Gametophores are always thin, at least along the edges. they may be shaped like a ribbon or a heart, or they may grow outward irregularly, forming a disk.
the upper surface in many is smooth, but in others thin, chlorophyllous lamellae grow upward.
internally, hornwort gametophytes have numerous chambers.
Gametangium development in hornworts is distinctive.
the chamber expands as the antheridia grow and finally its roof breaks; only then are antheridia exposed to the environment.
As sperm cells mature, sterile outer cells of antheridia transform their chloroplasts into chromoplasts, becoming orange or yellow.
after fertilization occurs, the zygote divides longitudinally; in mosses and liverworts, it divides transversely.
