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In this article we will discuss about Leaf:- 1. Types of Leaf 2. Phyllotaxy 3. Simple Leaf 4. Compound Leaf 5. Leaf Shapes 6. Apex of Leaf 7. Leaf Margins.
Contents:
- Types of Leaf
- Phyllotaxy
- Simple Leaf
- Compound Leaf
- Leaf Shapes
- Apex of Leaf
- Leaf Margins
1. Types of Leaf:
i. Seed leaves:
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These are the cotyledons present on the seed.
ii. Foliage leaves:
Flat, green, lateral appendages developing on stem or branch.
iii. Scaly leaves:
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Scale like, small, stalkless, non- green leaf. It is also called cataphyll.
iv. Bract leaves or Hypsophylls:
These are present at the base of flower of inflorescence.
v. Prophylls:
These are bracteoles.
vi. Ligule:
These are finger – like small parts present at the upper end of leaf sheath.
vii. Floral leaves:
Calyx, corolla, stamens and carpels.
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viii. Sporophylls:
Spore – bearing leaves of pteridophytes, gymnosperms and angiosperms.
2. Phyllotaxy:
The arrangement of leaves on the stem (Fig. 68) is called phyllotaxy.
It is following three different categories:
i. Alternate:
When only one leaf develops at each node, e.g., Brassica campestris, Nicotiana tabacum.
It is following types:
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(a) Distichous or 1/2 or 2- ranked:
When 3rd leaf comes over the first one, e.g., grasses.
(b) Tristichous or 1/3 or 3-ranked:
When 4th leaf comes over the first one, e.g., Cyperus.
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(c) Pentastichous or 2/5 or 5-ranked:
When 6th leaf comes over the first one after completing two revolutions of the spiral, e.g., apple.
(d) Octostichous or 3/8 or 8-ranked:
When 9th leaf comes over the first one after completing three revolutions of the spiral, e.g., Carica papaya.
ii. Opposite:
When a pair of leaves are present just opposite to each other at each node, e.g., Calotropis.
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It is of following types:
(a) Opposite and decussate:
When two successive pairs of leaves occur at right angle to each other, e.g., Psidium.
(b) Opposite and superposed:
When all the pairs of leaves occur in the same plane, e.g., Combretum.
iii. Whorled:
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When more than two leaves are arranged in the form of a whorl at each node the phyllotaxy is called whorled, e.g., Hydrilla verticillata, Nerium, etc.
3. Simple Leaf:
A leaf consisting of single entire or divided blade, but the divisions of the blade are not so deep as to reach down upto the midrib (Fig. 69).
4. Compound Leaf:
When the divisions of the leaf blade or lamina are so deep so as to reach upto the midrib and the leaf is divisible into many segments or leaflets, it is called compound leaf (Fig. 69). A compound leaf may be of following two types: pinnately compound leaf or palmately compound leaf.
(A) Pinnately Compound Leaf:
When the leaflets are arranged along the sides of the midrib or rachis.
It may be of following types:
i. Unipinnate:
When the leaflets are present directly on the mid-rib.
It is again of following two types:
(a) Paripinnate:
When even number of paired leaflets are present, e.g., Tamarindus indica.
(b) Imparipinnate:
When an odd terminal leaflet is present, e.g., Murraya.
ii. Bipinnate:
When mid-rib produces secondary axis and on the latter are present the leaflets, e.g., Delonix regia.
iii. Tripinnate:
When the mid-rib produces the secondary axis and the later produces the tertiary axis which bears the leaflets, e.g., Oroxylum, Moringa oleifera etc.
iv. Decompound:
When the leaf is more than thrice pinnate, e.g., Foeniculum, Daucas, etc.
(B) Palmately Compound Leaf:
When the leaflets of the leaf are attached in one plane, just at the apex of the petiole, giving the appearance of palm of hand.
It is of following types:
i. Unifoliate:
When the apex of the petiole is articulated by a single leaflet, e.g., Berberis vulgaris (Fig. 69).
ii. Bifoliate:
When the apex of petiole is articulated by two leaflets, e.g., Bauhinia saigonensis (Fig. 69).
iii. Trifoliate:
When 3 leaflets are present, e.g., Aegle (Fig. 69).
iv. Quadrifoliate:
When 4 leaflets are present, e.g., Marsilea (Fig. 69).
v. Multifoliate or digitate:
When more than 4 leaflets are present (Fig. 69), e.g., Lupinus.
5. Leaf Shapes:
1. Acicular:
Long and needle like, e.g., Onion, Pinus roxburghii.
2. Linear:
Long, flat and narrow, e.g., grasses.
3. Lanceolate:
Lance-shaped, broad and tapering either at both the ends or generally towards the apex, e.g., Nerium indicum.
4. Subulate:
It is an awl -shaped leaf, e.g., Isoetes.
5. Oblanceolate:
Broad in the middle and tapering towards both the ends, e.g., Gnaphalium.
6. Elliptical:
Ellipse-shaped with both the ends rounded, e.g., Psidium, Carissa, etc.
7. Ovate:
Egg shaped, i.e. broad at the base and narrowing towards apex, e.g., Hibiscus rosasinensis.
8. Obovate:
It is inversely ovate, i.e., upper end broader narrowing towards the base (Fig. 70), e.g., Artocarpus.
9. Oblong:
Long, wide with parallel-running margins, e.g., Banana.
10. Cordate:
Heart-shaped, e.g., Piper betel.
11. Obcordate:
Inversely cordate, e.g., Oxalis.
12. Rotund:
When blade is circular, e.g., Lotus.
13. Reniform:
Kidney-shaped (Fig. 70), e.g., Centella asiatica.
14. Spathulate:
Spathula-shaped, i.e., broad and round at the top and narrowing towards the base, e.g., Drosera.
15. Oblique:
When two halves of the lamina are unequal, e.g., Azadirachta, Melia, etc.
16. Sagittate:
When leaf blade is like an arrow (Fig. 70), e.g., Sagittaria sagittifolia.
17. Hastate:
When two basal lobes of a sagittate leaf become pointed and directed outward, e.g., Ipomoea.
18. Cuneate:
Wedge-shaped leaf with lower narrow end, e.g., Pistia stratiotes.
19. Lyrate:
When the leaf blade is like a lyre, i.e., contains a big terminal lobe and many smaller lateral lobes, e.g., Raphanus sativus.
20. Falcate:
When the shape is like a sickle (Fig. 70), e.g., Eucalyptus globulus.
21. Pedate:
Like the claw of a bird, e.g., Vitis pedata.
22. Lorate:
When the shape is like a narrow strip of leather, e.g., Vallisneria.
23. Auriculate:
When the leaf blade is ear-shaped, e.g., Magnolia fraseri (Fig. 70).
6. Apex of Leaf:
i. Acute:
Ending into a sharp point in the form of an acute angle, e.g., Mangifera indica.
ii. Acuminate:
When apex is drawn out in the form of a long slender tail, e.g., Ficus religiosa.
iii. Cuspidate:
When apex a terminates into a long, sharp, spiny point, e.g., Phoenix sylvestris.
iv. Obtuse:
Ending into a blunt, rounded end, e.g., Cassia obtusifolia.
v. Truncate:
Ending abruptly as if cut transversely straight (Fig. 71), e.g., Bauhinia anguina.
vi. Retuse:
It is like obtuse with a shallow notch, e.g., Pistia stratiotes.
vii. Emarginate:
Apex containing a deep notch (Fig. 71), e.g., Bauhinia.
viii. Mucronate:
Rounded apex ending abruptly into a short point, e.g., Calotropis gigantea.
ix. Cirrhose:
Apex ending into a tendril-like structure, e.g., Gloriosa superba (Fig. 71).
7. Leaf Margins:
1. Entire:
Even and smooth, e.g., Ficus benghalensis.
2. Repand:
Wavy in appearance, e.g., Polyalthia longifolia.
3. Serrate:
Sharp, small teeth – like outgrowths pointing upward, e.g., Rosa.
4. Biserrate:
When each tooth of the serrated margin is again serrated.
5. Serrulate:
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When the teeth in serrate margins are very minute, e.g., Croton.
6. Dentate:
When teeth project outwards at right angle to the edge, e.g., Nymphaea nouchali.
7. Runcinate:
When teeth of the serrated margins are pointing backwards.
8. Crenate:
When teeth are rounded, e.g., Bryophyllum.
9. Ciliate:
Provided with fine projecting hair, e.g., Corchorus olitorius.
10. Spinous:
Provided with projecting spines, e.g., Argemone.
11. Incised:
Provided with sharp and irregular incisions.
12. Lobed:
Provided with many lobes, e.g., Ranunculus.
