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Section A. Structure and Specialized Characters:
[A. Leaf Parts] [B. Leaf Types] [C. Leaf Structural Types] [D. Petiole and Petiolule Structural Types] [E. Stipule and Stipel Types]
- Blade. Flat, expanded portion of leaf.
- Leaflet. A distinct and separate segment of a leaf.
- Ligule. An outgrowth or projection from the top of the sheath, as in the Poaceae.
- Midrib. The central conducting and supporting structure of the blade of a simple leaf.
- Midvein. The central conducting and supporting structure of the blade of a leaflet.
- Petiole. Leaf stalk.
- Petiolule. Leaflet stalk.
- Pulvinus. The swollen base of a petiole or petiolule.
- Rachilla. Secondary axis of compound leaf.
- Rachis. The main axis of a pinnately compound leaf.
- Sheath. Any more or less tubular portion of the leaf surrounding the stem or culm, as in the Poaceae.
- Stipels. Paired scales, spines, or glands at the base of petiolule.
- Stipules. Paired scales, spines, glands, or blade-like structures at the base of a petiole.
Note: This classification is based on discrete segments of leaves or leaflets, but the terms with "compound" are equally applicable to segments, divisions, etc. of any structure with a blade; e.g., palmately divided, pinnately cleft, etc.
- Bifoliolate, Geminate, or Jugate. With two leaflets from a common point.
- Bigeminate, Bijugate. With two orders of leaflets, each bifoliolate; doubly paired.
- Bipalmately Compound. With two orders of leaflets, each palmately compound.
- Bipinnately Compound. With two orders of leaflets, each pinnately compound.
- Biternate. With two orders of leaflets, each ternately compound.
- Compound. With leaf divided into two or more leaflets.
- Decompound. A general term for leaflets in two or more orders - bi-, tri-etc. - pinnately, palmately, or ternately compound.
- Imparipinnately Compound. Odd-pinnately compound, with a terminal leaflet.
- Interruptedly Pinnately Compound. With smaller and larger leaflets alternating along the rachis.
- Palmately Compound. With leaflets from one point at end of petiole.
- Palmate-pinnate. With first order leaflets palmately arranged, second order pinnately arranged.
- Paripinnately Compound. Even-pinnately compound, without a terminal leaflet.
- Pinnately Compound. With leaflets arranged oppositely or alternately along a common axis, the rachis.
- Simple. With leaf not divided into leaflets.
- Tergeminate. With three orders of leaflets, each bifoliolate, or with geminate leaflets ternately compound.
- Ternately Compound. With leaflets in three's.
- Trifoliolate. With leaflets three, pinnately compound with terminal petiolule longer than lateral; or palmately compound with petiolules equal in length.
- Tripalmately Compound. With three orders of leaflets, each palmately compound.
- Tripinnately Compound. With three orders of leaflets, each pinnately compound.
- Triternate. With three orders of leaflets, each ternately compound.
- Unifoliolate. With a single leaflet with a petiolule distinct from the petiole of the whole leaf, as in Cercis.
- Bract. Modified leaf found in the inflorescence.
- Bracteole or Prophyllum. Small leaf, usually on a pedicel.
- Chaff or Pale. Scale or bract at base of tubular flower in composites.
- Complete. Leaf with blade, petiole, and stipules.
- Cotyledon. Embryonic leaf.
- Elaminate. Without blade.
- Epetiolate. Without petiole, leaf sessile.
- Epetiolulate. Without petiolule, leaflet sessile.
- Epicalyx. Group of leaves resembling sepals below the true calyx.
- Exstipellate. Without stipels.
- Exstipulate. Without stipules.
- Fly Trap. Hinged, insectivorous leaf, as in Dionaea.
- Glume. Bract, usually occurring in pairs, at the base of the grass spikelet.
- Incomplete. Leaf without one or more parts: blade, petiole, stipules.
- Lemma. Outer scale subtending grass floret.
- Palea. Inner scale subtending grass floret.
- Phyllary. One of the involucral leaves subtending a capitulum, as in composites.
- Phyllodium. Flattened blade-like petiole or midrib.
- Pitcher. Ventricose to tubular insectivorous leaf, as in Sarracenia.
- Scale. Small, non-green leaf on bud and modified stem.
- Spathe. An enlarged bract enclosing an inflorescence.
- Spine. Sharp-pointed petiole, midrib, vein, or stipule.
- Sporophyll. A spore bearing leaf.
- Storage Leaf. Succulent, fleshy leaf.
- Tendril. Usually a coiled rachis or twining leaflet modification.
- Tentacular. Glandular-haired or tentacle-bearing insectivorous leaf, as in Drosera.
- Channelled or Canaliculate. With a longitudinal groove.
- Inflated. Swollen or thickened, as in Eichhornia.
- Pericladial. With a sheathing base, as in the Apiaceae.
- Petiolate. With a petiole.
- Petiolulate. With a petiolule.
- Phyllodial. Flattened and blade-like.
- Pulvinal. With a swollen base, as in the Fabaceae.
- Sessile or Absent. Without petiole or petiolule.
- Winged. With flattened blade-like margins.
E. Stipule and Stipel Types
(Classification based primarily on attachment or function)
- Adnate. With stipule attached to petiole.
- Basal. With stipules attached near base of petiole.
- Interpetiolar. With connate stipules from two opposite leaves.
- Lateral. With stipules adnate to petiole and free part of stipules located along the petiole.
- Median. With stipules adnate to petiole with free part of stipules near middle of petiole.
- Photosynthetic. Blade-like and green.
- Sheathing or Protective. Enclosing a bud or flower.
- Stipellate. With stipels.
- Stipulate. With stipules.
- Vestigial. Minute; a remnant.
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