leaf blade types, leaf margin types and leaf base types

Leaf blade types

Shape of the Lamina or Leaf Blade with reference to general outline, the following types are noted :

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(A) Acicular — When the leaf blade is very long, narrow and cylindrical having the shape of a needle, e.g. Pinus sp. (Pinaceae).

(B) Linear — When the leaf blade is long, narrow and flat i.e. blades are slightly broader, e.g. in many grasses, Polyanthes tuberosa (Amaryllidaceae) etc.

(C) Lanceolate — When the leaf blade has the shape like that of a lance i.e. leaf blade is wider in the middle and narrower towards the apex and base, e.g. Bambusa arundinacea (Gramineae), Polygonum barbatum (Polygonaceae), Nerium sp. (Apocynaceae) etc.

(D) Oblong — When the leaf blade is wide and long with two margins running parallel e.g. Musa sp (Musaceae), Colutea arborescens (Papilionaceae) etc.

(E) Subulate or Awl-shaped — When the leaf blade is long, narrow and gradually tapers from base to apex, e.g. Ulex europaeus (Papilionaceae), Salsola kali (Chenopodiaceae), Isoetes sp. (Pteridophyte), etc.

(F) Ovate — When the leaf blade is egg-shaped e.g. leaf blade broader at the base than at the apex, e.g. Hibiscus rosa-sinensis (Malvaceae), Solanum nigrum (Solanaceae), etc.

(G) Obovate — When the leaf blade is inversely egg-shaped i.e. leaf blade broader at the apex than at the base, e.g. Terminalia catappa (Combretaceae), Cassia obovata (Caesalpinaceae), etc.

(H) Spathulate — When the leaf blade is broad and round at the apex and tapering narrowly towards the base, e.g. Bellis perennis (Compositae), Drosera burmannii (Droseraceae), Phyla nodiflora (Verbenaceae) etc.

(I) Cordate — When the leaf blade is heart-shaped, with deep notch at the base e.g. Piper betle (Piperaceae), Sida cordifolia (Malvaceae), Ficus religiosa (Moraceae) etc.

(J) Obcordate — Opposite of cordate, i.e. when the leaf blade is inversely heart-shaped e.g. Bauhinia variegata (Caesalpinaceae), Oxalis corniculata (Oxalidaceae) etc.

(K) Sagittate — When the leaf blade is arrow-shaped i.e. the apex of the leaf blade is pointed and two basal lobes are pointed downwards, e.g. Sagittaria sagittifolia (Alismaceae), Ipomoea reptans (Convolvulaceae) etc.

(L) Hastate — When the leaf blade has two pointed basal lobes directed outwards, e.g. Typhonium trilobatum (Araceae).

(M) Reniform — When the leaf blade is kidney-shaped i.e. the apex of the leaf blade is rounded above with a deep notch at the base, e.g. Centella asiatica (Umbelliferae).

(N) Lunate — When the leaf blade has the shape like a half-moon with two pointed basal lobes, e.g. Passiflora lunata (Passifloraceae), Adiantum lunatum (Pteridophyte) etc.

(O) Cuneate — When the leaf blade is wedge-shaped, flattened and broad with a narrow base e.g. Pistia stratiotes (Araceae).

(P) Rotund or Orbicular — When the leaf blade is nearly circular e.g. Nelumbo nucifera (Nymphaeaceae), Tropeolum majus (Tropaeolaceae) etc.

(Q) Elliptical — When the leaf blade is more or less like an ellipse, e.g. Lochnera rosea (Apocynaceae), Ficus elastica (Moraceae) etc.

(R) Falcate — When the leaf blade is sickle-shaped e.g. Eucalyptus globulus (Myrtaceae). Arundinaria falcata (Gramineae) etc.

(S) Incised form — Besides the above mentioned shapes of the leaves, the shape of the leaf may be of different types due to varieties of incision of the blade. When the leaf blade has a large and rounded terminal lobe, and two or more smaller lateral lobes towards the base, it is called lyrate e.g. Raphanus sativus, Brassica nigra etc. of Cruciferae. When the lobes of the blade are arranged like the claw of a bird, it is called pedate, e.g. Vitis pedata (Vitaceae).

Leaf Margins

The shape of the margin of leaf lamina or leaf blade is dependent on the extent to which the leaf blades are subject to varieties of incisions, cuts or irregularities or completely free from them. The following leaf margin types are recognised :

1. Entire leaf margin — In this type, the leaf margin is even and smooth, entire leaf margin example – Mangifera sp. (Anacardiaceae), Artocarpus sp. (Moraceae), Musa sp. (Musaceae), Ficus sp. (Moraceae), Anona reticulata (Anonaceae) etc.

2. Repand or Undulate — When the leaf margin is undulating or wavy; e.g. Polyalthia longifolia (Anonaceae), Mimusops elengii (Sapotaceae) etc.

3. Serrate leaf margin — When the margin of lamina is incised like the teeth of a saw, e.g. Hibiscus rosa-sinensis (Malvaceae), Azadirachta indica (Meliaceae), Rosa sp. (Rosaceae), etc.

4. Serrulate — A margin representing the diminutive of serrate, finely serrate, e.g. Symplocos ramsissima (Symplocaceae), Trema orientalis (Ulmaceae).

5. Double serrate — Small and large teeth are alternating with each other, e.g. Sida acuta (Malvaceae).

6. Dentate leaf margin — When the teeth of the leaf lamina are sharp and projected outwards almost at right angles to the margin, e.g. Nymphaea esculenta (Nymphaeaceae).

7. Crenate leaf margin — When the margin is toothed but the teeth are rounded e.g., Centella asiatica (Umbelliferae), Kalanchoe binnata (Crassulaceae).

8. Spiny — Margin of the leaf blade with large teeth-like projections ending in spines, e.g. Argemone mexicana (Papaveraceae).

9. Bi-serrate — When the margin is toothed but the teeth are again serrated e.g. Ulmus campestris (Ulmaceae).

10. Bi-dentate — When the margin is toothed and the teeth are again dentate. e.g. Castanopsis indica, Quercus dentata (Fagaceae) etc.

11. Bi-crenate — The margin is toothed and the large rounded teeth are again crenate on their margin.

12. Lobed leaf margin — When the margins of the blades are more deeply divided than in the above instances, the divisions are then generally called lobes and the margins of the leaf blade lobed or incised, e.g. species of Papaver (Papaveraceae), Chrysanthemum (Compositae) etc.

Types of Venation – Difference between Parallel and Reticulate Venation

Leaf base Types

The base of leaf is usually the end of attachment. Different types of leaf bases are found which are discussed below:—

(a) Attenuate — When the lower sides constricting concavely and into wing-like petiole.

(b) Cuneate — When leaf base becomes narrow to broad wedge-like taper, acute and the sides become straight.

(c) Oblique leaf base — When the lowermost sides of the leaf base become unequal.

(d) Obtuse — When the leaf base is round and constricting abruptly to the petiole.

(e) Truncate — Here the leaf base with a nearly straight line across the bottom, as if cut across.

(f) Cordate — When the two lobes of the leaf base gives a heart-shaped appearance.

(g) Auriculate leaf base — When leaf base looks like a small ear-like lobe (auricle) on either side of the petiole and the auricles are separated by a narrow sinus. In Calotropis procera, the leaf is sessile, here the two lobes surround the stem like two flaps and the base is called auriculate.

(h) Amplexicaul — This term is often used when the auriculate leaf base completely clasps the stem.

(i) Perfoliate — When the basal lobes of the leaf lamina fuse together after completely clasping the stem as if the stem has pierced the leaf e.g. Bupleurum.

(j) Connate — When the basal lobes of the two opposite leaves fuse together after completely clasping together and looks like one leaf, the stem passing through the centre of leaf, e.g. Canscora.

(k) Sagittate leaf base — When a pair of basal lobes turned downwards and inwards, their apices being acute or obtuse.

(l) Hastate — When a pair of basal lobes are deeply incised and the lobes are flaring outward.