Kingdom Plantae

 

Plants appeared on land about 425 million years ago and the evolutionary history of the plant kingdom reflects increasing adaptation to the terrestrial environment.

 

General Characteristics of Plants:

1.      Multicellular eukaryotes that are photosynthetic autotrophs.

2.      Contain chloroplasts with the photosynthetic pigments chlorophyll a, and b and carotenoids.

3.      Cell walls containing cellulose.

4.      Food reserve is starch that is stored in plastids.

5.      Aerial parts are coated with a waxy cuticle that helps prevent desiccation.

6.      Gas exchange cannot occur across the waxy cuticle so specialized openings on the under surface of the leaf, called stomata, allow gas exchange.

7.      Reproductive adaptations necessary as plants moved from and aquatic to a terrestrial environment 

a)      Gametes must be dispersed in a nonaquatic environment.  Plants produce gametes within gametangia, organs with protective jackets of nonreproductive cells that prevent the gametes from drying out.   The ovum is fertilized within the female organ.

b)      Embryos must be protected against desiccation.  The zygote develops into an embryo that is retained for awhile within the female gametangia’s jacket.

8.      All plant life cycles have “Alternation of Generation”.

a)      A haploid  gametophyte generation produces and alternates with a diploid sporophyte generation.  The sporophyte in turn produces the haploid gametophyte.

b)      The life cycles are heteromorphic; sporophytes and gametophytes differ in morphology.

c)      The sporophyte is larger more conspicuous and more dominate in all except the  Bryophytes and their relatives.

 

Plants evolved 425 million years ago during the Silurian period.  They are believed to have evolved from green alga probably charophytes.  Evidence includes:

a)      These algae have a cell wall composition similar to plants. 

b)      The structure and function of the chloroplasts is homologous in these two groups.  Both have chloroplasts with thylekoid membranes stacked  as grana.

c)      Plant chloroplast DNA most closely matches that of charophytes.

d)      Green algae and plants contain cellulose in their cell walls

e)      Similarity in mitosis and meiosis

f)        Charophyte sperm are more similar to certain plants than to other green algae

g)      DNA and rRNA are similar in charophytes and plants.

 

 

 

 

 

 

EMBRYOPHYTES-Embryo, as well as gametes, enclosed in protective jacket of non-reproductive cells.  Thallophytes-lacking vascular tissue and therefore lacking true roots stems and leaves.

 

Division Bryophyta

 

Characteristics

1.      Lack vascular tissue. Imbibe water though diffusion and capillary action.

2.      Require environmental water to reproduce.  Their flagellated sperm must swim from the antheridium to the archegonium to fertilize the ovum.

3.      With a waxy cuticle to prevent desiccation.

4.      With gametangia that protect developing gametes.

a)      Antheridium, male gametangia produces flagellated sperm.

b)      Archegonium, female gametangia, produces a single ovum and fertilization occurs within the gametangium and the zygote develops into an embryo within the protective jacket if the archegonium.

5.      Lack woody tissue and cannot support tall plants.

6.      Each plant grips the substrate with rhizoids.

7.      The gametophyte is the dominant, conspicuous generation.

 

Division Hepatophyta, Liverworts

 

Characteristics;

1.      Bodies divided into lobes (resembling the lobes of the liver).

2.      Life cycle similar to mosses.

3.      Lack vascular tissue.

4.      Require environmental water for fertilization.

5.      Can reproduce asexually from gemmae.

 

DivisionAnthocerophyta, Hornworts

 

Characteristics:

1.      Lack vascular tissue.

2.      Require environmental water for fertilization.

3.      Sporophytes are horn shaped elongated capsules that grow from the mat-like gametophyte.

 

 

 

 

 

 

 

 

 

TRACHEOPHYTES-Vascular  plants, with vascular tissue.

 

Division Psilophyta Ancient plants that flourished millions of years ago.  Only 2 genera exist today.

 

Characteristics:

  1. Sporophyte generation is dominant,
  2.  The gametophyte is independent of the sporophyte although very small.  The gametophyte is monoecious producing both antheridia and archegonia.
  3. With true stems, but with rhizoids in place of roots.
  4. No leaves.  The stems are green and carry on photosynthesis.
  5. Naked sporangia are borne on the branches.
  6. No vascular tissue.

 

Division Lycophyta, club mosses and ground pines. Example Lycopodium and Salaginella.

 

Characteristics:

  1. With vascular tissue(one vein, lacking in gametophyte), true roots, true stems (both rhizomes and erect) and small scale-like leaves(mesophylls)
  2. Sporangia borne in cone-like strobili at the tips of the stem.
  3. Homosporous producing monoecious gametophytes (Lycopodium) or heterosporous producing dioecious gametophytes ( Salaginella).
  4. Sporophyte is the larger more conspicuous, dominant generation.

 

Division Sphenophyta, horsetails

 

Characteristics:

  1. The sporophyte generation is the dominant generation.  Homosporous with spores borne on cone-like strobili  clustered at the tips of branches
  2. With true roots, stems(carry out most of the photosynthesis), and leaves (leaves are small, scale-like and occur in whorls).
  3. Body with a tough coating of silica.

 

Division Pterophyta, ferns

 

Characteristics:

  1. Leaves with many veins called fronds.  They are highly subdivided ( compound ).  The arise from a rhizome which has many small roots.  With true roots and stems as well.
  2. Reproduce vegetatively by extension of the rhizome underground.
  3. Sporophyte generation is the dominant generation.  The spores are produced in sporangia on the underside of the leaf.  Clusters of the sporangia are called sori.  It is homosporous and produces a monoecious gametophyte.
  4. The gametophyte is tiny, green and independent of  the sporophyte plant.  It does not have vascular tissue.

 

 

Gymnosperms-Naked seed, lack enclosed chambers in which seeds develop.

 

Division Coniferophyta (Conifers), largest division of gymnosperms.  Most are evergreens and include pines, firs, spruces, junipers, cedars, cypresses, and redwoods.

 

Characteristics;

  1. Needle shaped leaves.
  2. Vascular tissue is present in all parts of the sporophyte and very well developed.
  3. Sporophyte is large, conspicuous and dominant.
  4. Reproductive structures are produced mostly in cones.
  5. Transfer of the pollen, male gametophyte, to the female reproductive parts is via wind.  Water is not required for fertilization.
  6. Heterosporous, male and female gametophytes develop from different types of spores produced by separate cones.  Gametophyte is very tiny and develops within the body of the sporophyte, which provides nourishment, moisture and protection.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Division Cycadophyta Sago Palm, Leather leaf or Cardboard palm.

 

Characteristics;

  1. Palm like leaves which are tough and leathery and pinnately divided into many leaflets.
  2. Short woody stems.  The stem has a large pith, a thin vascular cylinder and a thick cortex
  3. All have two kinds of strobili borne on separate plants.

 

Division Ginkophyta Ginkgo or maidenhair tree

 

Characteristics:

1. Broad, fan-shaped leaves.  Profusely branched   and deciduous.

2. The strobili are of two kinds and borne on separate trees.

 

Division Gnetophyta Mormon tea, Ephedra

 

Characteristics:

  1. Stem, but no leaves.
  2. Desert plant.

 

Angiosperms-Flowering plants.  Most widespread and diverse of all plants.

 

Division Anthophyta

 

Characteristics:

  1. Most use insects and animals for transferring pollen and therefore are less dependent on wind and water.  Pollination is less random.
  2. Most angiosperms have vessel elements that are shorter, wider cells, which are arranged end to end forming continuous tubes.  Xylem is reinforced by other cells.
  3. Heterosporous.
  4. Ovules enclosed in a carpel.  After fertilization the carpel develops into a fruit.  With double fertilization.

 

Dicoteyledons

 

  1. Seeds with two cotyledons.

 

 

 

 

 

 

 

  1. Stems with a hollow cylinder of vascular tissue with functioning cambium.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  1. Leaves with netted veins forming an open system.  Leaves pinnate or palmate.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  1. Floral parts chiefly in fours or fives.
  2. Usually with a taproot system. Central stele consisting of pericycle and a thick walled xylem and thinner walled phloem. Vascular bundles arranged in a ring in the stem.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Monocotyledons

 

  1. Seeds with one cotyledon.

 

 

 

 

 

 

 

 

 

  1. Vascular bundles scattered in the stem.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  1. Leaves with parallel venation.

 

 

 

 

 

 

 

 

 

 

 

 

 

  1. Floral parts usually in 3’s or multiple of  3”s.

 

 

 

 

 

  1. Usually with a fibrous root systems.