Rhubarb is a hardy perennial plant, known for its tart, edible stalks. Correct identification of the plant’s parts is important for culinary use and safety. The main structure consists of a crown at the soil line, from which the edible stalks and the large, inedible leaves emerge. Understanding the specific appearance of the leaf blade is the first step in safely utilizing this spring crop.
Visual Characteristics of the Leaf Blade
Rhubarb leaves are immediately recognizable due to their considerable size and distinct structure. The leaf blade, the broad, flat, green portion, can reach two feet (60 centimeters) or more in width on a mature plant. This expansive surface area helps the plant maximize light absorption.
The shape is typically triangular or broad and heart-shaped, sometimes featuring deep lobes. The surface often has a slightly crinkled or heavily textured appearance, which contributes to its robust look. Prominent veins radiate outward from the stalk connection point, with the central vein being noticeably thick and providing significant structural support.
The color is generally a deep, vibrant green. The veins and edges may sometimes show a reddish tint, especially near the attachment point. This large, dark foliage stands in strong contrast to the colorful stems below it.
Distinguishing Leaves from Edible Stalks
Differentiating the large leaf blade from the edible stalk, or petiole, is necessary before consumption. The petiole is the long, fleshy structure connecting the leaf blade to the plant’s base. It is the only part of the rhubarb plant commonly consumed, known for its tart flavor and crisp texture.
The edible stalks are thick, succulent, and rigid, often displaying colors that range from pale green to deep red, depending on the variety. Stalks can grow up to 18 inches long and two inches in diameter, providing a substantial, firm structure.
In contrast, the leaf blade is thin, broad, and floppy once detached, serving as the plant’s major photosynthetic organ. When harvesting, the correct procedure involves cutting or pulling the stalk away from the crown and discarding the entire leaf blade attached to the end of the stalk. Recognizing the difference between the fleshy, firm petiole and the thin, broad, dark green blade is the primary safety distinction.
Toxicity and Safety Concerns
The strict separation of the leaf and stalk is due to the high concentration of a toxic compound within the leaf blade. Rhubarb leaves contain significant levels of oxalic acid, which makes them inedible for human consumption. The concentration in rhubarb leaves is high enough to be problematic.
Ingesting the leaf material can lead to a condition known as oxalate toxicity. Symptoms of this poisoning can include burning in the mouth and throat, nausea, vomiting, and abdominal pain. In more severe cases, the accumulation of calcium oxalate crystals can interfere with kidney function, potentially leading to kidney stones or even kidney failure.
The leaves should be discarded entirely and never cooked or processed for food. The small amount of oxalic acid present in the edible stalks is generally considered safe, especially when cooked, but the leaf blade must be completely removed to eliminate the risk of poisoning.
Growth Pattern and Plant Arrangement
Rhubarb is a robust herbaceous perennial that grows from a subterranean structure called a crown. The leaves and stalks emerge directly from this crown in the early spring, forming a dense, circular pattern known as a basal rosette.
The leaves shoot upward and then arch outward, creating a large, imposing clump that can measure four to five feet wide. The sheer size of the foliage means rhubarb requires ample space in a garden setting, as the leaves naturally shade the ground around the plant. As the season progresses, the massive leaves help the plant conserve moisture.
This dense, mounding arrangement is characteristic of a mature rhubarb plant. The foliage dies back to the ground each winter, only for new, tightly furled leaves to emerge from the crown in the following spring as temperatures rise.