Basic About Leaves : Classification

Leaves are borne on a stem in a definite fixed order, or phyllotaxy, according to species . For identification purposes, leaves are classified according to type and shape, and types of margins , tips and bases , and venation . 

Leaf arrangement. (a) Helical (top view). (b) Helical with elongated internodes (alternate). (c) Opposite (decussate). (d) Whorled (verticillate).

Leaf types. (a) Simple. (b) Trifoliate. (c) Palmately compound. (d) Odd-pinnately compound. (e) Even-pinnately compound. (f) Decompound.

Leaf shapes. (a) Linear. (b) Lanceolate. (c) Oblanceolate. (d) Spatulate. (e) Ovate. (f) Obovate. (g) Elliptic. (h) Oblong. (i) Deltoid. (j) Reniform. (k) Orbicular. (l) Peltate. (m) Perfoliate. (n) Connate.

Leaf margins of various types. (a) Entire. (b) Serrate. (c) Serrulate. (d) Dentate. (e) Denticulate. (f) Crenate. (g) Undulate. (h) Incised. (i) Pinnatifid. (j) Dissected. (k) Lobed. (l) Cleft. (m) Parted.

Leaf tips and bases. (a) Acuminate. (b) Acute. (c) Obtuse. (d) Truncate. (e) Emarginate. (f) Mucronate. (g) Cuspidate. (h) Cuneate. (i) Oblique. (j) Cordate. (k) Auriculate. (l) Sagittate. (m) Hastate. (n) Clasping.

Leaf venation. (a) Dichotomous. (b) Pinnate reticulate. (c) Palmate reticulate. (d) Parallel (expanded leaf). (e) Parallel (linear leaf).

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