Division Bryophyta
Liverworts, Hornworts and Mosses
I. Characteristics
A. Sporophyte has no direct connection with the ground, but is "parasitic"
on the gametophyte.
B. Gametophytes are always small - rarely over a few inches, and are
photosynthetic.
C. Although bryophytes are land plants, they are still dependent upon
water for fertilization, as the sperm swim in a water film.
D. Because of their small size, they do not need, or have specialized
conduction systems.
E. The diploid sporophyte usually consists of a basal foot,
an elevating seta and a terminal sporangium - the capsule.
Spores are produced as a direct result of meiosis.
F. True roots, stems and leaves lacking. Consists rather of rhizoids,
caulalia,
& phyllidia.
G. Gametophytes homothallic or heterothallic.
II. General life history
Archegonia flask-shaped with venter, neck, ventral
canal cell, neck canal cells and cover cells. Egg in venter. At maturity,
the last 3 structures disintegrate, opening the neck for the entrance of
the sperm. Antheridia consist of rounded structure consisting of a single
layered jacket surrounding a central mass of cells - androcytes.
Each changes into slender biflagellated sperm.
The sperm are released when the antheridium ruptures,
thus allowing them to swim freely in a water film. After fertilization,
many divisions form a multicellular embryo which is nourished by the gametophyte.
The embryo grows & forms a mature sporophyte, within which sporogenous
tissue will form spore tetrads, which in turn are released as the spores,
forming either the gametophyte, or the protonema, which in turn forms the
typical gametophyte.
III. Class Hepatacae - Liverworts
Dorsiventral plants - green thallus - often ribbon-like.
Branch dichotomously.
X-S of thallus shows many air chambers opening through a pore, lined
with photosynthetic cells.
Rhizoids function as roots.
Most liverworts grow where there is considerable moisture.
A. Riccia
Widely distributed form, needing water for growth,
but resisting drought successfully. Some forms aquatic, growing on water.
1. Gametophyte
Gametangia located in furrows on upper surface of
thallus. Homothallic.
a. Antheridium - sterile jacket surrounding many sperm. Sperm
leave antheridium only when moisture is present for them to swim in.
b. Archegonium - Flask shaped with venter, neck & cover
cells. Attached by short stalk. At maturity, cover cells spread, neck canal
cells dissolve. Sperm swim towards egg, drawn by a chemical attractant.
2. Sporophyte.
Diploid zygote forms multicellular embryo in venter.
a. Sporangium - Outer layer - sterile jacket, inside is sporogenous
tissue which forms spore mother cells. Meiosis - spore tetrad - mature
spores. Spores released only when gametophyte dies and decays.
B. Marchantia.
Forms large mats on soil or rocks in moist shady
environs.
1. Gametophyte.
Differs from Riccia in that gametangia are
raised above the surface of the thallus.
a. Asexual reproduction
i. Fragmentation
ii. Gemmae cups & gemmae or gemmules
Small discs of green tissue. Gemmae germinate directly
into new gametophytes.
b. Sexual reproduction
Actual gametangia are very similar to those of Riccia.
However Marchantia is heterothallic, with the antheridia on antheridiophores
& archegonia on archegoniophores. Antheridiophores are disc
like, with scalloped edges. Antheridia are deep in the upper portion. Archegoniophores
with 8 lobe-like fingers, under which are located the archegonia.
2. Sporophyte
Zygote forms embryo, which differentiates into a
foot, seta, & sporangium. Archegonium grown at same pace as sporangium,
forming a calyptra. Sporogenous tissues forms spore mother cells
& spores. Elaters eject spores.
IV. Anthocerotae. - Hornworts, Anthoceros
A. Gametophytes simple, gametangia not surrounded by jacket of sterile
cells. Homothallic or heterothallic.
B. Sporophyte notable in that it has meristematic tissue.
V. Class Musci. - Mosses
Small, but conspicuous plants. Grow on banks, rocks
in streams. Can resist drought, but require moisture for growth. Most forms
exhibit 2 growth habits. 1. the creeping filamentous stage - protonema,
and 2. the moss plant - upright. The protonema may give rise to many moss
plants. Mature sporophyte has typical foot, seta & capsule, but capsule
is somewhat more complex than Hepatophytes.
A. Gametophyte
Protonema is first stage, followed by the leafy
gametophyte with its rhizoids, caulalia & phyllidia. X-S of caulalia
shows a central cylinder, a cortex and an epidermis.
1. Sexual reproduction.
Many mosses are monoecious - Male and female
in same plant. Others are dioecious. Ex. - Mnium & Polytrichium.
Antheridia
of mosses are essentially the same as in liverworts. Archegonia differ
in having a longer neck and longer stalk to the archegonium.
B. Sporophyte
Following fertilization, the embryo begins to form,
with the foot penetrating into the venter and even to the apex of the leafy
gametophyte. It absorbs water & nourishment from the gametophyte for
the sporophyte. As the seta elongates, the old archegonium is torn from
the gametophyte and remains on the capsule as the calyptra. Sporogenous
tissue forms around the columella, and spore mother cells undergo
meiosis to form tetrads of haploid spores. At the top of the capsule is
the cap-like operculum beneath which is a double row of triangular
peristome
teeth. The teeth are attached to a thick-walled annulus around
the upper end of the sporangium. When the sporangium is mature, the operculum
breaks off, and the peristome is left holding the spores in place. The
teeth are very sensitive to humidity (I.e. hygroscopic) and when
wet or very humid weather occurs, they bend into the capsule, when dry,
they straighten out and lift some spores out with them. The spores are
then distributed by air currents, and later they germinate into protonemae.
To Top of Page 
To Plant Diversity Page 
To Tony Futcher's Home Page