Biology Today — January 2018

Types of Leaf

Possess a single or undivided lamina

with smooth or incised margins but

the marginal incisions are not deep

up to midrib or petiole.

Possesses lamina divided into a

number of leaflets with incisions

deep upto midrib or petiole.

Palmate simple

leaf

• The incisions are
  pointed towards
  the petiole, e.g.,
  Ricinus.

Fig.: Palmate simple

leaf of Ricinus

Palmate compound leaf

• The incisions are pointed towards the base and are connected to the petiole tip. Depending
  upon the number of leaflets present, it can be
  (i) Unifoliolate - Single leaflet separated from petiole e.g., Citrus, etc.
  (ii) Bifoliolate - Two leaflets attached side by side at the tip of petiole, e.g., Bignonia, etc.
  (iii) Trifoliolate - Three leaflets e.g., Aegle, Butea, etc.
  (iv) Quadrifoliolate - Four leaflets attached to tip of petiole, e.g., Marsilea, etc.
  (v) Multifoliolate - Five or more leaflets present at the tip of petiole, e.g., Gynandropsis, Bombax, etc.

Leaf

Articulation

Winged petiole

Fig.: Unifoliolate compound leaf of Citrus

Pinnate compound leaf

• The incisions are pointed towards rachis (midrib) and leaflets
  are present laterally in opposite manner. Pinnate compound
  leaves are of various kinds:
  (i) Unipinnate - Leaf divided only once in a pinnate fashion. It can be:
  
  
  • Paripinnate Cassia, Cicer, etc.
  
  
  • Imparipinnate e.g., rose, Azadirachta, etc.
    (ii) Bipinnate - Pinnate leaf is divided twice pinnately, e.g., Mimosa,
    Acacia, etc.
    (iii) Tripinnate - Leaf is thrice pinnate, e.g., Moringa, Melia etc.
    (iv) Decompound - Leaf is more than thrice pinnate, e.g.,
    Coriandrum, Daucus, etc.
  
  
  
  

RachisRachis

Petiole

Fig.: Decompound

leaf of Daucus

Pinnate simple

leaf

• The incisions
  point towards
  the midrib, e.g.,
  Raphanus.

Fig.: Pinnate simple leaf

of Raphanus sativus

Types of Leaf

(Depending upon the

incision of lamina)

Simple leaf

Compound leaf

Modications of Leaf

Modications of Leaf

Leaf spines

Leaf gets modified into spine

in order to protect the plant from

grazing animals as well as reduce

the rate of transpiration, e.g.,

Berberis, Acacia.

Leaf

spines

Stem

Fig.: Leaf spines of barberry

Leaf tendrils

Tendrils are wire-like sensitive structures that help the

plants in climbing by coiling around a support. These

can be whole leaf tendrils, e.g., Lathyrus aphaca

(wild pea); leaflet tendrils, e.g., Lathyrus odoratus

(sweet pea); petiolar tendrils, e.g., Tropaeolum majus

(garden nasturtium); rachis and petiolule tendrils,

e.g., Clematis ; rachis tip tendrils, e.g., Lens culinaris

(lentil); leaf tip tendrils, e.g., Gloriosa superba (Glory

lily) and stipular tendrils, e.g., Smilax.

Whole

leaf

tendril

Stipule

Fig.: Whole leaf tendril

of Lathyrus aphaca

Phyllodes

Phyllodes are flat, green

coloured, photosynthetic leaf-like

modifications of petiole and rachis,

e.g., Australian Acacia (Acacia

auriculiformis), Parkinsonia, etc.

Stem

Phyllode

Leaflet

Fig.: Phyllode of Acacia

Leaf pitcher

In some insectivorous plants, the leaves

or their parts are modified to form a large

pitcher that is a special insect catching

organ. They catch and digest insects to

fulfill their nitrogen requirements, e.g.,

Nepenthes, Dischidia, etc.

Pitcher

Tendril petiole

Lid

Fig.: Leaf pitcher of

Nepenthes

Succulent leaves

Succulent leaves occur in plants of

saline and xerophytic habitats, e.g.,

Aloe, Agave, Bryophyllum.

Fig.: Succulent

leaves of Aloe

Leaflet hooks

The terminal leaflets of the compound

leaves become transformed into three

stiff claw-like and curved hooks.

Leaflet hooks help the plant in

climbing, e.g., Doxantha unguis-cati.

Leaflet

hooks

Fig.: Leaflet hooks of

Doxantha unguis-cati

Fig.: Leaf bladder of

Utricularia

Dissected

bladderLeaf leaf

Spongy

horizontal stem

Leaf bladder

In insectivorous hydrophytes like

Utricularia, leaf is profusely dissected

and some parts of it are modified

into bladder-like structures which

help in catching water insects.