petiolus

Petiolus is a botanical term used to describe a small stalk that connects a leaf blade to the stem. The word comes from Latin and is often treated as a diminutive form of the leaf stalk, or petiole. In practice, a petiolus denotes a leaf stalk that is markedly short, sometimes nearly reduced to a mere connector, while a typical leaf with a longer stalk is described simply as having a petiole.

Morphology and terminology. A petiolus serves the same basic function as a petiole: to position the leaf blade for photosynthesis and to allow some control of blade orientation. When the stalk is very short, some authors consider the leaf to be subsessile, while others still refer to a petiolus. If the stalk is entirely absent, the leaf is described as sessile. The distinction between a petiolus and a standard petiole is therefore a matter of length and contextual usage rather than a separate anatomical structure.

Usage and context. The term petiolus is relatively uncommon in modern English-language botany and is more frequently encountered in older floras, Latin diagnoses, or highly specialized taxonomic descriptions. Most contemporary texts prefer the more general terms petiole or sessile, depending on whether a stalk is present and its length.

See also. Petiole, Sessile leaf, Pedicel, Peduncle, Plant morphology.

Notes. As with many Latin-based terms, usage may vary by author, and some sources may treat petiolus as a near-synonym of a very short petiole.