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Chapter 21: Nonvascular Plants: Mosses, Liverworts, and Hornworts - Coggle…
Chapter 21: Nonvascular Plants: Mosses, Liverworts, and Hornworts
Concepts
plants traditionally divided into 3 categories
plants without vascular tissues or seeds (nonvascular plants)
arose first
mosses
liverworts
hornworts
vascular cryptograms
clubmosses
scouring rushes
ferns
those with both vascular tissue and seeds (spermatophytes)
cycads
conifers
angiosperms
Characteristics of Nonvascular Plants
technically embryophytes
no vascular tissue
have multicellular
sporanigia
gametangia
surrounded by one or several layers of sterile cells
body composed of true parenchyma
derived by 3-D growth
almost exclusively terrestrial
have cuticle over much of their bodies
many have stomata
Classification of Nonvascular Plants
not known how closely related they are
many features in common but differ in significant aspects
3 distinct divisions
liverworts (Hepatophyta)
mosses (Bryophyta)
hornworts (Anthocerotophyta)
Division Bryophyta: Mosses
The Gametophyte Generation
mosses are ubiquitous
occur in all parts of the world
in almost every environment
perennial
morphology
gametophores
leafy stems
grow close together
leaves of mosses did not not evolve from same structures as vascular leaves/stems did
water transport
hydroids
innermost cortex cells
conduct water/dissolved minerals
elongated cells
lose cytoplasm when mature
end walls are primarily digested
leptoids
cells that resemble sieve cells
elongate
prominent interconnections with adjacent cells
lack nuclei at maturity
retain their cytoplasm
majority of mosses lack hydroids and leptoids
water conducted long exterior of their stems by capillary action
leaves stems small
form capillary channels
transport water
rhizoids
base of stem
small, multicellular
trichome like structures
penetrate surface of substrate
don't absorb water/minerals
lack chloroplasts
reddish walls
only anchor the stem
development
growth of gametophyte begins when spore germinates
send out a long, slender chlorophyllous cell
this cell undergoes mitosis and produces branched system of similar cells
entire network is a protonema
resembles filamentous green algae
distinguished by numerous chloroplasts in each cell
reproduction
gametophore produces gametangia
mosses are oogamous
small biflagellate sperm cells
produced in microgametangia
antheridia
short stalk
outermost layer of sterile cells
inner mass of cells differentiate into sperm cells
large nonmotile egg cells
occur in megagametangia
archegonia
vase shaped w long neck
neck hollow at maturity
single egg located at the base
The Sporophyte Generation
zygote of moss undergoes transverse dissection
basal cell develops into small bulbous tissue
the foot
interface with gametophore
absorbs
sugars
minerals
water
upper cell grows by cell division and expansion into simple apical sporangium
called the capsule
consists of outer layer of sterile cells
inner column of sterile cells (the columella)
seta
between foot and sporangium
narrow stalk
operculum
apex of sporangium
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Metabolism and Ecology
two critical factors in metabolism/ecology of mosses
small size
lack of conducting tissues
mechanisms to compensate for lack of ability to retain water
permanently moist microhabitats
rainforests
spray zones (waterfalls)
cloud forests
tolerance of desiccation
drying does not harm them
only have to retain 30% of their weight in water to live (dormant)
remarkably resistant to high/low temps
resistance to uv light
Division Hepatophyta: Liverworts
small plants
some species are leafy and greatly resemble mosses
The Gametophyte Generation
divided into 2 basic groups
leafy liverworts
gametopore greatly resembles that of a moss
typically have two rounded lobes
no mid rib or conducting tissue
thallose liverworts
flat and ribbonlike
or heart shaped/ bilaterally symmetrical
thallus
refers to the body
stratified
tend to be thicker than those of leafy liverworts and mosses
air pores
not stomata
no guard cells
cannot be closed
liverwort gametophores
may be bisexual
produces both
antheridia
archegonia
can be unisexual (depends on species)
antheridiophore (male structure)
umbrella-shaped outgrowth
archegoniophores (female)
apex is set of radiating fingers
The Sporophyte Generation
little variability exists in sporophytes of most liverworts
basic morphology is like that of mosses
most liverwort sporophytes have
foot
seta
extremely delicate
composed of thin, clear-walled cells
collapse quickly
calyptra-covered sporangium
elators
single, elongate cells
spring-shaped walls
Division Anthocerotophyta: Hornworts
small inconspicuous thalloid plants
grow on most soil
hidden by grasses and other herbs
superficially resemble thalloid liverworts
gametophores being ribbon-shaped and thin
no distinct stem or leaves
The Gametophyte Generation
gametophores
always thin (along edges)
become more than 4-5 cells thick only in center
may be shaped like ribbon or heart
may grow outward irregularly, forming a disk
parenchymatous
succulent but brittle
does not tolerate drying
typically live for less than 1 year in temperate climates
act as winter annuals
The Sporophyte Generation
hornworts have foot embedded in gametophore tissue
just above foot is meristem
continually produces new sporangium tissue
replaced by cells of basal meristem
no seta
no discrete sporangium