feuilles

Feuilles are the primary photosynthetic organs of most land plants, typically borne on stems and connected by a petiole to a blade called the lamina. They vary widely in size, shape, color, and arrangement and may be simple or compound.

Anatomy and morphology: The lamina is the broad, flat surface that contains chloroplasts for photosynthesis. A network of veins provides structural support and transports water, minerals, and sugars; venation can be reticulate in many dicots or parallel in many monocots. The epidermis often bears a cuticle and stomata, openings regulated by guard cells that control gas exchange and water loss. Leaves may have stipules, a midrib, and a petiole of varying length. Simple leaves have a single blade; compound leaves are divided into leaflets in patterns such as pinnate or palmate.

Variation and adaptations: Leaves exhibit diverse margins (entire, serrate, lobed) and shapes (oval, lanceolate, needle-like). They may be evergreen or deciduous, and drought- or frost-tolerant forms may have a thick cuticle, pubescence, sunken stomata, or succulence. In aquatic species, leaves can be large and flexible to aid buoyancy, while shade leaves are often thinner with larger surface area.

Development and ecology: Leaves originate from the shoot apical meristem as leaf primordia and establish phyllotaxis patterns that influence canopy light capture. Beyond photosynthesis, they contribute to transpiration, cooling, and, in some species, storage or defense.

Etymology and usage: In French, feuilles is the plural of feuille, meaning leaf, sheet, or page.