categoryZCrops Crops List 

RHUBARB

Rheum × rhabarbarum

Dock & Knotweed Family [Polygonaceae]

month8apr month8april month8may

category
category8Crops
 
status
statusZneophyte
 
flower
flower8cream
 
flower
flower8pink
 
morph
morph8actino
 
petals
petalsZ6 tepalsZ6
tepals
type
typeZclustered
 
stem
stem8fluted
 
toxicity
toxicityZmedium
 

16th April 2011, Calder & Hebble Navigation, Wakefield. Photo: © RWD
Being cultivated outside alongside the canal.


8th April 2011, a garden in Hardraw, Hawes, Yorkshire. Photo: © RWD
Leaves large roughly triangular with a satin finish and an un-even appearance.


8th April 2011, a garden in Hardraw, Hawes, Yorkshire. Photo: © RWD
A single leaf atop a single stem. Very large prominent veins underneath support the large leaf.


28th April 2011, a garden in Downham, Lancs. Photo: © RWD
The flowering stalk is separate from the edible (after cooking) leaf stalk (petiole). Clusters of creamy green or reddish pink flowers tower above the leaves by another two feet or so.


28th April 2011, a garden in Downham, Lancs. Photo: © RWD
The foamy cluster of flowers. Each flower has six tepals rather than petals. Note the papery bract that folds out like a handerchief from avery branch in the flowering stem.


11th June 2010, a garden in Glenridding, Cumbria. Photo: © RWD
The leaves are smoothish, triangular to cardioid tapering to a blunt point.


Photo: © Ros Dunlevey
The flowers, somewhat surprisingly, are very similar to those of Docks, with reddish wings on the fruits.


Photo: © Ros Dunlevey
But this is not altogether that surprising when it is realised that Rhubarb belongs to the Dock Family.


Photo: © Ros Dunlevey
Each white flower has six tepals (they aren't petals) and six white stamens with white anthers. The flowers are very much like those of Russian Vine, which belongs to the same family.


24th June 2013, a garden, Walkden, Gtr M/cr. Photo: © RWD
The flat seeds are larger than those of other Docks.


24th June 2013, a garden, Walkden, Gtr M/cr. Photo: © RWD
The seeds have three flat flanges set at 120° to each other. The flanges are light-green with a pale-green halo. The seed sits in the centre and is reddish brown.


17th June 2006, Gobi Desert, Outer Mongolia. Photo: © Phil And Ann Farrer
Wild Rhubarb in its native habitat, the Gobi Desert, which doesn't look un-like Garden Rhubarb. Neither the flowers nor the seeds are usually ever seen, since it is normally advantageous when growing rhubarb stalks for consumption that it should not flower.


A RHUBARB CULTIVAR

probably: Rheum atrosanguineum var. tangaticum

2nd May 2012, Rochdale Canal, Callis Wood, Hebden Bridge. Photo: © RWD
Probably Rheum atrosanguineum var. tangaticum, which is a an ornamental garden rhubarb grown here as a canal-side feature. The leaves are jagged and emerge reddish-green, turning dark green. The massive stem will grow to 2m high and bear white, pink or crimson coloured flowers.


2nd May 2012, Rochdale Canal, Callis Wood, Hebden Bridge. Photo: © RWD
The flowers burst forth from within boxing-glove shaped pouches near the summit. Stems are covered in very short stiff hairs or bristles.


2nd May 2012, Rochdale Canal, Callis Wood, Hebden Bridge. Photo: © RWD
The flower buds are arranged as bunches of bunches.


2nd May 2012, Rochdale Canal, Callis Wood, Hebden Bridge. Photo: © RWD
Un-opened flower buds look much the same as in other varieties.


Uniquely identifiable characteristics

Distinguishing Feature :

Lookee-Likees : Brazilian Giant Rhubarb and Chilean Giant Rhubarb

Flowers very much like those of Russian Vine which belongs to the same Dock and Knotweed Family.

No relation to : Brazilian Giant Rhubarb or Chilean Giant Rhubarb or [plants with similar names and that look a little like Rhubarb, but which belong to the Giant Rhubarb Family (Gunneraceae)]

Is related to: Monk's Rhubarb which belongs to the same Family as Rhubarb, but is in a different Genera (Rumex).

Besides Rhubarb, there exists another related species, Ornamental Rhubarb (Rheum palmatum), which is grown in gardens and parks as an ornamental plant rather than as plant for consumption.

Rhubarb is grown as a crop plant by both farmers and especially by cottage gardeners. The leaves are more toxic (and not eaten) than are the red (or green) crescent-shaped stems. Both contain poisonous Oxalic Acid but the leaves about 40 times more (by weight) and also contain another toxic component thought to be an anthraquinone glycoside.

The edible stalks (petioles) are very bitter because of the presence of Malic Acid, but when boiled with a sugary solution in water become much more palatable.

In the UK it is grown mainly in the so-called 'Wakefield Triangle' which lies between Wakefield, Leeds and Morley, which is where some of the above photographs were taken. It is grown both outdoors, and indoors within darkened sheds when it is harvested by candle-light to keep the best taste. The stalks are sold either green, or in the more popular red; both are as edible after cooking. There are normally two harvests, April to May, and June to July.

One cultivator within the 'Wakefield Triangle' sells a hundred different varieties of Rhubarb, some for consumption, others as a decorative ornamental plant. Some of the ornamentals can be as tall as 8 feet.

ANTHRAQUINOID DYES in RHUBARB


Chrysophanic Acid and Emodin are two anthraquinoid dyes that are present in the roots of Rhubarb. Chrysophanic Acid (also called Rheic Acid, Chrysophanol and Rhubarbarin) is a yellow crystalline substance that is also present in Curled Dock (Rumex crispus) (aka Yellow Dock in the USA) and is used in the treatment of skin diseases. As a dye, it can be used to make yellow, orange and red shades with suitable mordants and is sometimes used as a dye for hair, since Chrysophanic Acid will bind to the keratin in hair. Chrysophanic Acid has spectral absorption peaks at 256nm, 278nm, 288nm and 436nm.

Emodin (1,6,8-Trihydroxy-3-methylanthraquinone) is closely related chemically to Chrysophanic Acid, and is also present in Buckthorn and Japanese Knotweed. The crystals are dull-orange in colour and it is another anthraquinone dye. It may be useful in the treatment of Type 2 Diabetes, and also exhibits anti-cancer effects and has a neuroprotective function against glutamate toxicity.

Rhein (aka Casseic Acid or Rhein-9-Anthrone) is an anthraquinoid acid that is also present in Rhubarb. It is being evaluated as an anti-bacterial agent against Staphyococcus aureus. Both Emodin and Rhien are cathartic and laxative, which helps explain why Rhubarb has been used as a dieting foodstuff in times past.

Physcion aka Parietin is another anthraquinone found in Rhubarb. It has anti-tumour and anti-fungal properties and is orange-yellow in colour. It is the orange pigment found in lichens of the Genus Caloplaca and in Golden Shield Lichen and is also found in the roots of Curled Dock. More recent research suggests it should be useful in treating leukaemiaand it also inhibits the growth of lung head and neck tumours. Parietin inhibits the enzyme 6PGD (6-phosphogluconate dehydrogenase) which is part of the pentose-phoshate pathway responsible for constructing the cellular building blocks necessary for rapid growth. Without these building blocks cancer cells cannot grow., but then, neither can new non-cancerous cells. Clearly, if approved for use in humans (and trials have not yet begun) treatment cannot continue indefinitely.

A STILBENOID in RHUBARB


Stilbenoids are related to Stilbene, the old name for Resveratrol found in grapes and in wine, and was once thought to provide a certain health benefits.

Rhaponticin is the glycoside of the stilbenoid Rhapontigenin and is found in the rhizome roots of Rhubarb. In tests on diabetic mice, Rhaponticin had beneficial effects, but it remains to be determined whether it will exhibit much the same effects in humans. Acting also on beta amyloid plaques within the brain it may also be helpful for use in the treatment of Alzheimers disease. It is not reported whether Rhapontigenin is also found within Rhubarb but this compound shows activity against prostrate cancer cells due to its inhibitory effect on human cytochrome P450, an enzyme thought to transform some cardiogenic and immunotoxic compounds.


  Rheum × rhabarbarum  ⇐ Global Aspect ⇒ Polygonaceae  

Distribution
 family8Dock & Knotweed family8Polygonaceae

 BSBI maps
genus8Rheum
Rheum
(Rhubarbs)

RHUBARB

Rheum × rhabarbarum

Dock & Knotweed Family [Polygonaceae]

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