]
104	2-(3,4-Dihydroxyphenyl)-ethyl- O-α-l-rhamnopyranosyl-(1→2)- β-d- allopyranoside	C20H30O12	China	[40]
105	2-(3,4-Dihydroxyphenyl)-ethyl- O-β-d-xylopyranosyl-(1→6)- O-β-d-allopyranoside	C19H28O12	China	[40]
106	Salidroside	C14H20O7	Japan	[48]
107	Indole acetic acid	C9H7O2N	USA	[29]
FLAVONOIDS
108	Apigenin	C15H10O5	Germany *, New Zealand	[37,49,50]
109	Apigenin-7-O-β-D-glucuronide	C21H18O11	New Zealand	[49,50]
110	Apigenin-7,4′-di-O-glucuronide	C27H26O17	New Zealand	[49,50]
111	Luteolin	C15H10O6	Germany	[22,49,50]
112	Luteolin-7-O-β-D-glucuronide	C21H18O12	New Zealand	[49,50]
113	Luteolin-7,3′-di-O-β-glucuronide	C27H26O18	New Zealand	[49,50]
114	Luteolin-7,4′-di-O-β-glucuronide	C27H26O18	New Zealand	[49,50]
115	Luteolin-3′4′-di-O-β-glucuronide	C27H26O18	New Zealand	[49,50]
116	Luteolin-3′-O-β-glucuronide	C21H18O12	New Zealand	[49,50]
117	Luteolin-7,3′4′-tri-O-β-glucuronide		New Zealand	[49,50]
118	Artemetin	C20H20O8	Vietnam	[31]
119	Kaempferol	C15H10O6	Vietnam	[31]
120	Quercetin	C15H10O7	Vietnam	[31]
121	Aureusidin-6-O-g1ucuronide	C21H18O12	New Zealand	[51]
122	5,3′,4′-Trihydroxyisoflavone- 7-O-β-d-glucopyranoside (=Orobol-7-O-glucoside)	C21H20O11	China	[40]
123	Riccionidin A	C15H9O6	Germany *	[52]
124	Riccionidin B	C30H17O12	Germany *	[52]
LIPIDS
125	Palmitic acid (16:0) (=Hexadecanoic acid)	C16H32O2	Japan *	[20,53]
126	Ethyl palmitate (=Hexadecanoic acid ethyl ester)	C18H36O2	Japan	[20]
127	Stearic acid (18:0) (=Octadecanoic acid)	C18H36O2	Japan *	[53]
128	Palmitoleic acid (16:1n-7) (=9-Hexadecenoic acid)	C16H30O2	Japan *	[53]
129	Oleic acid (18:1n-9) (=9-Octadecenoic acid)	C18H34O2	Japan *	[53]
130	Linoleic acid (18:2n-6) (=9,12-Octadecadienoic acid)	C18H32O2	Japan *	[20,53]
131	α-Linolenic acid (18:3n-3) (=9,12,15-Octadecatrienoic acid)	C18H30O2	Japan *	[53]
132	Arachidonic acid (20:4n-6) (=5,8,11,14-Eicosatetraenoic acid)	C20H32O2	Japan *	[53,54]
133	EPA (20:5n-3) (=5,8,11,14,17-Eicosapentaenoic acid)	C20H30O2	Japan *	[53,54]
134	Oxacycloheptadecan-2-one	C16H30O2	Japan	[20]
OTHER COMPOUNDS
135	Shikimic acid 4-(β-d-xylopyranoside)	C12H18O9	China	[40]

* axenic or cell culture.

).

Such a great chemical diversity of M. polymorpha, shown in Table 1, suggests the heterogeneity of this liverwort species. Marchantia is characterized by high morphological variability, which has led to the description of many synonymous “species” and subspecific taxa [8]. Based on the analysis of morphological characters, isozyme patterns, RFLP (nrDNA), RAPD markers, and ecological preferences, three subspecies of M. polymorpha are distinguished. These are M. polymorpha subsp. polymorpha, M. polymorpha subsp. montivagans, and M. polymorpha subsp. ruderalis. The available literature data indicate that the subsp. polymorpha corresponds to the plant previously known as Marchantia aquatica, while the subsp. montivagans corresponds to the liverwort known as Marchantia alpestris. Only the subsp. ruderalis corresponds to M. polymorpha (sensu stricto). These three taxa differ in habitat, although they sometimes occur sympatrically [55,56,57]. More detailed analyses conducted by Linde and his associates [58] revealed a more complex pattern, with evidence suggesting hybridization and introgression between subspecies.

When reviewing the literature on chemical composition, unfortunately, there is almost no data on the occurrence of plant metabolites in individual subspecies. Most of the publications refer simply to M. polymorpha without indicating the subspecies. The data included in Table 1 suggest that most of the metabolites were identified and/or isolated from subsp. ruderalis. This is also supported by the ecological preferences of individual subspecies. Boisselier-Dubayle and coworkers [55] showed that M. polymorpha subsp. polymorpha occurs chiefly in flooded habitats, and subsp. montivagans grows in wet habitats in the mountains, while subsp. ruderalis colonizes preferentially man-made habitats, implying that, when collecting plant material, it is easiest to encounter M. ruderalis.

The phytochemistry of M. polymorpha also varies depending on its place of origin. The major chemical compounds contributing to the phytochemical complexity of this liverwort species are distributed among two groups: sesquiterpenoids and bisbibenzyls. A comparison of the chemical composition of the available data concerning subspecies, as well as geographical distribution in relation to the most characteristic metabolites of M. polymorpha, are presented in

Table 2. Distribution of sesquiterpenoids and bisbibenzyls in relation to M. polymorpha subspecies and geographical origin.

Characteristic Compounds	Subspecies			Geographical Origin
	Mpr	Mpp	Mpm	Japan	Poland	Germany	France	Serbia	Turkey	India	China	Vietnam	South Africa	USA
SESQUITERPENOIDS
Acoranes	✓				✓
Aromadendranes		✓	✓					✓	✓					✓ *
Barbatanes				✓					✓
Bisabolanes				✓
Caryophyllanes				✓
Cedranes				✓	✓		✓
Chamigranes	✓			✓	✓	✓	✓	✓		✓				✓ *
Cuparanes	✓			✓	✓	✓	✓	✓					✓	✓ *
Cyclomyltaylanes		✓	✓					✓
Elemanes				✓			✓
Eudesmanes		✓	✓	✓				✓	✓	✓
Eremophillanes		✓				✓	✓
Germacranes				✓
Guaianes		✓	✓					✓
Herbertanes				✓	✓	✓
Himachalanes														✓ *
Monocyclofarnesanes														✓
Thujopsanes	✓			✓	✓	✓	✓	✓						✓ *
Widdranes				✓
BISBIBENZYLS
Marchantin A	✓			✓	✓	✓		✓		✓	✓	✓
Marchantin B				✓		✓					✓
Marchantin C	✓			✓		✓		✓ *		✓			✓
Marchantin D						✓				✓	✓
Marchantin E	✓					✓	✓	✓ *		✓	✓
Marchantin F											✓		✓
Marchantin G				✓
Marchantin H													✓
Marchantin J						✓					✓
Marchantin K						✓					✓	✓
Marchantin L						✓
Isomarchantin C										✓
Neomarchantin A											✓
Riccardin C										✓	✓	✓	✓
Riccardin D											✓
Riccardin G											✓ *
Riccardin H											✓
Isoriccardin C										✓		✓
Isoriccardin D											✓
Perrottetin E										✓	✓

* cell culture; Mpr—M. polymorpha subsp. ruderalis; Mpp—M. polymorpha subsp. polymorpha; Mpm—M. polymorpha subsp. montivagans.

.

2.1. Sesquiterpenoids

Marchantia polymorpha is a rich source of terpenoids, in particular those belonging to the sesquiterpene group. Forty-eight sesquiterpenoids belonging to twenty different classes are included in Table 1. The structures of selected sesquiterpenoids characteristic of M. polymorpha are presented in Figure 2.

The first sesquiterpenoid reported from M. polymorpha was (S)-2-hydroxycuparene (=2-cuparenol). Its isolation was conducted in 1974 by Hopkins and Perold [26] from a South African specimen. Two cuparane-type alcohols, cyclopropanecuparenol and its epimer, are the major volatile components of this species. Besides the mentioned alcohols, other cuparanes are present in M. polymorpha, namely cuparene and α-, β-, γ-, and δ-cuprenene. Thujopsanes and chamigranes are other sesquiterpenoids characteristic of M. polymorpha. They are represented by thujopsene, thujopsan-7β-ol, thujopsenone, α- and β-chamigrene, as well as ent-9-oxo-α-chamigrene [12,18]. The data included in Table 2 show that these sesquiterpenoids (cuparanes, chamigranes, and thujopsanes) could be chemical markers of M. polymorpha subsp. ruderalis. Occasionally, this subspecies can produce metabolites characteristic of a single specimen. In the Polish collection of M. polymorpha, acorane-type sesquiterpenoids were identified. The presence of α-neocallitropsene, acorenone B, β-alaskene, and β-acoradiene were confirmed [59,60].

Our recent preliminary data concerning volatile components present in the Serbian M. polymorpha subspecies showed that the subspecies polymorpha and montivagans are very different with reference to sesquiterpene composition. In the case of these subspecies, the presence of cuparane-, chamigrane-, and thujopsane-type compounds was not demonstrated, while compounds belonging to aromadendranes, guaianes, and eudesmanes were identified [17]. A very similar chemical composition was also observed in the sample from Turkey [16]. Although the authors did not specify the subspecies of the specimen studied, it can be inferred that it is not M. ruderalis.

2.2. Bibenzyls and Bisbibenzyls

Bibenzyls are organic compounds with a C6-C2-C6 skeleton, which are synthesized by the phenylpropanoid pathway, like polyphenols [61]. Common liverwort is reported to produce only a few compounds; among them, it is worth mentioning lunularin and lunularic acid [23,26,62]. Both metabolites are direct precursors in the biosynthesis of marchantin C, a bisbibenzyl, which is later transformed to form marchantin A [63].

Bisbibenzyls are macrocyclic compounds consisting of two bibenzyl units. Acyclic bisbibenzyl compounds are linked once, while the cyclic ones are linked twice. The most important bisbibenzyl found in M. polymorpha is marchantin A. It is derived from lunularic acid, with two ether linkages between C₁–C_2′ and between C₁₄–C_11′ (Figure 3). The majority of common liverwort specimens contain marchantin A in large amounts. In fact, it was reported to be present in common liverwort from various countries (Table 1). This, however, is not true for South African M. polymorpha, which, according to some studies, does not contain marchantin A at all [33]. Its place as the major cyclic bisbibenzyl is taken by marchantin H. Moreover, marchantin E has been isolated form Indian and French specimens [5]. Marchantin A is also commonly found in many other plants from the Marchantiales [64,65] and other Marchantiophyta [66].

Riccardins are another group of cyclic bisbibenzyl compounds present in M. polymorpha. Japanese and Indian specimens of M. polymorpha contain riccardin C [13,22,40]. Riccardin H, isoriccardin D, and 13,13′-O-isopropylidenericcardin D were found in M. polymorpha from China [62]. Isoriccardin C was found in Chinese, Indian, and Vietnamese plant material [13,62,67].

Other bisbibenzyls that can be found in common liverwort are perrottetin E and polymorphatin A. Perrottetin E is an acyclic bisbibenzyl found in Indian and Chinese specimens of common liverwort [13,62]. It can be used as a precursor for the synthesis of marchantin- and riccardin-type compounds [33]. Polymorphatin A is a cyclic compound linked with one ether C₁–C_2′ linkage and one biphenyl C₁₂–C_12′ linkage. This bisbibenzyl was first found in Chinese M. polymorpha [62]. Representatives of riccardins and other bisbibenzyls are presented in Figure 4.

Based on the data presented in Table 2, specimens from European countries and Japan are characterized by the occurrence of only marchantin A derivatives. On the other hand, those from India, China, and Vietnam, as well as South Africa, in addition to marchantin-type compounds, also produce those belonging to the riccardin and perrottetin types.

2.3. Other Compounds

Flavonoids are ubiquitous minor components in the Marchantiophyta, including M. polymorpha [3,4,68]. The main flavonoid types present in this species are flavone O-glucuronides. Luteolin, apigenin, and their derivatives are the most abundant, as shown in Table 1.

Another interesting biochemical feature of M. polymorpha is represented by two polyunsaturated fatty acids, arachidonic acid (ARA, 20:4n-6) and eicosapentenoic acid (EPA, 20:5n-3). Shinmen et al. [54] have reported that culture of M. polymorpha contained high amounts of ARA and EPA (92 and 48 mg L⁻¹, respectively) under photomixotrophic conditions.

Among other products of M. polymorpha, it is worth mentioning monoterpenoids and diterpenoids, sterols and triterpenoids, phenanthrenes, phthalides, and other aromatic compounds. Characteristic diterpenoids can be found in Vietnamese specimens, such as marchanol, belonging to the clerodane-type compounds, and vitexilactone from the labdane group [31].

Marchantia polymorpha does not synthesize monoterpenes, apart from limonene, which was reported at the initial stage of growth in cell culture [14].

The sterols and triterpenoids found in common liverwort are similar to those found in the higher plants. Among the sterols, the presence of sitosterol and stigmasterol was confirmed, while among triterpenoids, the occurrence of ursane- and oleanane-type compounds was reported [22,31,33]. Phenanthrene derivatives were found in the field collection of M. polymorpha from India [23], as well as from cell cultures in Germany [37]. Finally, the presence of two phthalides, 3R-(3,4-dimethoxybenzyl)-5,7-dimethoxyphthalide and marchatoside, was confirmed in a Vietnamese collection [31].

The chemical structures of selected diterpenoids and triterpenoids, flavonoids, phenanthrenes, and phthalides are presented in Figure 5.

3. Biological Activities

Common liverwort has a long history in ethnomedicine [64]. It was used as an antipyretic, antihepatic, antidotal, and a diuretic medicinal plant [69].

Extracts of M. polymorpha were repeatedly proven to possess antifungal properties [42,70,71,72,73]. Many fungi are susceptible to growth inhibition when subjected to these extracts, including Candida albicans [35,70,74], Cryptococcus neoformans, Tilletia indica, Fusarium oxysporum f.sp. lini, Sclerotium rolfsii, Rhizoctonia solani [42,71], Alternaria solani [74], Fusarium solani [73], and Trichophyton mentagrophytes [35,74]. Studies of activity against C. albicans determined that neomarchantin A, riccardin D, and 13,13′-O-isopropylidene-riccardin D are the most effective compounds, while marchantin A, B, and E and riccardin H, even if possessing some antifungal activity, were not as effective [70]. The activity also varies depending on the solvent used for extraction. Riccardin D (called by the authors plagiochin E), found in Chinese M. polymorpha, exhibits inhibitory properties against C. albicans, which were increased when combined with fluconazole. When examined in more detail, this compound was found to reverse the fungal resistance to the azole drug by inhibiting its efflux from C. albicans [75]. Transmission electron microscopy showed serious damage in the structure of the yeast cell wall after treatment with plagiochin E. Inhibition of chitin synthesis was detected, deriving from downregulation of the expression of CHS1 and upregulation of the expression of CHS2 and CHS3 [76]. Moreover, exposure to plagiochin E resulted in an elevation of the membrane potential and a decrease of the ATP level in mitochondria, which caused ROS accumulation [77]. This effect induced typical markers of apoptosis in the yeast cells, such as chromatin condensation, nuclear fragmentation, and G₂/M cell cycle arrest. The latter event was related to downregulation of cyclins (CDC28, CLB2 and CLB4), as well as metacaspase activation [78].

Antibacterial activity of extracts from M. polymorpha is also an important subject of studies on common liverwort, although no information has been collected so far with reference to the mechanisms of action. Besides the crude extracts [71,74], marchantin A also exhibits such properties; in fact, its inhibitory effect has been documented on both Gram-positive and Gram-negative bacteria, such as Acinetobacter calcoaceticus, Bacillus cereus, Bacillus megaterium, Bacillus subtilis, Escherichia coli, Haemophilus influenzae, Listeria monocytogenes, Neisseria meningitidis, Pasteurella multocida, Pseudomonas aeruginosa, Proteus mirabilis, Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pyogenes, and Streptococcus viridans [23,42,62,68,79,80]. Antibacterial effects have been also documented in the case of isoriccardin C [62]. Lines of M. polymorpha were also subjected to genetic engineering in order to obtain a mutant with a higher potential for the synthesis of antibacterial compounds [35].

In vitro studies have shown that organic extracts of M. polymorpha exhibit cytotoxic activity [81,82], deriving from their content in bioactive products. A more detailed study conducted in 2008 showed that marchantin A induces growth inhibition on the breast cancer cell lines A256, MCF-7, and T47D, based on an antimicrotubular effect which was increased when marchantin A and an Aurora-A kinase inhibitor were used simultaneously [83]. Marchantin A also demonstrated cytotoxicity against the malignant melanoma cell line A375 while having less cytotoxic activity against keratocytes and not affecting tyrosinase activity in a model assay [84]. Lunularin also exhibited potent cytotoxic activity against MCF-7 [62].

Marchantin A exhibits DNA polymerase β-inhibitory and anti-HIV activities [85]. Moreover, along with marchantins B and E, plagiochin A, and perrottetin F, it possesses anti-influenza activity deriving from its targeting of the PA subunit of endonuclease. These products have a 3,4-dihydroxyphenethyl group in common, which is indicative of the importance of this moiety for this kind of bioactivity [86]. Marchantin A was also found to inhibit the proliferation of the erythrocytic stages of two Plasmodium falciparum strains, as well as other protozoans, such as Trypanosoma brucei rhodesiense, T. cruzi, and Leishmania donovani [87]. Its antitrypanosomal activity was also documented by another research group, along with marchantin E [88]. However, marchantin A has a low sensitivity index towards the aforementioned parasites, so the therapeutic window is rather narrow [1].

While tested for its antioxidant properties, marchantin A showed free radical scavenging ability [35] depending on its concentration. It also ties in to the anti-inflammatory properties of M. polymorpha, originating in its ethnomedicinal uses. Marchantins A, B, D, and E, isoriccardin C, and perrotetin D demonstrated an inhibitory effect on 5-lipoxygenase and cyclooxygenase, key enzymes in the arachidonic acid cascade [89]. The strength of this effect is structure dependent, as marchantin D exhibited lower inhibition toward 5-lipoxygenase. Along with lunularin, isoriccardin C has also displayed strong DPPH radical scavenging activity [62].

A chloroform extract of M. polymorpha was postulated to have hepatoprotective properties [90]. When mice were administered with paracetamol in liver-damaging quantities along with marchantin A, the amount of markers of liver damage in mice blood (aspartate transaminase and alanine transaminase) was significantly lower than in the control group administered with paracetamol only, and on par with the group in which paracetamol was administered along with silymarin. Another study showed that flavonoids of M. polymorpha can protect liver cells from injuries caused by the administration of carbon tetrachloride [91]. As both compounds induce damage to liver cells with their oxidizing potential, the hepatoprotective effect was postulated to be due to the antioxidant properties of M. polymorpha extracts.

Marchantin A, riccardin A, marchantin B, and other compounds from M. polymorpha also have an inhibitory effect on lipopolysaccharide production induced by nitric oxide [92]. As nitric oxide is postulated to play a role in the etiology of chronic neurodegenerative diseases [93], this property should be more closely investigated in the future.

Structural similarity between cyclic bisbibenzyl compounds and bisbenzylisoquinoline alkaloids, such as tubocurarine, has led to the investigation of the muscle relaxation properties of marchantin-type compounds [94]. In a study published in 1995 [95], marchantin A was used in comparison to cepharanthine, a muscle relaxant. Both compounds expressed similar properties and were bound to a common receptor, which points to the muscle-relaxing properties of marchantin A likely being owed to the binding of calcium molecules. This may also tie in with the inhibition by marchantin A of calmodulin [95], a protein with activity related to calcium levels in the cell.

4. Conclusions and Future Perspectives

Although bryophytes are among the oldest land plants, their usefulness is relatively unknown to most people. There is very little knowledge available about the medicinal properties of bryophytes. An ancient method of determining the medicinal properties of plants was based on the concept of Paracelsus, dealing with the resemblance of plant body parts to the shape and structure of organs in the human or animal body for which it is remedial. As per the abovementioned philosophy, M. polymorpha was used to cure hepatic disorders [96]. This liverwort was also used as a medicine for boils and abscesses, perhaps because the young archegoniophore resembles a boil when it first emerges from the thallus [97].

From this perspective M. polymorpha became a very interesting case study. This liverwort is present in almost all environments and has a very versatile phytochemical profile, especially including bisbibenzyl compounds. These compounds are almost unique to liverworts, as their presence has so far only been confirmed for plants of the Primula genus [1,5]; they have disclosed particular interest in biological activity studies and may be the foundation of new plant medicines or plant protection products.

However, until now, no products derived from M. polymorpha are available on the market. Also, to the best of our knowledge, no clinical, pre-clinical or toxicological studies have been carried out so far. Although the exact mode of action of some of the described bioactive compounds remains unknown, M. polymorpha and its metabolites could serve as an attractive candidate for therapeutic properties. Further work on the isolation, characterization, structural elucidation, pharmacological evaluation, determination of mode of action, and clinical trial of these active principles could open exciting perspectives in future drug development programs.

The secondary metabolites of M. polymorpha endophytes show applicative potential as well. They exhibit selective cytotoxicity toward several cancer cell lines and antiviral properties [15,98], calling for more accurate investigations on their occurrence and bioactivities. As of late, our team is trying to establish the optimal ways to cultivate these bryendophytes and to extract and evaluate their products.

As we managed to summarize in this article, the therapeutic potential of M. polymorpha is yet to be fully explored, but, even now, it holds potential for many future studies, which may result in crucial findings.