Biology Today - May 2018

• Embryo stage is present. The embryo grows into a sporophyte.


• The sporophyte consists of foot, seta and capsule.


• Sporophyte produces haploid meiospores inside its capsule.


• Each spore on germination produces a gametophyte, either directly or a juvenile filamentous stage celled protonema.


• Bryophytes show heteromorphic or heterologous alternation of generations.

Table : Characteristics of different classes of bryophytes

Features Hepaticopsida Anthocerotopsida Bryopsida

Common name Liverworts Hornworts Mosses

Gametophytic plant

body

May be thallose or foliose,

Unicellular rhizoids.

Thallose,

aseptate rhizoids

Gametophyte has two growth stages: thalloid

protonema stage and leafy gametophore

stage. Obliquely septate rhizoids.

Sex organs Present on dorsal surface of

thallus.

Present on dorsal

surface of thallus.

Develop from the superficial cells at the apex of

leafy gametophore.

Sporophyte

or sporogonium

Simple, represented by

capsule only e.g., Riccia

or differentiated into foot,

seta and capsule (e.g.,

Marchantia).

Differentiated into a

bulbous foot, small

meristematic seta and

long cylindrical capsule.

Differentiated into foot, seta and capsule.

Elaters Generally present, absent in

some like Riccia.

Pseudoelaters are

present in the capsule.

Absent

Sporogenous cells Develops from endothecium. Develops from

amphithecium and

endothecium, forms

sterile columella.

Develops from outer layer of endothecium,

inner layer forms sterile columella.

Dehiscence of capsule Irregular and indefinite Irregular Regular

Examples Riccia, Marchantia,

Sphaerocarpos, etc.

Anthoceros, Notothylus,

Megaceros, etc.

Sphagnum, Polytrichum, Funaria, etc.

Economic Importance of Bryophytes

• Bryophytes such as mosses prevent soil erosion by forming dense mats over the soil surface.


• Dry Sphagnum can keep seedlings and cut plants moist during transportation and propagation as it can absorb 18-26 times its
  weight of water.


• Mosses alongwith lichens play a very important role in the formation of soil over the bare rocky surface.


• Some bryophytes have important medicinal uses. For example, the tea prepared from Polytrichum commune is used to dissolve
  stones of kidney and gall bladder.
  Bryophytes seldom attain great heights and thus remain small in size. It may be due to absence of roots and vascular tissues,
  absence of cuticle on plant body, absence of mechanical tissues and requirement of external sheet of water for capillary conduction.

PTERIDOPHYTES

• Pteridophytes are seedless vascular plants that have sporophytic plant body and inconspicuous gametophytes.


• The sporophyte is differentiated into true roots, stem and leaves.


• All the vegetative parts possess vascular tissues (xylem and phloem) organised in definite groups or steles.


• The sporophyte reproduces asexually by means of spores, produced in small capsules called sporangia.


• Leaves bearing sporangia are called sporophylls which may be widely scattered or clustered in definite areas and structures called
  cones or strobili.


• The diploid spore mother cells or sporocytes within the sporangia undergo meiosis to form haploid spores.


• The spores produced are of only one type in homosporous pteridophytes (e.g., Lycopodium, Pteridium) or of two types (smaller
  microspores and larger megaspore) in heterosporous pteridophytes (e.g., Selaginella, Marsilea).