• The rhubarb plant has a conical rootstock which is yellow on the inside and fleshy. The roots and rhizomes contain ‘star-shaped’ spots (2.5mm – 4mm) in the pith.
• In general rhubarb roots has a firm texture, with a bright yellow surface having white reticulations. The roots and rhizomes are generally not shrunken.
• The white reticulations are due to fusiform cut ends of the medullary rays (colored reddish brown) when observed against the phloem parenchyma (white). Different species have different depths of medullary rays, for example, the palmatumtype has only 6 cells deep medullary rays, while the officinale has as much as 200 cells deep rays. These medullary rays give a red and white lines appearance in the officinale species and can be useful in determining quality of rhubarb.
• Rhubarb quality can be determined macroscopically into three grades based on their fracturing:

1. Shensi/Chinghai type or High Grade– High grade rhubarb when fractured gives a marbled or ‘nutmeg’ fracture.  Also it has a characteristic bright pink color upon fracturing. The powder of such grade of rhubarb is generally bright yellow.

2. Canton type or Medium Grade– The general characteristics are similar to high grade except for lesser attention has been given to its preparation. Fracturing such a rhubarb gives a more granular fracture which is a pale pink color. Poor trimming and greyish patches on the outer surface yields a medium grade rhubarb.

3. Third Grade– The size of the rhubarb in this grade is generally smaller. Fracturing such rhubarb yields a brownish grey color fracture which also yields a less yellow powder.

• Calcium oxalate rosettes (up to 200 µm in diameter) are found abundantly in the leaf blades.
• Compound starch grains are also present.
• The reticulate vessels and other wood elements present in Rhubarb shows absence of lignin.
• The anthraquinone derivatives (yellow content) present in the medullary ray cells when treated with ammonia turn reddish pink and deep red when treated with caustic alkalis.

2. Anthraquinones with a carboxy group– Rhein and its glycoside, glucorhein.

3. Anthrones or dianthrones of emodin or physcion or chrysophanol or aloe-emodin.

4. Heterodianthrones obtained from two different anthrones– Combination of aloe-emodin anthrone and emodin anthrone (Palmidin A), combination of aloe-emodin and chrysophanol anthone (Palmidin B), combination of emodin anthrone and chrysophanol anthrone (Palmidin C).

The R. palmatum species contains sennosides as well for purgative action.

Chemical Test for Rhaptonic Rhubarb- macerate powdered rhaptonic rhubarb with 10mL of 45% ethanol (or other alcohol) for 20 minutes. Filter this solution and spot this filtrate on a filter paper and observe under UV light. Rhaptonic rhubarb gives a distinct blue colored fluorescence. The official test given in the BP requires a TLC to be performed.

Uses- Rhaponticin is found to be useful as antithrombotic, antiallergic and antidiabetic in preliminary studies.

Other proposed uses of the drug include:

• Prevents progression of chronic renal failure in patients with high serum creatinine.
• Has a lipid lowering effect due to its high fiber content. Exerts its effects on cholesterol by inhibiting squalene epoxidase.
• Shows antiplatelet activity.
• Has antifungal, antibacterial and molluscidal properties
• Treats neonatal jaundice