Rhubarb's Botanical Family: Polygonaceae
Many culinary enthusiasts are surprised to learn that rhubarb (scientifically classified as Rheum rhabarbarum) is not a fruit, but a vegetable. Even more surprising is its botanical lineage. Rhubarb belongs to the family Polygonaceae, commonly known as the knotweed or buckwheat family. This group of flowering plants is known for their distinctive swollen nodes or "knees" on the stems, which is where the name Polygonaceae comes from (meaning "many knees"). While buckwheat is a common culinary member of this family, the relation between the two isn't always obvious to the casual observer. However, exploring the botanical connections reveals a surprising network of relatives that share more than just a family name.
What is the Polygonaceae (Buckwheat) Family?
The Polygonaceae family is a diverse group of plants with a worldwide distribution. Members range from herbs and shrubs to small trees. A defining feature, in addition to the stem nodes, is the presence of ochrea, a sheath-like stipule that wraps around the stem at the base of the leaf. The edible members of this family are often prized for their tart or slightly sour flavor profiles, which is particularly true for rhubarb and sorrel. The family also contains many well-known and even some invasive species, such as Japanese knotweed, highlighting its broad reach. The shared characteristics across this family provide a strong foundation for understanding why rhubarb has the taste and texture it does.
Other Notable Members of the Polygonaceae Family
Beyond rhubarb, several other plants within the Polygonaceae family have culinary or medicinal uses, revealing the shared ancestry and characteristics.
- Buckwheat (Fagopyrum esculentum): A pseudo-cereal whose grain-like seeds are used to make flour, noodles, and groats. Despite its name, it is not a type of wheat and is gluten-free.
- Sorrel (Rumex acetosa): A leafy green herb with a bright, lemony, and slightly acidic flavor, often used in salads, soups, and sauces. Its tartness is a direct parallel to rhubarb's own flavor profile.
- Knotweed (Polygonum species): While some species are invasive, others are cultivated for their culinary or ornamental value.
- Docks (Rumex species): Certain species of dock, such as broad-leaved dock, have edible leaves when young, though they contain oxalic acid like rhubarb leaves.
The Great Rhubarb Debate: Fruit or Vegetable?
The question of whether rhubarb is a fruit or a vegetable is one of the most common culinary head-scratchers. While botanically a perennial vegetable, its common usage as a dessert ingredient has created lasting confusion. For legal and historical reasons, this distinction has been blurred over time.
Why the Culinary Confusion?
The main source of confusion stems from a 1947 U.S. Customs Court ruling. To avoid higher taxes on vegetables at the time, the court legally reclassified rhubarb as a fruit because it was primarily used in desserts, such as pies, tarts, and jams. This ruling, while purely for tax purposes, solidified its culinary reputation as a fruit, even though it remains a vegetable in the eyes of botanists. In many other parts of the world, no such distinction was made, and rhubarb is still treated as a vegetable.
The Anatomy of a Rhubarb Plant
Rhubarb is a herbaceous perennial that grows from thick rhizomes. It is most recognized for its long, fleshy, edible stalks (known as petioles) that range in color from crimson red to light green, depending on the variety. However, the anatomy of the plant also includes large, somewhat triangular leaves that are highly toxic to humans and animals.
Key Parts of the Rhubarb Plant
- Stalks (Petioles): The edible part of the plant, prized for its tart flavor in cooking. The color of the stalks does not indicate ripeness but is a characteristic of the specific variety.
- Leaves: The large, triangular leaves contain high levels of oxalic acid and anthrone glycosides, making them poisonous. They should always be discarded.
- Rhizomes: The thick, underground root system from which the plant grows each spring.
- Flowers: Rhubarb can produce a tall flower stalk, which many gardeners remove to redirect the plant's energy towards producing larger, more robust edible stems. The flowers themselves are edible but can be quite tart.
A Quick Comparison: Rhubarb vs. Celery
Due to their similar stalk-like appearance, rhubarb is sometimes confused with celery, but they are from entirely different plant families and have distinct characteristics. The following table outlines the key differences:
| Feature | Rhubarb | Celery | Botanical Family | Polygonaceae (Knotweed/Buckwheat Family) | Apiaceae (Carrot Family) | Edible Part | Stalks (Petioles) only; leaves are toxic | Stalks, leaves, and seeds are edible | Flavor Profile | Very tart and acidic; often cooked with sugar | Mild, savory, and slightly bitter | Texture | Fibrous but breaks down when cooked | Crisp and crunchy | Growth Habit | Forms large, sprawling crowns | Grows in a tight, upright bunch | Nutritional Highlight | Excellent source of Vitamin K and fiber | Rich in Vitamin A, folate, and sodium |
Nutritional Profile and Health Benefits
Beyond its unique family and culinary identity, rhubarb offers several health benefits. It is a good source of fiber, which is important for digestive health, and is notably high in Vitamin K. Vitamin K is essential for bone health and proper blood clotting. Rhubarb also contains a significant number of antioxidants, including anthocyanins (which give red varieties their color) and proanthocyanidins. These compounds have antibacterial, anti-inflammatory, and potentially anti-cancer properties. The vegetable is also low in calories, making it a nutritious addition to many recipes, especially when the added sugar is controlled. The root of the rhubarb plant has been used for centuries in traditional Chinese medicine for its laxative and anti-inflammatory effects, though modern usage focuses more on the edible stalks.
Conclusion
Rhubarb's placement in the Polygonaceae, or buckwheat, family is a core botanical fact that sheds light on its relationships with other plants, like sorrel and buckwheat. This understanding helps clarify the long-standing debate over whether it's a fruit or vegetable, confirming its identity as a perennial vegetable despite its common culinary application in sweet dishes. Acknowledging its proper classification and its relationship to other plants underscores the complexity and rich history of the food we eat, while also reminding us to only consume the safe, edible stalk. Whether used in a classic pie or a modern savory dish, rhubarb remains a unique and flavorful ingredient with a fascinating botanical story.
- For more information on rhubarb cultivation and varieties, an excellent resource is the University of Wisconsin Extension article on the plant: Rhubarb, Rheum rhabarbarum - Wisconsin Horticulture.
How to Safely Prepare Rhubarb
To safely prepare rhubarb, the key is to only use the fleshy, edible stalks. Before cooking, ensure all leaves are completely removed and discarded, as they are toxic due to high levels of oxalic acid. You can then wash the stalks and chop them to the desired size for your recipe. Peeling is not typically necessary unless the outer layer is particularly tough or blemished. Rhubarb is most commonly cooked with sugar to balance its intense tartness, making it suitable for desserts like pies, jams, and crumbles.
The Rhubarb Triangle
In the United Kingdom, there is a famous area known as the "Rhubarb Triangle," located between Leeds, Wakefield, and Morley. This region is historically known for producing forced rhubarb by growing it in special, dark, heated sheds. This method produces tender, pink-hued stalks much earlier in the season than outdoor-grown varieties, and the hand-harvesting is traditionally done by candlelight to avoid disrupting the growth process. The Rhubarb Triangle highlights the specialized cultivation and cultural significance of this vegetable in certain regions.
Tips for Growing Rhubarb at Home
Growing rhubarb is a relatively straightforward process for home gardeners, particularly in cooler climates where the plant thrives. It is a hardy and long-lived perennial, capable of producing for up to a decade. Here are a few tips for success:
- Choose a Location: Plant rhubarb in a location that receives full sun and has well-drained soil.
- Initial Growth: Allow the plant to establish itself for at least one full year before the first harvest.
- Harvesting: Pull stalks from the base of the plant instead of cutting them. Avoid harvesting more than half the stalks at a time to ensure the plant remains healthy.
- Flowering: Remove any flower stalks that emerge to encourage the plant to put its energy into growing stronger stems.
A Global History of Rhubarb
Rhubarb has a rich history that spans both medicinal and culinary uses across continents. Originally from Asia, it was used medicinally in China as far back as 2700 BC, primarily as a purgative. The dried roots were an expensive import for centuries, and it wasn't until the 18th and 19th centuries, with the increasing availability and affordability of sugar, that rhubarb began its rise as a popular food item in Europe and North America. The transition from a medicinal herb to a dessert staple is a key part of its story, making it one of the most interesting vegetables to have on your plate.
