Chapter 16: Bryophytes

Bryophytes are small, nonvascular plants distributed across diverse habitats including tropical forests, wetlands, arctic regions, deserts, and even Antarctic ecosystems. Lacking lignified vascular tissues, they absorb water and nutrients directly through their leaf and stem surfaces, depending on ambient moisture and specialized cellular structures such as hyaline cells in mosses. These plants play critical ecological roles by sequestering substantial amounts of carbon through Sphagnum peat accumulation, stabilizing soil substrates, pioneering colonization of barren surfaces, and functioning as bioindicators of atmospheric pollution. The chapter traces bryophyte evolutionary relationships to charophycean algae and vascular plants, identifying shared characteristics including multicellular gametangia with protective envelopes, matrotrophic embryos retained within archegonia, multicellular diploid sporophytes, spores enclosed in sporopollenin walls, and apical meristems. Bryophytes diverge fundamentally in their gametophyte dominance and reduced, nutritionally dependent sporophytes. The reproductive mechanisms require water for flagellated sperm dispersal to eggs, and successful fertilization produces embryos nourished maternally through placental transfer cell interfaces. Spores ensure colonization and desiccation survival. The three major bryophyte divisions display distinct morphologies and life strategies: liverworts exceed 5200 species with thalloid or leafy gametophytes and specialized gametophores for sexual reproduction, demonstrated by Marchantia's antheridiophores and archegoniophores alongside vegetative reproduction through gemma cups; mosses comprising approximately 12800 species include Sphagnum in peatlands dominating global carbon dynamics, Andreaea splitting capsules for spore discharge, and true mosses with peristome teeth regulating spore release and specialized conducting tissues including hydroids and leptoids; hornworts represent roughly 300 species characterized by rosette gametophytes, unicellular rhizoids, basal sporophyte meristems, permanent stomata, and frequent nitrogen-fixing cyanobacterial symbiosis. Together these taxa illuminate fundamental plant adaptations to terrestrial existence including desiccation tolerance, nutritional acquisition from soil and atmospheric sources, and water-dependent sexual reproduction mechanisms.