Lehtiset

Lehtiset is a Finnish botanical term referring to the leaflets that constitute a compound leaf. In plant morphology, a compound leaf is divided into multiple leaflets (lehtiset) that are connected to a central axis, or rachis, rather than to the main stem. Lehtiset may be arranged pinnately (along a central rachis) or palmately (radiating from a single point). The individual lehtiset can vary in size, shape, and margin, and they may be sessile (without a distinct stalk) or have a short petiolule that attaches them to the rachis.

The term is used in Finnish floras and field guides to describe leaf anatomy without specifying the plant species. It is not a taxonomic rank; rather, it is a descriptive term referring to leaf architecture. Common plant groups with compound leaves and leaflets include many members of the Fabaceae (legumes), as well as several other families such as Rosaceae (some genera with pinnate leaves) and Aesculus (palmate leaflets).

In terminology, lehtiset are distinguished from individual leaves, which are the entire photosynthetic units attached to the stem. Understanding leaf structure, including the arrangement and characteristics of lehtiset, helps in plant identification and in studies of photosynthetic efficiency and adaptation.