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Nonvascular Plants: Mosses, Liverworts (Division Anthocerotophyta:…
Nonvascular Plants: Mosses, Liverworts
Concepts
plants traditionally divided into:
vascular cryptogams
2) vascular tissue but no seeds
clubmosses
ferns
scouring rushes
spermatophytes
both vascular tissue and seeds
cyads
gymnosperms
angiosperms
nonvascular plants
1) neither vascular tissue or seeds
liverworts
mosses
hornwots
Characteristics of Nonvascular Plants
embryophytes
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multicellular
surrounded by one/several layers of sterile cells
almost exclusively terrestrial
many have stomata
cuticle over much of their body
bodies=true parenchyma
gametangia
sporangia
no vascular tissue
hetermorphic generations
sportophyte & gametophyte differ structurally
Classification of Nonvascular Plants
3 distinct divisions:
Hepatophyta
liverworts
Anthocerotae
hornworts
Bryophyta
mosses
not known how closely related
differ in significant aspects
many features in common
Division Bryophyta: Mosses
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The Gametophyte Generation
ubiquitous
occuring in all parts of the world
in almost every environment
perennial
Water Transport
majority of mosses lack hydroids & leptoids
water conducted through capillary action
along exterior of stems
form narrow spaces
rhizoids
located base of stem
only anchor stem
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penetrate substrate surface
trichome-like structure
small/ multicellular
leaves/ stems very small
act as capillary channels
hydroids
innermost cortex cells
no cyctoplasm
end walls partially digested
conduct water/ dissolved minerals
elongated cells
leptoids
cells that resemble sieve cells
retain cytoplasm
elongate
lack nuclei
Development
begins when a spore germinates
sends out long, slender chlorophyllous cell
produces branched system of similar cells
protonema (plural, protonemata)
entire network
resembles filamentous green alga
distinguished by numerous small chloroplasts
undergoes mitosis
Morphology
gametophores
leafy stems
Reproduction
gametophore
produces gametangia
all mosses oogamous
large nonmotile egg cells
occur in megagametangia
called archegonia
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small biflagellate sperm cells
produced in microgametangia
called antheridia
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The Sporophyte Generation
zygote of moss
undergoes a transverse division
basal cell develops into
small bulbous tissue
called the foot
interface w/ gametophore
absorbs sugars, minerals, and water from gametophore
expansion into a simple apical sporangium
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upper cell grows by cell division
Metabolism and Ecology
two critical factors:
several mechanisms compensate
for inability of mosses to retain water
tolerant of desiccation
desiccated mosses resistant to high/ low temperature
and intense ultraviolet (UV) light
grow in permanently moist microhabitats
lack of conducting tissues
small size
Division Anthocerotophyta: Hornworts
The Gametophyte Generation
parenchymatous
succulent but brittle
winter annuals
after fertilization divides longitudinally
live less than 1 year
may be shaped like ribbon or heart
or grow irregularly forming a disk
The Sporophyte Generation
no seta
or discrete sporangium
foot embedded in gametophore
meristem just above the foot
produces new sporangium tissues
grow on moist soil
hidden by grasses/herbs
small inconspicuous thalloid plants
superficially resemble thalloid liverworts
Division Hepatophyta: Liverworts
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The Sporophyte Generation
most liverwort sporophytes:
calyptra-covered sporangium
elators
uncoil pushing spores out
single elongate cells
spring-shaped walls
foot
seta
clear thin walls
collapse quickly
extremely delicate
basic morphology like that of mosses
little variability exists
The Gametophyte Generation
Divided into two basic groups:
apical cell is established
growth of gametophore begins
archegoniophores
apex of radiating fingers
antheridiophore
umbrella-shaped outgrowth
male reproductive structure
bisexual
antheridia
archegonia
or unisexual depending on species
leafy liverworts
gametophore resembles moss
two rounded lobes
no midrib
thallose liverworts
body
aka thallus (plural, thalli)
air pores
cannot be closed
no guard cells
not stomata
or heart shaped/ bilaterally symmetrical
flat and ribbon like
small plants
some species greatly resemble mosses
Resemblance
More Resemblance
Multicellular
