Bryophytes

Gametophyte (gamete-producing) phase

• Green, photosynthetic, multicellular, and macroscopic

• Usually a few centimeters in size; found on forest floors, bark, rocks, and leaves 

• The gametophyte is the dominant and persistent phase

• It is independent, with a system for making food and absorbing nutrients

• Many bryophytes are poikilohydric (poikílos means “variable,” and hydro refers to “moisture”), in which they can quickly take in and lose water and have little means to control it. 

  • As an adaptation, the plants can survive drying out until their cells are entirely devoid of water.

  • When moisture returns, they quickly rehydrate, and their metabolism returns to normal (Proctor & Tuba, 2002).

Stems

• Lack true vascular tissue, such as xylem or phloem

• May have water-conducting cells called hydroids, which lack lignified thickenings on the cell wall

• Some also have sugar-conducting cells called leptoids, which are similar to phloem

Leaves

• Some bryophytes are leafy (i.e., all mosses, some liverworts), and others are thalloid (i.e., some liverworts, all hornworts)

Roots

• Most have rhizoids (root-like structures) for anchoring the plant to a substrate, and they have some capacity to absorb water and minerals

Reproduction

• Bryophytes produce archegonia (with an egg) and antheridia (with sperm) 

• Sperm need to swim on a film of water to reach and fertilize the egg.

• Monoicious: male and female gametangia on the same individual

• Dioicious: gametangia on separate individuals, creating male and female plants

Sporophyte (spore-producing) phase

• Sporophyte is comprised of 1) a stalk, called the seta, with 2) a spore case at the end called the theca

  • This feature is found in the mosses and liverworts, but the hornworts lack a seta

• The sporophyte is multicellular and macroscopic, but not photosynthetic

• The sporophyte stalk/seta does not branch, resulting in a single sporangium per sporophyte ("uni-sporangiophyte")

• The sporophytes are usually a few centimeters in height, found growing off the gametophyte

• Sporophyte is epiphytic and dependent on the gametophyte for nutrition. 

Foot

• The foot is a basal bulbous zone on the sporophyte

• This structure facilitates the transfer of nutrients from the parent gametophyte to the sporophyte