Lettuce (Lactuca sativa) undergoes a transformation as it matures, moving through a complete life cycle that is easily observed. This cool-season crop exhibits different appearances depending on its age and variety. The plant’s development is marked by clear shifts in size, leaf structure, and overall form.
From Seed to Rosette: Initial Development
Growth begins after the oblong seeds absorb water and germinate, typically taking two to fifteen days to produce a small, delicate seedling. The initial set of leaves, known as cotyledons, are typically rounded or oval and look nothing like the mature leaves of the plant.
Cotyledons serve as the plant’s first food source until the first true leaves appear, marking the beginning of the vegetative stage. These true leaves possess the characteristic shape and texture of the mature variety. As more leaves develop, they arrange themselves in a low, circular pattern known as the rosette stage. This compact cluster of foliage maximizes light absorption while keeping the growing point close to the ground. This stage of rapid leaf growth forms the foundation of the mature plant.
Distinct Appearance of Mature Lettuce Types
The visual difference in mature lettuce is most pronounced across its main categories, which affect both the growth habit and texture.
Loose-leaf Varieties
Loose-leaf varieties, such as Black-Seeded Simpson or Red Leaf, do not form a head. Instead, they present as an open, sprawling mound of leaves. The leaves are often ruffled, crinkled, or deeply lobed, exhibiting colors from bright green to deep burgundy and red tips. This open growth habit allows for a continuous “cut-and-come-again” harvest of the outer leaves.
Butterhead Varieties
Butterhead types, including Bibb and Boston lettuce, form a soft, almost buttery appearance. The leaves are tender, often crinkly, and fold over one another gently, resembling a loosely formed flower or a small cabbage. Bibb varieties form a smaller, cup-shaped head, while Boston forms a slightly larger, more open head. The innermost leaves are often pale and particularly tender.
Romaine Varieties
Romaine lettuce, also known as Cos, grows in an upright, vertical structure. The leaves are long, paddle-shaped, and form a loaf-like or columnar head. They are recognized for their pronounced, firm central spine, which contributes to their characteristic crunch. While some varieties form a closed, tight head, all Romaine maintains this tall structure.
The Final Stage: Bolting and Flowering
When growing conditions become unfavorable, typically due to increasing heat or longer daylight hours, the plant transitions to reproduction. This process is known as bolting. The central stem, previously short and hidden among the leaves, begins to elongate rapidly, shooting upwards to become a tall, rigid stalk.
As the stalk rises, the leaves often shrink, change shape, and develop a bitter flavor. The stalk will eventually produce small flower heads, which are typically yellow and resemble miniature dandelions, as lettuce belongs to the daisy family. Once the plant bolts, vegetative growth stops, and the plant becomes tall and woody as it prepares to set seed.