In botany

Botany

Botany, plant science, or plant biology is a branch of biology that involves the scientific study of plant life. Traditionally, botany also included the study of fungi, algae and viruses...

, the petiole is the stalk attaching the leaf

Leaf

A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....

 blade to the stem

Plant stem

A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence , conifer cones, roots, other stems etc. The internodes distance one node from another...

. The petiole usually has the same internal structure as the stem. Outgrowths appearing on each side of the petiole are called stipule

Stipule

In botany, stipule is a term coined by Linnaeus which refers to outgrowths borne on either side of the base of a leafstalk...

s. Leaves lacking a petiole are called sessile

Sessility (botany)

In botany, sessility is a characteristic of plants whose flowers or leaves are borne directly from the stem or peduncle, and thus lack a petiole or pedicel...

, or clasping when they partly surround the stem. Clasping leaves of the Poaceae

Poaceae

The Poaceae is a large and nearly ubiquitous family of flowering plants. Members of this family are commonly called grasses, although the term "grass" is also applied to plants that are not in the Poaceae lineage, including the rushes and sedges...

 have an extra structure called the ligule

Ligule

A ligule — is a thin outgrowth at the junction of leaf and leafstalk of many grasses and sedges or a strap-shaped corolla, such as that of a ray floret in plants in the daisy family....

. Petiolate leaves are ones where the petiole connects to the leaf before its apex.

In some plants, the petioles become flattened and widened, and the true leaves may become reduced or vanish altogether. These are known as phyllodes or phyllodia, or cladophylls. Thus, the phyllode comes to serve the purpose of the leaf. Phyllodes are common in the genus Acacia

Acacia

Acacia is a genus of shrubs and trees belonging to the subfamily Mimosoideae of the family Fabaceae, first described in Africa by the Swedish botanist Carl Linnaeus in 1773. Many non-Australian species tend to be thorny, whereas the majority of Australian acacias are not...

, especially the Australian species, at one time put in Acacia subgenus Phyllodineae. Sometimes, especially on younger plants, partially formed phyllodes bearing reduced leaves can be seen.

In Acacia koa, the phyllodes are leathery and thick, allowing the tree to survive stressful environments. The petiole allows partially submerged hydrophytes to have leaves floating at different depths; the petiole being between the node and the stem.

Etymology

Petiole is and comes from Latin

Latin

Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 petiolus, or peciolus "little foot," "stem", an alternate diminutive

Diminutive

In language structure, a diminutive, or diminutive form , is a formation of a word used to convey a slight degree of the root meaning, smallness of the object or quality named, encapsulation, intimacy, or endearment...

of pes "foot." The regular diminutive pediculus is also used for "foot stalk".