Rhubarb

Rhubarb is an extremely interesting anthraquinone drug, as it has not only laxative - stimulant properties, but also aperitifs and digestives, always determined by the presence of anthraquinones.

There are several species belonging to the genus Rheum, and are used for both laxative and stimulant and as an aperitif. The most used species are Rheum officinalis and Rheum palmatum ; in particular the most valuable and used variety is the " tanguticum " variety.

Rhubarb is a perennial herbaceous plant of the Poligonaceae family, which has large ovate, long petiolate leaves; the large leaves have a diameter in the widest part of the lamina that can even reach 50-80cm; the long petiole, which must support leaves of this size, is firm and fleshy, and in the variety tanguticum has a reddish base. Every year the rhubarb emits a floral scape, in the center of what is a rosette arrangement of the basal leaves, which brings a panicle to the top. Depending on the varieties and characteristics of the species, this panicle may present a coloration of its flowers red or white, or greenish-white or yellowish-white. The perennial organ is the rhizome and it has a particular herbal importance, in plants that are at least four years old. The rhizome is collected and crushed - in pieces with dimensions varying from 3-5 cm to 7-8cm, rarely 10cm, of various squared or parallelepiped shape - therefore treated for drying. It can be dried on racks or in a stove; the dried product on racks is considered the most valuable; this means that the drying method is an important artificial factor in determining the quality of the drug. Another decisive element for the quality of the rhubarb drug, this time natural, is its origin. The plant, in fact, despite having Chinese origins, is cultivated a little throughout Southeast Asia. The rhubarb of Chinese origin, in particular from Chinese counties on the Atlantic coast or from the China Sea, is the most valuable, to the detriment of drugs from the more internal areas. Rhubarb is a drug that, depending on the different qualities (determined by the age of the plant, the place of origin and the method of drying), can present, to a greater or lesser extent, the following morphological characteristics: the drug has a part inner yellow more or less vivid, which sometimes is characterized by a thin yellow powder; the outer part, instead, characterized by the bark, is black-brown in color, sometimes even eliminated. If we observe the rhubarb drug under the microscope, we can see reddish punctuations, characterized by a different morphology that distinguishes them in supernumerary vascular bundles, typical of a rhizome, and medullary rays or star bodies, structures easily identifiable by the fact that they are surrounded by a amyliferous sheath; this amylifera sheath surrounds particularly reddish cells, which are those that contain anthraquinones and can belong to supernumerary vascular structures or medullary rays. These morphological description criteria are those that must be included in the evaluation of drug quality.

Rhubarb is a source that accumulates large amounts of calcium oxalate and this occurs particularly in the leaves, which are not properly drugs, but are used by certain populations in the production of jams, juices or whatever. The whitish guina can be characterized not only by starch, but also by calcium oxalate crystals, in this case it will be called oxaliferous sheath. Furthermore, rhubarb does not only contain anthraquinones, but also compounds of a flavonoid nature (which make up the yellow powder), and tannins, which are important from a herbalistic point of view because they give the phytocomplex an interesting and versatile use projection compared to other anthraquinone drugs. Rhubarb, therefore, is used as a laxative - stimulant drug, as a digestive and eupeptic drug, but also as a drug with astringent properties, which limits the laxative action of the drug itself. This is also the reason why rhubarb - among the various anthraquinone drugs, in relation to the intensity of the laxative effect and the undesirable effects - is less active from the laxative - stimulant point of view. As anticipated, tannins counteract the activity of anthraquinones, so the effect of the rhubarb phytocomplex is much more easily modulated, in a therapeutic sense, than other drugs. The tannins are present in all the tissues of the drug, except for the red colored structures.

The importance of rhubarb is therefore also linked to the presence of tannins, which make it an anthraquinone drug that can be easily used in terms of dosage. It is also used by the liqueur industry for its bitter-tonic properties.