KINGDOM PLANTAE: General characteristics and Bryophytes
Characteristics: This suite of characters are common to all members of the Plant Kingdom. Certain of
these characters are found among various algal groups, but no single species of algae has this entire set
of characters.
1) Plants with chlorophyll a & b, carotenoids
2) Starch stored within chloroplasts
3) Cellulose primary component of cell walls
4) Plants form phragmoplasts and a cell plate during cell division
5) Sporic life cycle: Traditional view was that ancestors had well-developed alternation of
heteromorphic generations; current view is that it is more likely that the sporic life cycle of
bryophytes was derived from a zygotic life cycle
6) Oogamous
7) All plants have embryos - zygotes divide within and supplied with nutrients from gametophyte
generation
8) Movement onto dry land facilitated by development of protective layer of sterile cells around sperm
and egg-producing cells of male and female gametangia - antheridia and archegonia, respectively as well as around the sporangia
8A) development of cuticle and stomata
BYRYOPHYTES: LIVERWORTS (DIV. HEPATOPHYTA), HORNWORTS (DIV.
ANTHOCEROPHYTA) and MOSSES (DIV. BRYOPHYTA)
CHARACTERISTICS COMMON TO ALL BRYOPHYTES:
- Gametophytes nutritionally independent of sporophytes, but sporophytes attached to and, for the most
part, nutritionally dependent upon gametophytes
- Gametophyte dominant generation in bryophytes (vs vascular plants where sporophyte is dominant
and conspicuous).
- Rhizoids anchor the gametophyte to the substrate; not a vascular tissue so does not conduct water.
- Sperm swim through water to reach egg located inside an archegonium
CHARS./TAXA
RHIZOIDS
STOMATA
CONDUCTING CELLS
HEPATOPHYTA
YES (unicellular/absent)
NO
NO
ANTHOCEROPHYTA
YES (unicellular)
YES
NO
I. Division HEPATOPHYTA: LIVERWORTS - Thallose and leafy forms
(ca. 300 genera; 6000-10,000 spp.)
BRYOPHYTA
YES (multicellular)
YES
YES [but not always]
- Earliest fossils from Devonian
- Mostly found in wet (aquatic, semi-aquatic or moist terrrestial) habitats
NOTABLE GENERA: Riccia, Ricciocarpus, Marchantia, Conocephalum, Porella
LIFE CYCLE:
- Haploid gametophytes develop directly from spores, in most cases - (i.e., no protonema)
- gametophytes can be monoecious or dioecious
- in monoecious species (spp., henceforth), gametophores (archegoniophores &
antheridiophores: specialized branches bearing gametangia) develop on one gametophyte
- in dioecious spp., female gametophyte develops archegoniophores containing archegonia
which hold one egg and male gametophytes develop stalked antheridiophores which contain
antheridia which produce biflagellate sperm; antheridia are contained slightly below the
upper surface of the antheridiophore; sperm have been shown to be dispersed by raindrops
for a distance of 60 cm.
- archegonia are flasklike in shape with a long neck and a swollen basal portion, the venter.
The central cells of the neck, the neck canal cells, disintegrate at maturity. In the venter are
the egg, and the ventral canal cell. The latter also disintegrates when the archegonia reaches
maturity. The ventral canal cell and neck canal cells are extruded as slime through which
the sperm swim. Fertilization of the eggs of the first formed archegonia happens before the
stalk of the archegoniophore begins to elongate.
- zygote divides and develops into an embryo within archegonia
- embryo differentiates into young sporophyte and sporogenous tissue (2n) within the enlarged
archegonium (= calyptra); in some taxa, the sporophyte differentiates into three separate
regions: the enlarged foot, the seta or stalk and the capsule or sporangium. Foot forms a
connection between gametophyte and sporophyte and facilitates the transport of nutrients
from gametophyte to developing sporophyte. Sporophytes are photosynthetic at maturity.
- sporogenous tissue (sporocytes or spore mother cells) undergoes meiosis to produce
spores (1n) (meiospores because they are formed via meiosis) within mature
sporophyte
- calyptra degrades and spores disperse from sporophytes within archegonial heads
- spores germinate and develop into gametophytes
- ASEXUAL REPRODUCTION through gemma cups - production of multicellular gemmae that
produce gametophytes
- GROWTH: localized at apex w/ one prominent apical cell.
- gametophytes develop directly from spores, but some form a filament of cells first.
- thallose or flat, dorsiventral organisms (order Marchantiales (sensu Bold et al. 1984)) usually
have some order of internal differentiation: photosynthetic cells, air chambers, and storage
tissues; sporophyte is compact and often lacks seta with a one-layered capsule (sporangium)
wall. Rhizoids are sometimes no more than a single cell protuberance.
- In Marchantia, the thalluse often shows dichotomous branching. Upper surface is divided
into a single layer of polygonal air chambers, each with a central air pore; cutin is found on
the surface of the plant. Each air chamber is surrounded by photosynthetic cells and
covered by an epidermis. The remainder of the thallus is comprised of densely arranged
parenchymatous cells (prob. serve as storage cells).
LEAFY liverworts (i.e., Porella):
- contain ca. 4000 species; particularly abundant in tropics and subtropics
- often superficially resemble mosses
- leaves are bilobed, folded and only one cell thick.
- plants are strongly dorsiventral with 2 rows of lateral leaves and a third row of underleaves
(amphigastria); the latter are smaller and different in shape than the laterals (= anisophylly)
- appearance of 5 rows of leaves due to small ventral lobes on lateral leaves
- Porella is strongly dioecious with antheridia borne in the axils of overlapping leaves, while
archegonia are borne on short, lateral branches of female plants in groups of 8-10.
II. DIVISION ANTHOCEROPHYTA: HORNWORTS:
- small group closely related to green algae
NOTEABLE GENERA: *(ca. 6 genera; maybe 100 spp.; the genus Anthoceros is the most
common example and is widely distributed around the world)
FOSSILS: thallose liverwort (Pallaviciniites devonicus) known from the Devonian of New
York state; diversification into thallose and leafy forms had occurred by the Carboniferous
NOTEABLE CHARACTERISTICS- Presence of one large bilobed chloroplast (or two smaller
chloroplasts) and pyrenoids (centers where glucose is condensed to starch within chloroplasts
of green algae and hornworts) attest to similarity to Colochaete
- Presence of stomata set liverworts and Colochaete apart
LIFE CYCLE: sporic; similar in most respects to liverworts.
GROWTH AND FORM:
- gametophytes are strongly dorsiventral, often rosettelike, and ca. 1-2 cm in diameter.
- either monoecious or dioecious
- antheridia and archegonia are sunken on dorsal surface of gametophyte (antheridia are
clustered in chambers)
- antheridial development keyed to light (4-12 hour days; inhibited by 18 hour days);
- archegonia differ from those of liverworts by the lack of a free, discernible jacket
layer
- archegonia with egg, ventral canal cell, and 4-5 neck canal cells; the neck
comprised of 6 vertical rows of neck cells.
- Anthoceros has extensive internal cavities filled with mucilage (instead of air chambers as in
liverworts); these cavities are often inhabited by Nostoc (cyanobacteria) which fixes
nitrogen for the host
- sporophyte of Anthoceros consists of a foot and a long, cylindrical sporangium
- meristematic growth occurs between foot and sporangium (intercalary meristem) and
growth continues as long as conditions are 'favorable'.
- the innermost section of the sporophyte is sterile and termed the columella
- a cylinder of sporogenous tissue surrounds the columella
- the surface layer of the sporangium is cutinized and develops stomata (with guard
cells) and is photosynthetic (will transfer photosynthates to gametophyte if
gametophyte is kept in the dark).
III. DIVISION BRYOPHYTA: TRUE MOSSES (ca. 600 genera, ca. 9500 spp.)
- Generally treated in three distinct classes: Bryidae (the "true" mosses), Sphagnidae (the peat
mosses) and Andreaeidae (the granite mosses).
- remarkably sensitive to air pollution (like lichens)
GROWTH AND FORM:
Gametophytes of two general growth patterns: cushion mosses and feathery mosses
*cushion mosses put up long, slender setae that are topped by spore capsules (= sporophytes)
*feathery mosses bear lateral spore capsule
GAMETOPHYTES develop from single apical meristematic cell similar to that found in
liverworts BUT they develop in two distinct stages: PROTONEMA (filamentous growth that
develops from germinating spore; protonema is platelike in Sphagnum) and LEAFY
GAMETOPHYTE
- cells of protonema occur in a single layer
- leafy gametophytes develop from buds on protonema
Gametophyte of mosses is leafy and usually upright rather than flat as in liverworts
- gametophytes range in size from 0.5 mm to 50 cm in length
* hydroids: central strand of water conducting tissue in gametophytes
- hydroids resemble tracheids in that they lack protoplast, but lack specialized wall
thickenings
* in some species, leptoids (sieve-like elements: food-conducting cells) surround hydroids
*leaves initially produced in three ranks, but become spiral in appearance
LIFE CYCLE: sporic
- meiosis occurs in spore capsules
- spores (1n) germinate into protonemata
- protonemata bud and develop leafy gametophytes (male and female)
- antheridia and archegonia develop on male and female leafy gametophytes, respectively
- antheridia produce biflagellate sperm; found in structures called splash cups
- sperm can travel great distances either by insects or by being splashed by rain
- archegonia produce an egg
- sperm (biflagellate) swim to archegonia and fuse with egg
- embryo develops, divides and young sporophyte grows attached to female leafy
gametophyte with the development of foot embedded in gametophyte
- sporophyte grows, develops spore capsule (at apex of seta or stalk in most species; seta
lacking among granite mosses), meiosis occurs and spores are produced
- calyptra, derived from archegonium, often remains with capsule
- young sporophytes contain chloroplasts and are photosynthetic
- dispersal of spores occurs when calyptra falls off and operculum (lid of capsule) pops off
leaving the peristome (a ring of teeth at the apex of the capsule) surrounding the
opening of the capsule (peristome found only among the class Bryidae; absent among
other two classes). Each capsule is capable of shedding up to 50 million haploid spores.