Page 120 - Ultimate Visual Dictionary (DK)

PLANTS

Liverworts and mosses A LEAFY LIVERWORT
Scapania undulata
“Stem”

LIVERWORTS AND MOSSES ARE SMALL, LOW-GROWING PLANTS that belong to the phylum
Bryophyta. Bryophytes do not have true stems, leaves, or roots (they are anchored to
the ground by rhizoids), nor do they have the vascular tissues (xylem and phloem)
that transport water and nutrients in higher plants. With no outer, waterproof “Leaf”
cuticle, bryophytes are susceptible to drying out, and most grow in moist habitats.
The bryophyte life-cycle has two stages. In stage one, the green plant (gametophyte)
produces male and female gametes (sex cells), which fuse to form a zygote. In stage
two, the zygote develops into a sporophyte that remains attached to the gametophyte.
The sporophyte produces spores, which are released and germinate into new green
plants. Liverworts (class Hepaticae) grow horizontally and may be thalloid (flat and Rhizoid
ribbonlike) or “leafy.” Mosses (class Musci) typically have an upright “stem” with
spirally arranged “leaves.”

Disk Disk Ray
Lobe (radial groove)
A THALLOID LIVERWORT Archegoniophore Lobe Lobe
Marchantia polymorpha (stalked structure Stalk
carrying archegonia) Stalk Disk
Gemma cup Thallus
(plant body) Stalk ARCHEGONIOPHORE
FROM BELOW
Gemma (detachable
tissue that produces
new plants)
Thallus Apical
(plant body) notch Rhizoid
Toothed margin SIDE VIEW OF
DETAIL OF GEMMA CUP of cup ARCHEGONIOPHORE
Pore
Thallus FEMALE
Gemma cup (plant body) GAMETOPHYTE
Ray
Midrib (radial groove)
Archegoniophore
(stalked structure MICROGRAPH OF LOBE
carrying archegonia)
MICROGRAPH OF THALLUS
Conocephalum conicum

Position
of air
chamber
Pore for
exchange
of gases

Upper
surface Rhizoid

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