Rheum is a genus of about 60 perennial plant

Perennial plant

A perennial plant or simply perennial is a plant that lives for more than two years. The term is often used to differentiate a plant from shorter lived annuals and biennials. The term is sometimes misused by commercial gardeners or horticulturalists to describe only herbaceous perennials...

s in the family Polygonaceae

Polygonaceae

Polygonaceae is a family of flowering plants known informally as the "knotweed family" or "smartweed family"— "buckwheat family" in the United States. The name is based on the genus Polygonum and was first used by Antoine Laurent de Jussieu in 1789 in his book, Genera Plantarum. The name refers...

. The genus includes the vegetable rhubarb

Rhubarb

Rhubarb is a group of plants that belong to the genus Rheum in the family Polygonaceae. They are herbaceous perennial plants growing from short, thick rhizomes. They have large leaves that are somewhat triangular-shaped with long fleshy petioles...

 (Rheum rhabarbarum or Rheum x hybridum.) The species have large somewhat triangular shaped leaves

Leaf

A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....

 with long, fleshy petiole

Petiole (botany)

In botany, the petiole is the stalk attaching the leaf blade to the stem. The petiole usually has the same internal structure as the stem. Outgrowths appearing on each side of the petiole are called stipules. Leaves lacking a petiole are called sessile, or clasping when they partly surround the...

s. The flower

Flower

A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...

s are small, greenish-white to rose-red

Rose (color)

Rose is the color halfway between red and magenta on the HSV color wheel, also known as the RGB color wheel, on which it is at hue angle of 330 degrees.Rose is one of the tertiary colors on the HSV color wheel...

, and grouped in large compound leafy inflorescence

Inflorescence

An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...

s. A number of varieties of rhubarb have been domesticated both as medicinal plants and for human consumption. While the leaves are toxic, the stalks are used in pies and other foods for their tart flavor.

Description

Rheum species are herbaceous perennials growing from fleshy roots. They have upright growing stems and mostly basal, deciduous leaves growing from short, thick rhizome

Rhizome

In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...

s. They have persistent or deciduous ocrea. The inflorescences are terminal and panicle-like with pedicels. The hermaphrodite flowers consist of a whitish green to pinkish green, hairless and campanulate perianth, composed of six tepals. The outer three tepals are narrower than the inner three and all are sepal-like in appearance. The flower

Flower

A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...

s have nine (sometimes six) stamina

Stamen

The stamen is the pollen producing reproductive organ of a flower...

 inserted on the torus at the base of the peranthium, they are free or subconnatent at their base. The anthers are yellow or pinkish green, elliptic in shape. The ovary

Ovary (plants)

In the flowering plants, an ovary is a part of the female reproductive organ of the flower or gynoecium. Specifically, it is the part of the pistil which holds the ovule and is located above or below or at the point of connection with the base of the petals and sepals...

 is simple and triangular shaped with three erect or deflexed styles

Gynoecium

Gynoecium is most commonly used as a collective term for all carpels in a flower. A carpel is the ovule and seed producing reproductive organ in flowering plants. Carpels are derived from ovule-bearing leaves which evolved to form a closed structure containing the ovules...

. The stigmas are head-like. The fruit

Fruit

In broad terms, a fruit is a structure of a plant that contains its seeds.The term has different meanings dependent on context. In non-technical usage, such as food preparation, fruit normally means the fleshy seed-associated structures of certain plants that are sweet and edible in the raw state,...

s are a three-sided achene

Achene

An achene is a type of simple dry fruit produced by many species of flowering plants. Achenes are monocarpellate and indehiscent...

 with winged sides, and the seed

Seed

A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...

s are albuminous with a straight or curved embryo

Embryo

An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

.
The name has its origin in the Ancient Greek

Ancient Greek

Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...

 word rheon, which was used by Dioscorides, possibly for a plant in this genus.

Species

The genus is represented by about 60 extant species. Among species found in the wild, those most commonly used in cooking are the garden rhubarb (R. rhabarbarum) and the so-called false rhubarb (R. rhaponticum), which is actually a true rhubarb. The many varieties of cultivated rhubarb more usually grown for eating are recognised as Rheum x hybridum in the Royal Horticultural Society

Royal Horticultural Society

The Royal Horticultural Society was founded in 1804 in London, England as the Horticultural Society of London, and gained its present name in a Royal Charter granted in 1861 by Prince Albert...

's list of recognised plant names. The drug rheum is prepared from the rhizomes and root

Root

In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...

s of another species, R. officinale

Rheum officinale

Rheum officinale is a rhubarb from the family Polygonaceae originating in Asia.-Medicinal uses:The root and stem of R. officinale are used to treat constipation, as well as to aid in the dissolution of blood clots and pus eruptions...

or medicinal rhubarb. This species is also native to Asia, as is the turkey rhubarb

Turkey rhubarb

Rheum palmatum, commonly called Turkey rhubarb, Chinese rhubarb, Indian rhubarb, Russian rhubarb or rhubarb root , is a highly regarded medicinal plant, known for its health benefits.-Description:The species ““R. tanguticum”” and ““R...

 (R. palmatum). Another species, the Sikkim rhubarb (R. nobile), is limited to the Himalayas

Himalayas

The Himalaya Range or Himalaya Mountains Sanskrit: Devanagari: हिमालय, literally "abode of snow"), usually called the Himalayas or Himalaya for short, is a mountain range in Asia, separating the Indian subcontinent from the Tibetan Plateau...

.

Rheum species have been recorded as larva

Larva

A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

l food plants for some Lepidoptera

Lepidoptera

Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...

 species including brown-tail

Brown-tail

The brown-tail is a moth of the family Lymantriidae. It is distributed throughout Europe.The wings of this species are pure white, as is the body, apart from a tuft of brown hairs at the end of the abdomen. The brown coloration extends along most of the back of the abdomen in the male...

, buff ermine

Buff Ermine

The Buff Ermine is a moth of the family Arctiidae. It is sometimes placed in the genus Spilosoma. It is found throughout the temperate belt of the Palearctic region south to Northern Turkey, Georgia, Kazakhstan; also in Southern Siberia , Eastern Mongolia, Amur Region, China, Korea and Japan.The...

, cabbage moth

Cabbage Moth

Note: the Small White species of butterfly is commonly called a "cabbage moth" in North America.The Cabbage Moth is a common European moth of the family Noctuidae....

, large yellow underwing

Large Yellow Underwing

The Large Yellow Underwing is a moth, the type species for the family Noctuidae. It is an abundant species throughout Europe, one of the most common and most familiar moths of the region. In some years the species is highly migratory with large numbers appearing suddenly in marginal parts of the...

, and nutmeg moth

Nutmeg (moth)

The nutmeg , also known as the clover cutworm, is a moth of the family Noctuidae. It is found throughout Europe although in the north of its range it is a summer migrant, not being able to survive the cold winters.This is a small to medium species with cryptically coloured forewings, varying from...

.

Uses

Many rheum species have food and medicinal uses. Some of these uses originated in Asia more than 2,000 years ago. Rheum rhabarbarum is used to make pies, jellies, jams, and wine. All parts of the plant contain the poison

Poison

In the context of biology, poisons are substances that can cause disturbances to organisms, usually by chemical reaction or other activity on the molecular scale, when a sufficient quantity is absorbed by an organism....

 oxalic acid

Oxalic acid

Oxalic acid is an organic compound with the formula H2C2O4. This colourless solid is a dicarboxylic acid. In terms of acid strength, it is about 3,000 times stronger than acetic acid. Oxalic acid is a reducing agent and its conjugate base, known as oxalate , is a chelating agent for metal cations...

, but its concentration in the leaf stems or petioles used in food preparation is very low, and their tart flavor instead is caused by nontoxic malic acid

Malic acid

Malic acid is an organic compound with the formula HO2CCH2CHOHCO2H. It is a dicarboxylic acid which is made by all living organisms, contributes to the pleasantly sour taste of fruits, and is used as a food additive. Malic acid has two stereoisomeric forms , though only the L-isomer exists...

, The plants also produce other poisonous compounds, including citric acid

Citric acid

Citric acid is a weak organic acid. It is a natural preservative/conservative and is also used to add an acidic, or sour, taste to foods and soft drinks...

 and anthraquinone

Anthraquinone

Anthraquinone, also called anthracenedione or dioxoanthracene is an aromatic organic compound with formula . Several isomers are possible, each of which can be viewed as a quinone derivative...

 glycosides, and the raw or cooked leaf blades are poisonous to humans and livestock if consumed in large enough amounts. Plants in cultivation are propagated by cutting up the crowns of larger plants and by seeds.

Some species are grown for their ornamental qualities, including R. acuminatum, R. alexandrae, R. australe, R. kialense, R. palmatum, R. rhabarbarum and R. ribes.