2. LEAF
• Leaves are the thin and flat lateral outgrowths from
stem nodes.
• They are the main vegetative organs of a plant body,
concerned with photosynthesis, transpiration and gas
exchange.
• Leaves are produced from a superficial meristematic
tissue, called leaf primordia and hence they are
exogenous in origin.
• The part of the stem that bears leaf is called the
node.
• Each leaf possesses an axillary bud at its axil.
3. • In many cases, the same plant bears different kinds of leaves.
• This condition is known as heterophylly.
• It is quite common among hydrophytes (e.g.. Limnophila
heterophylla).
• Here, the submerged part of the shoot bears dissected leaves
and the aerial part bears entire leaves.
• Some terrestrial plants may also have two types of leaves
(e.g., coriander)
• Leaves show great variations in size, form, outline, surface
texture, etc.
• In size, they vary from minute scales to the exceptionally large
leaves of certain palms, which are sometimes 40 feet long.
• In form, some leaves are more or less circular, some others
are long and narrow, but most leaves are of intermediate
shape.
6. Parts of a Dicot leaf
• A typical dicot leaf has three parts, namely
• Leaf base or Hypopodium
• Leaf stalk or Mesopodium
• Leaf lamina or Epipodium.
7. (a) Leaf base
• Leaf base is the initial part of a leaf that attaches to the
stem.
• The upper angle between the leaf base and the stem is
called axil.
• In some plants (e.g., Leguminosae), leaf base is swollen
and is called pulvinus.
• Leaves with pulvinus are called pulvinate leaves (e.g.,
Mimosa pudica, Mangifera indica).
• Pulvinus is responsible for the sleep movement of
leaves (nyctinasty) in Mimosa.
• In monocot leaves, leaf base has a sheath-like
expansion, called sheathing leaf base (e.g., banana,
grasses).
• It partially or completely encircles the stem.
8. • In many dicots, a pair of leafy lateral outgrowths are
given out from the leaf base. They are called stipules.
• Stipules usually protect the developing buds.
• Leaves with stipules are called stipulate leaves (e.g.,
Hibiscus, Ixora), and
• those without stipules are called exstipulate leaves
(e.g., Mangifera).
• Stipules are believed to protect the developing
embryonic leaf.
• Occasionally, they may get modified to enclose the leaf
bud (e.g., Ficus).
11. (b) Leaf stalk
• Leaf stalk is the slender middle part that connects
the lamina with the base.
• The stalk of a simple leaf is called petiole, and that
of a compound leaf is called rachis.
• In some cases, leaves are without stalk and they are
called sessile leaves (e.g., Calotropis, Zinnia).
• A leaf having petiole is called petiolate leaf (e.g.,
Hibiscus, Ficus).
• In some plants, petiole is wing-shaped (e.g., Citrus).
12. (e) Leaf lamina
• Lamina, or leaf blade, is the green, thin and expanded part of
the leaf.
• It is actively involved in photosynthesis, respiration and
transpiration.
• Its tip is called leaf apex, and the edge or border is called leaf
margin.
• Petiole extends throughout the length of the lamina as a
strong vein, called mid-vein or mid-rib.
• Mid-rib gives our bilateral branches to both sides. They are
called veins.
• Veins, in turn, irregularly branch and re-branch into veinlets.
• Mid-rib, veins and veinlets form a network which constitutes
the structural frame work of the leaf lamina
13. • Also serves as the vascular strands or channels for
the transport of organic food, water and minerals.
• Apex and margin of the lamina are variously
shaped.
• Leaf margin is entire and smooth in some cases.
(e.g. banana, grasses).
• In some others, it is toothed or serrated. (e.g.
Hibiscus.)
• In yet others, it is lobed (e.g. tapioca), or wavy and
uneven (e.g. Polyalthia)
• Leaf surface is smooth or curved, with a waxy
coating.
• In some cases, it may bear hairs.
17. Monocot leaf
• Monocot leaf is similar to dicot leaf in its basic morphology.
• It also has the three parts leaf base, petiole and lamina.
• Leaf base is sheathing in monocots.
• It partially on completely encircles the stem.
• Petiole is absent in grasses.
• In some palms, it is modified into a rachis.
• In some monocots, there is a pair of small outgrowths from
the junction between the leaf base and petiole.
• They are called ligules (e.g., grasses)
• The lamina of monocot leaves is isobilateral (lower and
upper sides similar )
• Venation is parallel in monocot leaves.
19. Venation
• Venation is the pattern of arrangement of veins in the leaf blade.
• There are two kinds of venation, namely reticulate venation and
parallel venation .
• In reticulate venation the veins and veinlets form an anastomosing
network
• In parallel venation veins are parallel to one another.
• Parallel venation is horizontal in some cases (e.g. banana), and
longitudinal in others (e.g. bamboo and other grasses, lilies).
• Reticulate venation is characteristic of dicot leaves, and parallel
venation is characteristic of monocot leaves.
• However, there are exceptions. For example, dicots, such
Calophyllum, Alstonia and Eryngium, show parallel venation, and
monocots, such as aroids, Dioscorea (climbing yam), etc. show
reticulate venation.
20.
21. Kinds of leaves
• Based on the number of lamina, or the nature of
the incision of lamina, two kinds of leaves can be
recognized,
•Simple leaves
•Compound leaves
22. (a) Simple leaves
• These are the leaves with only a single lamina
(e.g., Hibiscus).
• In this case, the lamina is entire or incised, but
the incision does not touch the mid-rib nor
does it reach the tip of the petiole.
23.
24. (b) Compound leaves
• These are the leaves whose lamina is divided into
segments, called leaflets or pinnae.
• Unlike leaves, leaflets are devoid of buds or stipules in
their axils.
• Individual leaflets may be stalked or sessile, and free
from each other.
• At the same time, all of them are connected to a
common stalk, called rachis.
• A compound leaf resembles a branch, and each leaflet
of it resembles a simple leaf.
• Yet, a compound leaf differs from a branch in the
absence of terminal and axillary buds and in its
development from a node; a branch develops from the
axillary bud of a leaf.
25.
26. Types of compound leaves
• There are two types of compound leaves, namely
•Pinnately compound
•Palmately compound.
27. 1. Pinnately compound leaves
• These are the compound leaves in which leaflets
are arranged biserially in two ranks on both the
sides of the rachis.
• This is similar to the arrangement of the pinna or, of
a bird's feather. e.g., Neem (Azadirachta indica),
Moringa.
• There are 4 type of pinnately compound leaves.
• They are unipinnate, bipinnate, tripinnate and
decompound leaves.
28. (1) Unipinnate or simple pinnate leaves
• These are the pinnately compound leaves in which the
rachis bears leaflets in opposite or sub-opposite pairs.
• There are two types of unipinnate leaves
• They are paripinnate and imparipinnate.
• In paripinnate leaves, leaflets are paired and hence
even-numbered and the rachis ends in a pair of them
e.g. Tamarindus, Vicia
• In imparipinnate leaves, leaflets are odd-numbered and
the rachis ends in a single leaflet. e.g., rose, neem,
Murraya.
29.
30. (ii) Bipinnate leaves
• These are the pinnately compound leaves in which
the primary rachis beans secondary axes, called
rachillae, which bear leaflets on both the sides.
• So, the leaves pinnate twice.
• e.g. Acacia, Mimosa pudica.
31.
32.
33. (iii) Tripinnate leaves
• These are the pinnately compound leaves in which
the primary rachis gives out secondary rachi which,
in turn, give out tertiary rachi to which leaflets are
attached, So, the leaves pinnate thrice
• e.g. Moringa.
34.
35. (iv) Decompound leaves
• These are the 2 types Pinnately compound leaves
and Palmately compound leaves
1. Pinnately compound leaves
• Pinnately compound leaves in which the tertiary
rachi undergo further branching so that the leaves
pinnate more than thrice.
• e.g. Coriander.
36. 2. Palmately compound leaves
• Palmately compound leaves are the leaves in which
leaflets radiate from the tip of the rachis, just like
the fingers on palm.
• They are of five kinds, namely
1. Unifoliate
2. Bifoliate
3. Trifoliate
4. Quadrifoliate
5. Multifoliate.
37. Unifoliate leaves are the palmately
compound leaves with only a single
leaflet e.g. Citrus.
41. Multifoliate or digitate leaves have
more than four terminal leaflets. e.g.
Bombax (silk cotton), tapioca.
42.
43. Differences between compound
leaves and branches
Compound leaf Branch
Not divided into nodes and
internodes
Divided into nodes and internodes
Axillary buds are absent in the
axils of leaflets
Axillary buds are present in the axils
of leaves
Terminal bud is absent Terminal bud is present
Bears leaflets on a branching rachis Bears leaves at nodes
Will not bear flowers and fruits Will bear flowers and fruits
44. Shape of leaf lamina
• Leaf lamina exhibits incredible variations in its shape. Some of
the common types of lamina or leaves are the following.
1. Linear: Lamina is long and narrow - e.g., grasses.
2. Lanceolate: Lamina is lance-shaped, long and tapering at the
ends, but broadest near the stalk - e.g., Bamboosa, Nerium,
Gloriosa.
3. Oblanceolate: Lamina is lanceolate, but its broadest part is
near the apex - e.g.,Calamus (cane).
4. Elliptical: Lamina is tapering at ends, but broad in the middle,
just in the form of an ellipse - e.g., Vinca, Guava.
45. 5.Oblong: Lamina is two or three times as long as it is broad, with its
side or less parallel and the ends rounded -e.g., plantain, Ixora.
6.Ovate: Lamina is egg-shaped, i.e., slightly broader at the base than
at the apex - e.g., banyan.
7.Obovate : Lamina is inversely ovate, with the broader part near the
apex – e.g., Tectona, Terminalia.
8.Orbicular or rotund: Lamina is more or less circular – e.g., Lotus.
9.Cordate: Lamina is heart-shaped - e.g., Thespesia.
10.Obcordate: Lamina is inversely heart-shaped - e.g., the leaflets of
Oxalis
11.Reniform: Lamina is kidney-shaped, with a broad shallow
depression at the base - e.g., Centella.
12.Cuneate or wedge-shaped: Blade is broadest beyond the middle
and tapen straight down - e.g., Oxalis.
46. 13. Deltoid: Lamina is broadly cuneate, - e.g., Abutilon.
14. Sagittate: Lamina is shaped like an arrow head, with two sharp
and straight lobes at the base - e.g., Sagittaria and Arum.
15.Falcate or sickle-shaped: Lamina is curved sideways - e.g., adult
leaves of Eucalyptus.
16.Oblique: Right and the left halves of the blade are not
symmetrical-e.g., Begonia and Guazuma.
17. Pinnatifid or pinnatisect : Lamina is cut about half-way towards
the mid-rib he into a number of pinnately arranged lobes.
18. Lyrate: Lyre-shaped and pinnatifid lamina, with a much enlarger
terminal lobe and smaller lateral lobes, e.g., Mustard.
19. Acicular: Lamina is needle-shaped, long, narrow and cylindrical,
e. g., Allium
20. Lorate or loriform: Lamina is strap-shaped, e.g., Vallisnaria.
47.
48. Margin of the leaf
• Leaf margin is variously modified, ornamented, or sculptured in
different species. Some common types of leaf margin are the
following.
1. Entire: Margin is even and smooth - e.g., Mangifera.
2. Serrate: Toothed and sow-like margin, with pointed and upwardly
projecting teeth. e.g., Balsam and Acalypha.
3.Dentate: Toothed margin, armed with numerous sharply pointed,
triangular and outwardly pointing teeth - e.g., Hibiscus. This differs
from denticulate margin only in having less fine teeth.
4.Cenate: Margin with rounded and forwardly printing teeth. - e.g.,
Bryophyllum, Stachytarpheta.
5. Undulate or sinuate: Wavy margin- e.g., Polyalthia.
49. 6. Spiny: Margin provided with spines - e.g., pine-apple, Aloe.
7. Glandular: Margin with sticky glandular hairs - e.g., Jatropha
glandulifera.
8. Ciliate: Margin bearing fine cilia-like projecting hairs - e.g.,
Cleome viscosa.
9. Fid or fidus: Broken margin with numerous clefts which
extend half-way from the margin to the midrib, dividing the
lamina into a number of segments or lobes.
(a) Pinnately fid - e.g., radish, mustard.
(b) Palmately fid - e.g., castor, papaya.
10. Sectile: Margin with cuts which extend nearly to the midrib.
(a) Pinnatisect - e.g., Ipomoea quamoclit
(b) Palmatisect - e.g., tapioca, rubber.
50. Apex of the leaf
• Some of the common types of leaf apices are the following:
1. Acute: Leaf tip is sharply ending and abruptly pointed. - e.g.,
Mangifera
2. Acuminate (caudate): Leaf apex progressively narrows to a long
and slender tail and ultimately ends in a point. - e.g., Ficus
religiosa
3. Obtuse: Blunt or rounded leaf apex - e.g., banyan and jack.
4. Cuspidate : Leaf tip ends in a long, rigid and spiny point, e.g., pine
apple.
5. Mucronate: Rounded apex, terminating abruptly in a short and
sharp point e.g., Caesalpinia, Crotalaria.
6. Retuse: Bluntly rounded apex, with a shallow central notch-e.g..
Calophyllun
7. Emarginate: Leaf tip with a deep notch or depression at the tip-
e.g., Bauhenia biloba.
51.
52. Surface of the leaf
• Some of the common types of leaf surfaces are the following:
1. Glabrous: Smooth and shiny surface –
e.g., Ficus religiosa, Vinca
2. Pubescent: Surface is covered with short and soft hairs,
e.g., Hibiscus
3. Villous: Surface is thickly covered with soft and long hairs.
4. Hispid: Surface is covered with stiff hairs,
e.g., Spermacoce.
5. Scabrous: Rough surface with short and stiff hairs-
e.g., Lantana, Leucas
6. Tomentose: Surface is completely covered with matted hairs-
e.g., Guazuma
53. 7. Glandular: Surface is covered with sticky and
glandular hairs, e.g., Jatropha glandulifera.
8. Gland dotted: Surface with a number of translucent
spots which become very clear when the lamina is
held against light-e.g., Citrus. Each spot represents
a place where oil is stored up. .
9. Srigose: Leaf surface bears sharp, stiff, straight and
often basally swollen hairs, all pointing in the same
direction.
10. Sericeous: Leaf surface with a silken sheen and
provided with silky hairs, e.g., gingelly.
54.
55. PHYLLOTAXY
• Phyllotaxy is the pattern of arrangement of leaves on stem and branches.
• The main purpose of phyllotaxy is to provide sufficient light to leaves.
• The form and arrangement of foliage leaves in buds is called
prefoliation,
• the form in which young leaves are folded or rolled on themselves in the
bud is called ptyxis,
• and the arrangeent of leaves within a bud is called vernation.
• There are two main kinds of phyllotaxy, namely radical phyllotaxy
and cauline phyllotaxy
• In the former, leaves are arranged in a cluster on a very short and stumpy
stem on the top of the root. e.g., radish.
• In cauline phyllotaxy, leaves are arranged on tem which has distinct
internodes.
• There are three main types of cauline phyllotaxy, alternate, opposite
and whorled.
56. (i) Alternate phyllotaxy
• This is the leaf arrangement in which leaves are arranged on
alternate nodes, with only a single leaf on each node.
• Leaf arrangement may be spiral, distichous, tristichous, or
pentastichous.
• In spiral phyllotaxy, alternate leaves are arranged spi rally
around the stem (e.g.. Hibiscus).
• In distichous phyllotaxy, alternate leaves are arranged in two
rows vertically on the two sides of the stem (e.g. Annona,
grasses)
• In tristichous phyllotaxy, leaves are arranged in three rows
(e.g., Cyperus),
• In pentastichous phyllotaxy, leaves are arranged in five rows
(e.g., Hibiscus).
57.
58. (ii) Opposite phyllotaxy
• Opposite phyllotaxy is the leaf arrangement in which a
pair of leaves are arranged oppositely on each node.
• Opposite phyllotaxy is of two kinds, namely decussate
and superposed.
• In decussate phyllotaxy, adjacent pairs of leaves are
arranged at right angles to each other (e.g. Ixora,
Calotropis Calotropis).
• In superposed phyllotaxy, adjacent pairs of leaves are
arranged exactly one above the other in the same
plane. (e.g. Quisqualis).
59.
60. (iii) Whorled phyllotaxy
• This is the leaf arrangement in which three or more
leaves arise from each node in the form of a whorl
or circle around the stem.
• e.g. Nerium (Oleander), Alstonia, Hamelia.
• Heterophylly is the occurrence of more than one
type leaf on the same plant.
• e.g. Limnophila heterophylla, Eucalyptus,
Broussoneita, jack tree, etc.
61.
62. Modifications of leaves
• Leaves are modified in different ways for
climbing, protection and nutrition.
• These modifications include :
• tendrils, hooks, spines, scale leaves, pitchers,
phyllodes, etc.
63. (i) Leaf tendrils
• These are long, spirally coiled and spring-like leaves.
• They help weak-stemmed plants to climb on a support.
• e.g. Pisum, Gloriosa, Lathyrus (sweet pea), Clematis.
• In Pisum, leaf tendrils are modified terminal leaflets,
• in Gloriosa they are modified leaf tips,
• in Lathyrus they are entire leaves,
• in Nepenthes they are modified petioles, and
• in Clematis they are modified rachillae.
• Leaf tendrils are sensitive to contact
64.
65. (ii) Leaf hooks
• Hook Leaf hooks are the hook-like modifications
of the terminal leaflets of the compound leaves
of some weak-stemmed plants for clinging and
climbing on a solid support.
• In Bignonia unguis cati, three terminal leaflets of
compound leaves are modified into cat-claw-like
hooks.
66.
67. (iii) Leaf spines
• Leaf spines are sharply pointed structures. They are
characteristic of xerophytic plants, such as cacti (e.g.
Opuntia, Ananas, Asparagus,etc).
• In Opuntia, they are formed from minute leaves of
axillary buds.
• In Ananas and Agave, they are modified leaf margins.
• In Opuntia, ordinary leaves are modified into scale
leaves, whereas the minute leaves of axillary buds
become spines.
• Scale leaves fall off in a short time.
• Leaf spines are modifications for defence, protection
and control of transpiration.
68.
69. (iv) Leaf scales
• Leaf scales are thin, stalkless and membranous
structures which protect the axillary buds located
in their axils.
• e.g. onion.
• In onion, they are fleshy due to the storage of
water, mucilage and food.
71. (v) Pitcher
• Pitcher is a flask-shaped modification of the leaf lamina for trapping insects.
• It is found in some insectivorous plants. e.g. Nepenthes,Sarracenia.
• In Nepenthes leaf lamina is modified into a pitcher.
• The mouth of the pitcher is covered by a lid, called operculum.
• It is a modified part of the leaf tip.
• The basal portion of the petiole is flat, leaf-like and photosynthetic.
• The upper portion is coiled like a tendril to hold the pitcher in vertical
position.
• The whole pitcher is a beautifully coloured to attract insects.
• A sugary secretion makes the rim of the mouth slippery.
• Insects, resting on the edge of the mouth, get accidentally slipped into the
pitcher.
• Soon, operculum closes the mouth to prevent their escape.
• The insects are digested by the enzymes secreted by the pitcher wall.
• The digested food is soon absorbed to the pitcher wall.
72.
73. (vi) Phyllode
• Phyllode is a flat, leaf-like and photosynthetic
modification of the petiole or rachis.
• It is a xerophytic adaptation to reduce transpiration.
• In this case, normal leaflets fall at an early stage.
• Then, petide or rachis develops to a phyllode.
• Phyllodes are common among Parkinsonia, Acacia, etc.
• In Acacia auriculiformis (Australian Acacia), leaflets are
altogether absent.
• But, in A.melanoxylon, they fall off at an early stage.
• In both the cases, rachis flattens out into a leaf-like
phyllode.
74.
75. Differences between phyllode and
phylloclade
Phyllode Phylloclade
(i) is a leaf modification (a
modification of petiole or rachis)
Is a stem modification
(ii) Usually unbranched Usually branched
(iii) Nodes and internodes absent Nodes and internodes present
(iv) Scale leaves absent Scale leaves present
(v) Axillary buds and spines absent Axillary buds are modified as spine
(vi) Never succulent Always succulent
76. Functions of leaves
(i) Manufacture of food by photosynthesis.
(ii) Gas exchange and transpiration through stomata.
(iii) Storage of food and water by fleshy leaves.
(iv) Vegetative propagation by adventitious leaf buds.
(v) Defence and protection by leaf spines.
(vi) Help in climbing by the formation leaf tendrils and
leaf hooks.
(vii) Food capture in insectivorous plants.
(viii) Help in pollination by attractive colouration.
