Theory:

These are the primitive and simplest plants that are non-vascular (xylem and phloem are absent in them) and seedless. Hence, they are known as vascular cryptogams. These plants live on land and in water, as water is essential for them to complete their life cycle. Hence, they are known as amphibians of the plant kingdom.
 
Bryophytes.jpg
Some of the bryophytes
Life cycle of bryophytes:
These are organisms that have a distinct alternation of generations. The gametophytic generation of these organisms is dominant, and the sporophytic generation is small. Due to this, the sporophytic age depends on the gametophytic generation.
 
Gametophytic generation:
  
The gametophytic generation is a dominant one as, during this phase, the plant contains photosynthetic leaf-like structures, thallus, stem, and rhizoid. The root-like rhizoid is a structure by which the plant remains fixed to the substratum. During the gametophytic generation, the plant can be either thalloid (liverworts) or leafy (mosses).
 
Sporophytic generation:
 
This generation of the bryophytes is barely noticeable. It appears for only a short period.
Reproduction in bryophytes:
The bryophytes undergo a sexual mode of reproduction which is of oogamous type. These plants have well-developed sex organs known as antheridia and the archegonia, which are the male and female sex organs respectively.
  • The archegonium contains an egg.
  • The antheridium produces antherozoid (male gamete) that swims with water and reaches the archegonium.
  • The antherozoid fertilizes the egg and forms a diploid zygote (2n).
  • The zygote is the first cell that develops into sporophytic generation and produces haploid spore (n) by meiosis.
  • Hence, spores are the first cells of the gametophytic generation.
Moss_alternation_of_generations_03-2012.png
The life cycle of bryophytes
Reference:
https://upload.wikimedia.org/wikipedia/commons/8/89/Mousse_Bryophytes._Mahieddine_Boumendjel.jpg
https://upload.wikimedia.org/wikipedia/commons/d/d7/2018-01-12_%28108%29_Unidentified_Bryophytes_%28moss%29_in_a_garden_at_Haltgraben%2C_Frankenfels.jpg
https://pixabay.com/photos/moss-bryophytes-rokytnik-hylocomium-1466979/
https://upload.wikimedia.org/wikipedia/commons/e/ea/Moss_alternation_of_generations_03-2012.png