The lima bean, the edible seed of the leguminous plant Phaseolus lunatus, is a widely cultivated crop known for its distinctive flat, kidney shape. The size of this seed exhibits significant variability, which is primarily a function of its genetic lineage but is also influenced by specific growing conditions. This wide range in physical dimensions is so pronounced that commercial markets have developed separate classifications to differentiate the available types.
Categorization of Lima Beans by Size
The difference in lima bean size stems from two independent domestication events that occurred in different regions of the Americas. The large-seeded varieties trace their origin to the high-altitude Andes region, while the small-seeded types were developed in the lowlands of Mesoamerica. This genetic divergence established the two main categories that define the market today: large-seeded and small-seeded.
The small-seeded types are marketed as “Baby Limas” or Sieva beans, a category that includes varieties like Henderson and Dixie. These beans are generally rounder and flatter than their larger counterparts and are associated with bush-type plants that mature relatively quickly. In contrast, the large-seeded varieties, frequently called Fordhook or Butter Beans, are derived from the Andean gene pool. These larger beans are grown on pole-type vines and require a longer growing season to reach their full size.
Physical Dimensions and Measurement
A mature, dried lima bean can vary significantly in length, ranging from approximately 1 centimeter (0.4 inches) up to 3 centimeters (1.2 inches) in the largest varieties. The largest dried types, sometimes exceeding an inch, are sourced from the original Andean lineage.
In commercial processing, particularly for canned beans, a standardized system based on width measurements is used to sort the product. This system utilizes sieves or screens, with sizing expressed in 64ths of an inch. For example, “Petite” lima beans are those that pass through a screen 28/64ths of an inch wide, while the “Large” designation is reserved for any bean wider than 38/64ths of an inch. This method of classification ensures consistency for consumers and processors.
Size’s Influence on Culinary Use
The physical size of the lima bean directly impacts its performance and texture once cooked. Smaller beans, such as the baby lima varieties, have a greater surface area to volume ratio, which allows for faster water absorption and heat penetration. This results in a shorter cooking time, sometimes taking only an hour to simmer after soaking, and a finished product that is described as having a more tender and creamier texture.
The larger, thicker Fordhook and Butter Bean types require more time to cook through, sometimes needing up to two hours of simmering to reach the desired tenderness. These larger beans tend to have a higher starch content and a thicker seed coat, which contributes to a finished texture often described as starchy or mealy, rather than creamy. This textural difference makes the large types suitable for dishes where a firmer, more potato-like consistency is preferred.
Environmental Factors Affecting Final Size
While genetics determine the potential size of a lima bean, environmental factors regulate whether that potential is fully realized. The most sensitive period for size determination occurs during the flowering and subsequent pod-filling stages of the plant’s growth cycle. High air temperatures, especially those exceeding 90°F, can negatively affect pollination and fertilization.
When temperatures are too high, the plant may abort flowers and developing pods, resulting in smaller seeds. High night temperatures are also detrimental, as they increase the rate of respiration, which consumes energy the plant needs to allocate to seed growth and filling.
Water availability is another limiting factor. Prolonged drought stress during the critical pod-filling stage can significantly reduce the final size and weight of the mature seed.