Final answer:
Bryophytes are nonvascular plants originating around 450 million years ago; they reproduce via spores that require moist environments. They lack lignin and true tracheids and survive in various climates including damp habitats and the tundra.
Step-by-step explanation:
Definition of Bryophytes
Bryophytes are a group of nonvascular plants that are considered the closest extant relatives of early terrestrial plants, appearing first in the Ordovician period, about 450 million years ago. The spores of bryophytes are protected by sporopollenin, which contributes to their resilience and is key to their reproduction. Unlike vascular plants, bryophytes lack lignin and true tracheids for water conduction, relying instead on specialized conducting cells and external moist conditions to fertilize through swimming sperm.
Noteworthy habitats for bryophytes include damp locales and inhospitable environments like the tundra, where they can withstand desiccation. Bryophytes' life cycles feature alternation of generations, wherewith meiosis in the sporophyte generation, haploid spores are produced, leading to a new generation of gametophytes.
There are approximately 18,000-25,000 species of bryophytes encompassing three phyla: the liverworts or Marchantiophyta, the hornworts or Anthocerotophyta, and the mosses or true Bryophyta, each thriving in different climates but often associated with moist environments.