Hornworts

This group gathers Mosses and Liverworts subcategory members belonging to the division Anthocerotophyta, the hornworts, the smallest of the three major bryophyte lineages by number of described species and, alongside the liverworts and true mosses, one of the three earliest-diverging branches of land plant evolution. A hornwort's flattened, lobed thallus superficially resembles that of a thalloid liverwort, but its long, slender, horn-shaped spore-producing structure, which gives the group its common name, grows continuously from a basal region for as long as growing conditions remain favorable, unlike the single, short-lived capsule a moss or liverwort produces. Several hornwort species host a symbiotic, nitrogen-fixing cyanobacterium within internal cavities in the thallus, a partnership that lets the plant thrive in nitrogen-poor soils where many other small plants would struggle, and hornworts are also notable among land plants for chloroplasts containing a single large pyrenoid, a structure more typically associated with algae than with any other land plant lineage.