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KINGDOM PLANTAE
I. It seems almost certain that true plants have been derived from green algal
ancestors (Chlorophyta) because:
A. Both have chlorophylls A & B and carotenoids
B. Both use starch as their primary carbohydrate food reserve. And both deposit it in
the chloroplasts, not the cytoplasm as in other algal groups
C. Cellulose is the principle component of the cell walls in plants. Likewise many
green algae
D. All true plants form a phragmoplast during cell division. So do some green
algae
E. All true plants are oogamous. Some green algae are also oogamous
F. All true plants have an alternation of heteromorphic generations. So do many green
algae
II. True plants can be distinguished from green algae because they have adaptations
for life on land
A. The transition from water to land was a major step in the evolution of
organisms
B. In plants this required numerous structural and physiological adaptations, not
only to prevent drying out, but also to transport water and nutrients, and to facilitate
gas exchange
C. Two important reproductive adaptations were:
1. Formation of sterile jacket layers around the sperm and egg
producing cells of the gametangia to form antheridia
(male) and archegonia
(female)
2. Retention of the zygote within
the female gametangium and its development into an embryo
III. Two major types of true plants:
A. Vascular (higher) plants:
1. Have true conducting tissues
(xylem and phloem), leaves, stems and roots
2. The sporophytes are the dominant phase and
the gametophytes are much reduced
3. Constitutes the majority of plants
B. Non-vascular (lower) plants
1. Lack true conducting tissues,
leaves and roots. Since they lack elaborate conducting tissues they are relatively
small
2.
The gametophytes are the dominant phase and the sporophytes are dependent upon
them
3. Require water for fertilization so they must grow in moist or
seasonally moist habitats
There are three phyla of non-vascular plants, we will cover two of them:
I. Phylum Bryophyta - Commonly called mosses
A. About 9,500 species, all
of which are "leafy"
B. Have several celled rhizoids (liverwort rhizoids are single
celled)
C. Moss spores give rise to a "green algal- like" structure called a
protonema, which then gives rise to several
gametophytes (only some Liverworts have protonema)
D. Moss sporophytes typically have stomata (stomates), pores for gas
exchange (Liverworts lack them)
E. Many mosses have special water (hydroids) and food (leptoids) conducting
cells (Liverworts lack them)
F. Typical moss life cycle is on p.
419 of your text
1. Gametophytes are leafy, usually upright and they may reach lengths of up to 1
1/2 feet. The "leaves" are generally only one cell thick
2. Gametangia (archegonia and antheridia)
are usually produced at the tip of the main axis or on lateral branches
3. Sporophytes are borne on the
gametophytes and they usually consist of a capsule (sporangium)
borne on an elongated stalk called a seta
4. Young sporophytes have stomates for gas exchange and they may
undergo photosynthesis. Therefore they are not as dependent on the gametophyte as
liverworts
5. The calyptra (gametophytic tissue)
comes off and the capsule lid, the operculum, bursts off
6. A ring of
teeth, the peristome, is hygroscopic and aids
in spore dispersal. Each capsule may contain up to 50 million spores.
7. Asexual reproduction is via fragmentation or gemmae - small
multicellular bodies.
II. Phylum Hepatophyta - commonly called liverworts
A. About 6,000 species
B. Liverwort rhizoids are single celled (Mosses have several celled
rhizoids)
C. Only some Liverworts have protonema (Moss spores give rise to a protonema)
D. Liverworts lack stomata (stomates), pores for gas
exchange (Moss
sporophytes typically have them)
E. Liverworts lack conducting cells (Many mosses have special water
and food conducting cells)
F. Two growth forms of Liverworts:
1. Thallose - a thallus is an undifferentiated (no roots,
stems, leaves) plant body having distinct upper and lower surfaces. About 1/3 of
liverworts are thallose
2. Leafy - they have a leafy or moss-like
appearance. The "leaves" are only one cell thick. About 2/3 of liverworts are
leafy
G.
Marchantia is the typical thallose
liverwort. It grows on moist soil and rocks and consists of a flat unisexual thallus with
upright reproductive structures called antheridiophores
and archegoniophores which bear the
antheridia and archegonia, respectively. Following fertilization the sporophytes develop underneath the "fingers"
of the archegoniophores.
1. The life cycle of Marchantia is on p. 411 of your text
2. The enlarged archegonium is called a calyptra. At maturity the
sporophyte consists of a foot embedded in the archegonium, a seta or stalk, and a
sporangium. At maturity the calyptra falls off and the spores are shed following
dehiscence of the capsule. The sporangia contain elongate cells called elaters which are hygroscopic and aid in spore
dispersal.
3. Liverworts may also reproduce asexually by fragmentation or the production of gemmae
which are multicellular bodies that give rise to new gametophytes. They are located in
small splash cups.
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