Biology Today — January 2018

Procumbent
Branches flat on ground,
e.g., Tribulus.

Diffused

Branches spread in all directions,

e.g., Boerhaavia.

Decumbent

Some branches are partially vertical,

e.g., Tridax.

Types of Aerial Stem

Reduced

• Stem is reduced to small disc.


• Nodes and internodes are not distinguishable.


• They are modified as per the need of plants,
  such as


• Reduced green discoid stem is present above
  the base of root, with leaves crowded together
  on it (radical leaves), e.g., carrot, turnip, etc.


• Reduced discoid stem may be green and
  flattened to float on water surface, e.g., Wolffia,
  Lemna.

Erect

• Common type of aerial stem. Sufficiently strong to remain erect or upright
  without any external support, e.g., maize, mango.
  Culms
  Erect stems with swollen nodes or jointed stems, e.g., bamboo.
  Caudex
  It is unbranched erect stem.
  Branched
  Branched erect stems may be either excurrent or deliquescent.

Root climbers

Stem clings to the support

by adventitious roots, e.g.,

ivy, betel.

Tendril climbers

Green thread like sensitive structures called

tendrils that coil around support and help weak

shoots to climb up, e.g., Passiflora, Antigonon.

Scramblers

Stems are able to rise up a support by clinging

to it with the help of curved thorns, e.g.,

Bougainvillea, leaflet hooks, e.g., Doxantha, etc.

Lianas

Woody twiners

or climbers, e.g.,

Phanera vahlii.

Weak

• Such stems are thin, soft and cannot stand erect, therefore, require a
  support.


• These stems are broadly of two types.

Prostrate (sub-aerial)

Weak stem, require support of ground for spreading and proper exposure of leaves and reproductive organs.

Upright

Twiners

• Long, slender, flexible and sensitive stem. Coils around
  an upright support like a rope, e.g., Lablab, Ipomoea.

Climbers

• Weak and flexible stem that are unable to coil around an upright
  support by itself, but requires certain clasping structures.

Trailers

• The shoots trail or spread horizontally
  along the ground without rooting at
  intervals, e.g., Convolvulus, Euphorbia.

Creepers

• The shoots spread along the ground and root at intervals. They also help in vegetative propagation.

Offset

• One internode long, small runners
  usually found in rosette plants at the
  ground or water level. E.g., Eichhornia.

Lamina

Swollen

petiole

Spongy

stem

Offset

Root

pocket

Fig.:Offset ofEichhornia

Stolon

• Horizontal or arched runner which can
  cross over small obstacles.


• Each stolen has one or more nodes possessing
  scale leaves and axillary buds.


• It possesses comparatively longer
  internodes. E.g., Fragaria.

New shoot

Scale leaf

Stolon (runner)

Adventitious root

Fig.:Stolon ofFragaria

Runners

• Develops at the base of erect shoot
  called crown and grows horizontally on
  the surface of soil.


• Each runner has one or more nodes which
  bear scale leaves and axillary buds.
  E.g., Cynodon dactylon

Green leaf

Scale leaf

Node

Runner Fibrous

adventitious roots

Fig.:Runner of grass