Summarizing Leaves

Summary

Leaves are the main site of photosynthesis. A typical leaf consists of a lamina (the broad part of the leaf, also called the blade) and a petiole (the stalk that attaches the leaf to a stem). The arrangement of leaves on a stem, known as phyllotaxy, enables maximum exposure to sunlight. Each plant species has a characteristic leaf arrangement and form. The pattern of leaf arrangement may be alternate, opposite, or spiral, while leaf form may be simple or compound. Leaf tissue consists of the epidermis, which forms the outermost cell layer, and mesophyll and vascular tissue, which make up the inner portion of the leaf. In some plant species, leaf form is modified to form structures such as tendrils, spines, bud scales, and needles.

Glossary

compound leaf

leaf in which the leaf blade is subdivided to form leaflets, all attached to the midrib

cuticle

waxy protective layer on the leaf surface

lamina

leaf blade

palmately compound leaf

leaf type with leaflets that emerge from a point, resembling the palm of a hand

petiole

stalk of the leaf

phyllotaxy

arrangement of leaves on a stem

pinnately compound leaf

leaf type with a divided leaf blade consisting of leaflets arranged on both sides of the midrib

sessile

leaf without a petiole that is attached directly to the plant stem

simple leaf

leaf type in which the lamina is completely undivided or merely lobed

stipule

small green structure found on either side of the leaf stalk or petiole

venation

pattern of veins in a leaf; may be parallel (as in monocots), reticulate (as in dicots), or dichotomous (as in Gingko biloba)

whorled

pattern of leaf arrangement in which three or more leaves are connected at a node

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