Biology Today — December 2017

Classification of Gymnosperms

Gymnosperms

Cycadopsida

• Primitive group, containing
  plants with palm like habit
  and fern like foliage.


• Wood is manoxylic.


• Male cones are large
  with compactly arranged
  microsporophylls.


• Megasporophylls are loosely
  arranged and do not form a
  cone.


• Plants are mostly xerophytic.


• Examples : Cycas, Zamia, etc.

Coniferopsida

• Includes larger dominant
  gymnosperms.


• Monoecious.


• Stem branches are
  dimorphic, i.e., with long
  and dwarf shoots. Wood is
  pycnoxylic.


• Sporophylls form cones.


• Examples : Pinus, Ginkgo,
  Taxus.

Gnetopsida

• Includes advanced
  gymnosperms.


• Branches are dimorphic
  (long and dwarf shoots)
  as well as leaves are
  also dimorphic (scale
  and foliage leaves).


• Xylem shows vessels.


• Ovules are orthotropous.


• Examples : Gnetum,
  Ephedra, Welwitschia.

Ginkgopsida

• Represented by only one
  living member, Ginkgo
  biloba (living fossil).


• Dimorphic branches
  present.


• Leathery, fan shaped leaves
  having dichotomously
  branched veins present.


• Plants are dioecious.


• Male gametes
  multiflagellate and motile.

Economic Importance of Gymnosperms

Economic Importance

Resin

It is a semifluid secretion containing terpenes, resin, acids and esters which solidifies on

exposure to air. It helps in sealing, is antiseptic and toxic to pests, thus, prevents microbial

and insect attack. Resin is commercially extracted to obtain turpentine and rosin.

Ephedrine

It is a drug obtained from Ephedra

and used in curing respiratory ailment,

including asthma.

Paper

A wide range of gymnosperms are utilised in

manufacture of paper e.g., Picea, Pinus, Abies, etc.

Timber

The softwood of gymnosperms is used in preparation

of light furniture, plywood, packing cases, etc.

Food

Seeds of Pinus gerardiana are

edible and are eaten after roasting.

Affinities of Gymnosperms with Pteridophytes

• Usually perennial herbs or
  shrubs.


• Grow in moist, shady
  terrestrial places.


• Possess adventitious roots.


• Secondary growth found
  rarely or in very few
  pteridophytes.


• Ovules and seeds absent.


• Independent
  gametophytes.
  
  
  • Mostly trees.
  
  
  • Occur in xerophytic
    habitats.
  
  
  • Possess tap roots.
  
  
  • Secondary growth
    is of universal
    occurrence.
  
  
  • Presence of ovules
    and seeds.
  
  
  • Gametophytes
    dependent on
    sporophytes.
  
  
  
  


• Distinct alternation of generations with dominant
  sporophytic phase.


• Sporophytic plant body is differentiated into root,
  stem and leaves.


• Leaves show circinate vernation.


• Xylem lacks vessels (except for Gnetales).
  Phloem is devoid of companion cells.


• Several fossils and living pteridophytes show
  secondary growth like gymnosperms.


• Sporangia are formed on specialised leaves,
  known as sporophylls.

Pteridophytes Gymnosperms