POLYGONACEAE

The Polygonaceae are mostly wiry-stemmed herbaceous plants, shrubs and lianes of the temperate Northern Hemisphere but there are also a few trees native to the tropics and some grow naturally in the Southern Hemisphere. There are about 1150 species world wide.

The common feature in all members of this family is an ochrea—a peculiar membrane-like sheath which surrounds the stem above each swollen node where leaf stalks are attached. It is formed from modified stipules which in many other families are a pair of flaps at the leaf base.

Many species contain oxalic acid in their tissues which gives a sharp taste to some e.g. sorrel leaves, but is poisonous in others, e.g. rhubarb leaves.

Plants of economic importance include Fagopyron esculentum (buckwheat), Rumex acetosa (sorrel) and Rheum spp. (rhubarbs).

Rheum officinale

Chinese rhubarb

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Family Polygonaceae

In addition to R. officinale and R. palmatum, a third species of Chinese rhubarb, R. tanguticum, is also officially part of pharmacopoeial Rhizoma Rhei, called Dahuang in Chinese.

Description

R. officinale is a taller, larger perennial, more than 3 m in flower. Leaves grow on long reddish stems and are up to a 1 m across; ovate, with 5–7 shallow irregular lobes and prominent veins. Flowers white in large panicles, blooming in summer.

Odour—characteristic, aromatic; taste—slightly astringent and bitter.

Habitat and cultivation

R. officinale prefers a sunny situation and well drained but moist soils. It can be cultivated in countries with a similar cold climate and soils but does not do well in hot humid areas. It may be grown from seed or division of the roots.

Parts used

Roots and rhizomes harvested, preferably when they are at least 6 years old, in autumn or early spring.

Active constituents1–3

1) Hydroxyanthracenes

a) anthraquinones (about 3%),4 complex in nature, some free but present mostly as glycosides of emodin (about 2.6%), rhein, aloe-emodin, chrysophanol and physcion5–7

b) dianthrones including sennosides A and B7,8

2) Tannins (5–10%) including galloylglucosides, procyanidins and gallic acid9

3) Stilbenes including resveratrol10

4) Flavonoids including catechin

5) Phenylbutanones including lindleyin11,12

Also contains volatile oil including cinnamic acid.13

There is geographical variation amongst these Rheum species which also alters their chemical make-up2,14 and there are qualitative and quantitative differences between the species. R. officinale appears to have lower levels of the above active constituents3,15 whereas R. palmatum and R. tanguticum are quite similar. The different species are hard to identify based on their appearance and this is therefore done chemically. In practice the herb is likely to be a mixture of all three official species.2,15

Nutritional constituents

Vitamins: A, C and B complex

Minerals: Sodium, potassium, iron, sulphur and phosphorus

Actions

1) Laxative

2) Astringent

3) Tonic

4) Stomachic

5) Aperient

Scientific information

Rheum is a valued and long-established medicine in the East and has been an official preparation in many pharmacopoeias across the world.16 In the west it has been used mainly as a purgative16 but the range of uses is much broader in their countries of origin. There are a number of pharmacologically active constituents that have received scientific study although the hydroxyanthracenes are the main ones involved in purgation. A central action that may help give its broad ranging uses as seen in eastern medicine is the fact that it is a strong anti-oxidant17,18 and this is due to a number of its constituents.19–21

Cancer support

In vitro—The anthraquinones have potent antitumour properties for a variety of cancer cell lines including liver,22,23 multiple myeloma,24 leukaemia,25–27 oral,10,28 gastric,29 ovarian,30 prostate,31 epidermal,31 lung,32–37 pancreatic32 and breast.32,38 Their mechanisms as anticancer agents are multi-factorial and includes the induction of apoptosis and cell-cycle arrest,39 disruption of mitochondrial function,26 damage to DNA,10 protection against chemical mutagens40–42 and the inhibition of metastatic spread43–45 and angiogenesis.46 Tumor cells are more sensitive to these actions than normal cells.10,47 In addition the anthraquinones may enhance the activity of cancer chemotherapeutic agents.47 Stilbene constituents may have anticancer potential too.10 Rheum is one of the four main herbs contained in Essiac tea which has been widely used as part of complementary cancer treatment. Essiac is strongly anti-oxidant and protects DNA from free radical damage.48

In vivo—Much of the reported clinical information on rhubarb relates to its use as a supportive treatment in cancer rather than as a treatment on its own. With few side-effects it reduced radiation-induced damage in the treatment of lung cancer through modulation of inflammatory cytokines49 and it improved the inflammation and return of gastro-intestinal function in patients treated surgically for gastric cancer.50 To-date there have been almost no reported data from clinical trials on Essiac use in cancer therapy—one recent study failed to find any benefit51—although there are anecdotal reports of efficacy.52,53

Cardiovascular

In vivo—Rheum significantly improved lipid levels54,55 including in patients with atherosclerosis in whom circulatory flow was increased.56

It reduced endothelial damage in women with pregnancy-induced hypertension improving their lipid and immune status.57 In those women at risk for this condition, low doses of the herb had a protective effect against its development.58

Antimicrobial

In vitro—Rheum spp. and individual anthraquinones have a range of antimicrobial activity:-

Emodin's mode of action is associated with disruption of the micro-organisms’ cell membranes.74

In vivo—In treating patients with sepsis the addition of Rheum helped reduce the incidence of opportunistic fungal infection,75 decreased intestinal permeability76 and improved gastro-intestinal perfusion.77 The herb also improved the outcome of systemic inflammatory response syndrome patients with nosocomial (hospital-derived) Gram-negative bacterial pneumonia.78

Rheum and Salvia officinalis together in a topical preparation was as effective as Zovirax for treating of herpes labialis.79

Kidney disease

Rheum has been used in traditional Chinese medicine to help treat renal disease.80

In vitro—It inhibits protein glycation81 (glycation causes nephropathy in diabetes).

In vivo—It was used as part of an effective treatment for nephrotic syndrome complicated by intestinal bleeding.82 There is evidence from clinical trials that low doses of the herb, in conjunction with orthodox medicine, benefited the treatment of chronic renal failure83–87 and improved associated hyperlipidaemia.84,88 This data has been reviewed.89,90

Anti-inflammatory

In vitro—A topical gel containing Rheum and a pharmaceutical antimicrobial inhibited cytokine release, oedema and vasodilation in simulated inflammation of gingival cells.91

In vivo—Rheum used with orthodox treatment in patients with systemic inflammation reaction syndrome reduced inflammatory chemical levels in sera, improving patient outcomes significantly compared to orthodox treatment alone.92

Other

In vitro—Rheum spp.:-

Individual constituents modulate the excessive production of pro-inflammatory cytokines (emodin),97 protect neurons from damage by amyloid protein (a stilbene),98 and may increase insulin sensitivity and energy metabolism in adipocytes (emodin).99

In vivo—Clinical studies have reported that Rheum was of benefit in:-

Medicinal uses

Gastro-intestinal tract

This is the recognized western use of Rheum and whilst the hydroxyanthracene components are purgative their action is much milder than that of Cassia and Aloe spp. The tannins help to give the herb an astringent action, and it is additionally bitter with potential antimicrobial and anti-inflammatory activities. It can be used to treat:-

Traditional Chinese medicinal uses are listed under Historical uses.

Pharmacy

Daily  
Decoction of dried herb –   0.2–4 g
Tincture BPC (60%) –   up to 15 ml
As astringent or stomachic –   0.1–0.3 g
Three times daily  
Fluid extract –   0.5–8 ml (suggested guidelines)

For laxative purposes Rheum should be used short term for a maximum of 2 weeks and can be taken as a single or divided dose. It takes from 6–24 hours after ingestion to act and is usually taken at bedtime.

Doses in above trials ranged from 1.5 ml (this is low dose) to 24 ml of 1:2 extract per day (converted from grams).

Constipation is treated with doses in the higher range as at low dose the effect of the tannins predominates.16

For pharmacokinetic information on anthraquinones see Cassia.

CONTRAINDICATIONS—Intestinal obstruction or abdominal pain of unknown origin.

Precautions and/or safety

In overdose it can cause diarrhoea and griping. Pseudomelanosis coli is associated with overuse of herbs containing anthraquinones including Rheum,106 it is not considered pathologic and is reversible when usage ceases—see Cassia.

Interactions

Because of a decreased transit time through the colon it is possible that Rheum may interact with drugs with which it is co-administered and which are absorbed from this area. There are no reported interactions.

Historical uses

Used for conditions of blood stasis and as peripheral vasodilator, anticoagulant, anti-inflammatory and antimicrobial. Internally to treat gastro-intestinal haemorrhage, jaundice; abdominal pain, indigestion, ulcers; amenorrhoea, dysmenorrhoea, hypertension. Externally for scalds and burns.

Rheum palmatum

Chinese rhubarb, Turkey rhubarb

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Family Polygonaceae

Description

A stout perennial growing from a thick rhizome up to 2 m high in flower. Leaves large, outline rounded, base heart-shaped, with deeply palmate lobes which may be further divided. Flowers, small, greenish white, in panicles in summer.

Habitat and cultivation

R. palmatum is native to China, growing on forest margins in wet soils in high mountainous areas. It is wild harvested and also cultivated.

See above (R. officinale) for Parts used up to Historical uses.

Rumex crispus

Yellow dock, curled dock

Description

A perennial with a stout taproot growing up to about 1 m high in flower. Petiole is shorter than the leaf blade, anterior side flattened with raised margins so that it appears concave. Lamina of lower leaves 6–30 × 1.5–6.5 cm, narrow-lanceolate, oblong or ligulate, undulate with curly margins, leaf base attenuated† Upper leaves similar but smaller. Stem erect, smooth and slender. Inflorescence terminal, nearly simple or with a few erect lateral branches, each subtended by a narrow crisped leaf with whorls of flowers closely bunched. Flowers pale green, small and numerous, male or female or both. Perianth 1–2.5 mm long, segments of outer whorl more or less elliptic, obtuse and not reflexing at fruiting. Segments of inner whorl much longer and enlarging at fruiting. Fruiting valves 3–4.5 × 3–5 mm broad-ovate with raised veins, entire, sinuate or crenulate; tubercles 1–3, deep red, often 1 being much larger. Nuts 2–2.5 mm long, dark brown and sharply angled. Flowers in spring and summer.

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Family Polygonaceae

Habitat and cultivation

Native to Europe, North Africa and West Asia. Naturalised world-wide in both damp and dry places. It self-sows freely. Deep rich damp soil in full sun produces better roots. Drought and frost resistant.

Parts used

The root harvested after the fruit is ripe, towards the end of summer.

Active constituents

1) Hydroxyanthracenes107,108

a) anthraquinones (3–4%) including nepodin, physcion, chrysaphanol, emodin and 1,5-hydroxy isomers of methylanthraquinone.109,110 The chemical make-up and levels depend on genetic and environmental factors

b) anthrone—rumexone110

2) Tannins

3) Volatile oil

Also contains resin and oxalic acid.

Nutritional constituents

Vitamins: A and C

Minerals: Iron, manganese, calcium and phosphorous

Actions

1) Mild cholagogue

2) Laxative

3) Alterative

4) Tonic

Scientific information

There has been no recent investigation into this herb however there are many similarities in chemistry between Rheum and Rumex.

The laxative effects of the anthraquinones are like those found in Cassia and Rheum and as in the latter they are moderated by the relatively high level of tannins. The bitter quality extends its use beyond just a laxative effect. The purgative effect is gentle.

Medicinal uses

Cardiovascular system

Gastro-intestinal tract

Musculoskeletal

Skin

BHP specific for skin diseases, especially psoriasis, with constipation.

Externally

Pharmacy

Three times daily  
Decoction of dried root –   2–4 g
Tincture 1:5 (45%) –   1–5 ml
Fluid Extract (25%) –   2–4 ml

Historical uses

Used “when either the blood or liver is affected by choler”, piles; bleeding from the lungs; diphtheria; scurvy; itchy skin conditions; to treat cancer, tonic for weakened constitutions. Seeds have also been employed to treat dysentery. An ointment used for skin problems like itch; scab; eruptions; freckles; morphews; spots and discolouring.

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†By making stool easier to pass

†This distinguishes it from other common docks.