nonvascular

Nonvascular plants, commonly referred to as bryophytes, are a group of land plants that lack vascular tissue (xylem and phloem). The informal grouping includes three divisions: mosses (Bryophyta), liverworts (Hepatophyta), and hornworts (Anthocerotophyta). They are generally small and ground-hugging, occurring in moist, shaded environments where water is readily available for physiological processes and reproduction. Unlike many vascular plants, nonvascular plants rely on diffusion and osmosis for internal transport.

Anatomy and life cycle: Nonvascular plants do not have true roots, stems, or leaves. They typically possess simple anchoring structures called rhizoids and a thallus or leafy gametophyte that carries out photosynthesis. The life cycle is characterized by alternation of generations, with the dominant, photosynthetic haploid gametophyte providing most of the visible plant body. The diploid sporophyte is usually smaller, often dependent on the gametophyte, and produces spores within sporangia. For fertilization, water is required for the motile sperm to swim from an antheridium to an archegonium.

Habitat and ecology: They inhabit a range of moist microhabitats, including soil, rocks, tree bark, and leaf litter. They play roles in soil formation, moisture retention, and colonization of bare surfaces. They are typically among the first organisms to inhabit new or disrupted environments and can survive periods of desiccation.

Taxonomy and evolution: Bryophytes are divided into three divisions—Bryophyta (mosses), Hepatophyta (liverworts), and Anthocerotophyta (hornworts). They are among the earliest land plants and provide insight into the early evolution of embryophytes, though as a group they form a grade rather than a single clade within green plants.