Lycophytes and Pterophytes: The Ferns

Plants.

Th e bryophytes are the simplest of land plants. Th is group includes the mosses, liverworts,

and hornworts. Th e most recognizable of these are the mosses—there are

more than 1000 species of moss in North America alone! Th e peat mosses, of the

genus Sphagnum, may be the most numerous plants on ETh e bryophytes are the simplest of land plants. Th is group includes the mosses, liverworts,

and hornworts. Th e most recognizable of these are the mosses—there are

more than 1000 species of moss in North America alone! Th e peat mosses, of the

genus Sphagnum, may be the most numerous plants on Earth. In many ecosystems,

including Canada’s boreal forest, Sphagnum mosses can form a continuous ground

cover over hundreds and thousands of square kilometres (Figure 7).

Like the earliest of land plants, bryophytes have a protective cuticle and stomata

for gas exchange. Th ey do not have specialized vascular tissue or true leaves, roots, or

seeds. Most bryophytes are only a few centimetres in height.

Th e gametophyte generations of bryophytes produce swimming sperm in structures

called antheridia (singular: antheridium) and eggs (in structures called archegonia

(singular: archegonium). Bryophytes can therefore only live and reproduce in places

with at least occasional wet conditions, such as rains or heavy dew.

Th e green plants we recognize as mosses are the photosynthetic gametophyte individuals.

Aft er fertilization, the new, non-photosynthetic sporophyte individuals grow

out of the archegonia on the female gametophyte and get their nourishment from the

gametophyte. Th ese sporophytes seem to be part of the gametophyte but are actually

the off spring of the gametophyte plants. Th e sporophytes grow a tall stalk that bears a

structure called a sporangium (plural: sporangia), in which haploid spores are produced.

Th ese tiny spores are easily carried by winds and dispersed over a large area.

bryophyte a small seedless plant that

lacks vascular tissue

Figure 7 Various species of sphagnum

moss form a thick covering in this bog.

sporangium the structure in which

spores are produced

Figure 6 (a) Almost all plant surfaces produce a waterproof, waxy cuticle. (b) Stomata are small

openings in the epidermis that allow gas exchange with the air. Most leaves have thousands of

stomata per square centimetre.

cuticle epidermal cell

epidermis stoma

epidermal cell

C03-P23-OB11USB

SP

1st pass

Ontario Bio 11 U

0176504311

Pass

Approved

Not Approved

(a)

antheridium the specialized structure

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