Pteridophytes (ferns, whisk ferns, horsetails)

 

A.    Definition of kingdom to which it belongs

a.       Pteridophytes belong to the Kingdom Plantae

                                                              i.      Large, compound leaves, with underground rhizomes

                                                            ii.      Xylem and phloem rely on spores not seeds

                                                          iii.      Nonseed tracheophytes (vascular plant)

                                                          iv.      Ferns, horsetails, and whisk ferns form a clade

1.      Were once separate and treated as distinct phyla

b.      Mainly found in tropics or subtropical environments                                                            

c.       Moist, shaded habitats

d.      “ferns and fern allies”

e.       Fern allies are virtually living fossils today

f.       Do not produce flowers

g.      Nonseed tracheophytes

h.      Reproduce by spores (like mosses), but have a vascular system for fluid transport.

i.        Differentiation between main axis and side branches

 

B.     General biology, major distinguishing characteristics (morphology)

a.       (Morphology is outcomes of ecological and evolutionary adaptions of organisms to changing environements that ultimately influence nature of diversity and distribution.)

b.      Ferns

                                                              i.      Most abundant and diverse of nonseed tracheophytes today

                                                            ii.      12,000 species, first appeared during Devonian period.

                                                          iii.      97% of species; leptosporangiate ferns, constitute monophyletic group

1.      Differ from other ferns by having sporangia with ones only one cell think

2.      Borne on a stalk

                                                          iv.      Evolved large, complex leaves (fronds)

                                                            v.      Sporophytes (diploid generation in the life cycle of a plant, and that produces haploid spores by meiosis)  

1.      Sporophytes of ferns have true roots, stems, leaves like those of seed plants

                                                          vi.      Leaves large with branching vascular strands.

                                                        vii.      Some species have small leaves (result of evolutionary reduction)
Still are megaphylls (more than one vascular strand)

                                                      viii.      During development, fern frond unfurls from tight “fiddlehead”

                                                          ix.      Fern leaves grow up to 30 meters long, climbing organs

                                                            x.      Require water for transport of male gametes to female gametes

                                                          xi.      Inhabit shaded, moist woodlands and swamps

                                                        xii.      Tree ferns reach up to 20 meters in height

1.      Not as rigid as woody plants

2.      Poorly developed root systems

3.      Grow in ravines or beneath trees in forests

                                                      xiii.      Sporangia found on undersurface of fronds

1.      May cover whole underside, or only edges

2.      Sporangia found in clusters; sori (singular, sorus)

 

c.       Whisk ferns

                                                              i.      Epiphytes (grow on other plants), may also grow in rich soil

                                                            ii.      Resemble most ancient tracheophytes

                                                          iii.      Lack roots, anchored instead by creeping stem; rhizome.

                                                          iv.      widespread in Tropics and Subtropics

                                                            v.      Two genera

1.      Psilotum

a.       Found in N. America, Caribbean, along Gulf, Atlantic Coasts, Asia, Pacific Islands.

b.      May also be found as common weed in greenhouses

c.       Escapes cultivations in regions with mild climate

d.      100 unusual breeds and highly prized by cultivators in Japan.

e.       Minute scales, no true leaves

f.       Grow up to 30cm + taller

 

2.      Tmesipteris

a.       Found in S. Pacific, Australia, New Zealand, New Caledonia

b.      Flattened photosynthetic organs (leaves)

c.       Largest leaves contain single vascular bundle; connects to central stele

d.      Reduced megaphylls, well-developed vascular tissue

                                                          vi.      Gametophytes live below ground, lack chlorophyll

1.      Depend on fungal for nutrition

d.      Horsetails

                                                              i.      Found in Europe, Asia, M. East, N. America.

                                                            ii.      Perennial (returns each year)

                                                          iii.      Hollow stems, shoots look like asparagus

                                                          iv.      Grow at bases of stem segments

                                                            v.      Was once dominant elements of Earth’s vegetation

                                                          vi.      Only few present day species

1.      Single genus Equisetum

                                                        vii.      Called “scouring rushes”

1.      Silica deposits in cell walls useful for cleaning.

                                                      viii.      True roots, branch irregularly

                                                          ix.      Sporangia curve back toward stem on ends of short stalks called sporangiophores

                                                            x.      Large sporophyte

                                                          xi.      Small gametophyte

                                                        xii.      Small leaves, reduced megaphylls, form distinct whorles (circles) around stem.

                                                      xiii.      Growth in horsetails originate from discs of dividing cells above each whorl of leaves

1.      Each segment of stem grows from its base.

2.      Basal (growth at base) growth uncommon in plants, common in grasses

 

C.     Major evolutionary groups (evolutionary background/classification)

a.       Arose from rhyniophyte-like ancestors.

                                                              i.      Pteridophytes featured specializations not found in ancestor

1.      True leaves

2.      True roots

3.      Differentiation between two types of spores

a.       Homosporous plants bear single type of spore

b.      Heterosporous plants bear two types of spores into distinctively male and female gametophytes

                                                                                                                                      i.      Megaspore à female, larger

                                                                                                                                    ii.      Microspore à male, smaller

                                                            ii.      Rhiniophytes had only rhizoids arising from rhizome which gathered water and minerals

1.      Rhizome – hairlike, absorptive organ

b.      Pteridophytes are apart of the tracheophytes

                                                              i.      Tracheophytes – vascular plant (including gymnosperms, angiosperms)

                                                            ii.      Pteridophytes are nonseed trecheophytes


D.    Major phyla/classes of the organisms in kingdom

a.       Phylum Pteridophyta form a clade

                                                              i.      Include horsetails, whisk ferns, ferns

                                                            ii.      Whisk ferns and horstetails are monophyletic (share common ancestor), ferns do not.

                                                          iii.      Ferns (11,000+ species)

1.      Most widely distributed, 97% belong to single clade; leptosporangiate ferns.

                                                          iv.      Horsetails (few species, one genus)

1.      Grow at bases of stem segments

2.      “scouring rushes” useful for cleaning

3.      Reduced megaphylls

                                                            v.      Whisk ferns (two genera)

1.      Resemble most ancient tracheophytes

2.      Two genera Psilotum and Tmesipteris

 

E.     Distribution of the organism in the biosphere

a.       Most found in rainforests; tropical and temperate

                                                              i.      Habitats range from sea-sprayed cliffs through fresh water rivers to semi-desert of arid climates.

                                                            ii.      No marine species, found wordwide, except Antarctica and some islands.

                                                          iii.      Horsetails

1.      Found in Europe, Asia, M. East, N. America.

                                                          iv.      Whisk ferns

1.      Psilotum

a.       Found in N. America, Caribbean, along Gulf, Atlantic Coasts, Asia, Pacific Islands.

2.      Tmesipteris

a.       Found in S. Pacific, Australia, New Zealand, New Caledonia


F.      Diversity of the organism and its adaptations to environment

a.       Terrestrial

                                                              i.      Have erect/creeping stems and leaves held upright.

                                                            ii.      Unbranched stems, radial, stout, and woody

                                                          iii.      Fronds may have long stems

                                                          iv.      A number of species live on rocks, rock crevices

b.      Epiphyte (grows on another plant)

                                                              i.      stems attached to or rooted on trunks or branches of trees

                                                            ii.      long fronds climb into trees

                                                          iii.      compact or short to long-creeping stems

1.      start on the tree or on the ground

2.      attached to the tree and are not reliant on the soil

c.       Aquatic

                                                              i.      number of ferns are truly aquatic, a much greater number are subaquatic (growing beside and periodically flooded by streams)

                                                            ii.      compact or shortly creeping stems and can be free-floating on the surface of the water (Azolla, Salvinnia),

                                                          iii.      completely submerged and rooted in the bottom sediment (Isoetes),

                                                          iv.      rooted and emergent (Marsilia) or a

                                                            v.      combination of all three (Ceratopteris).


G.    Economic/human use

a.       Forests of horsetails, tree ferns flourished in tropical swamps of what would become N. America and Europe ( Devonian period)

                                                              i.      Died in anaerobic environment

                                                            ii.       are now huge deposits of coal.

                                                          iii.      Fossil fuels used today

1.      Responsible for much of todays energy source

2.      Not renewable

3.      Used more rapidly than it is replaced

4.      Said to be responsible for global warming

b.      Tree ferns may be used as building material in tropical areas

c.       Fiddlehead of ostrich fern – vegetable, general cuisine

d.      In Western society, used for landscaping

e.       Ferns of genus Azolla, are tiny aquatic floating fern, used as fertilizer in rice paddies of SE Asia

f.       Horsetail – herbal remedy, above ground part of plant (dead/alive)

                                                              i.      Used to stop bleeding

                                                            ii.      Treat TB

                                                          iii.      And kidney problems

                                                          iv.      Plants stem holds silica

1.      Mend broken bones and form collagen

2.      Prevent osteoporosis

                                                            v.      Polishing metal, particularly pewter

1.      When dry, silica crystals form in stem and branches to give scratching effect.

2.      “scouring rushes”

H.    Details of an interesting study using organisms from the group

a.       Life history, diversity, and distribution: a study of Japanese pteridophytes

                                                              i.      Analyzed 600 species

1.      102 species endemic (disease) to Japan

2.      Chromosome numbers known for 596 species

3.      On distribution, reproduction, chromosome number

                                                            ii.      Species richness was greater in groups of single reproductive modes

                                                          iii.      Distribution greatest in species with multiple reproductive modes

1.      Sexual/asexual

a.       Able to overcome harsh conditions

                                                          iv.      Geographical ranges varied greatly with species with small chromosome numbers

                                                            v.      Ranges were restricted with species with relatively high chromosome numbers

1.      Ages of polyploids (plants whose chromosome exceeds twice basic set of chromosomes) may be responsible

2.      Prolonged environmental changes in past

                                                          vi.      No clear relationship between spore size and chromosome number

                                                        vii.      Habitat availability, rather than dispersal, may be a limiting factor for distribution in Japan

                                                      viii.      Most Pteridophytes are perennial; long geological history

                                                          ix.      No significant difference between spore size of endemic and non- endemic

                                                            x.      Spore size not limiting factor in dispersal

                                                          xi.      Possible that species in open habitat disperse more rapidly

I.       List of references

 

a.       Croft, J. (1999). Brief introduction to ferns. Retrieved July 25, 2007, from Pteridophytes: Links to the Ferns and their Allies Web site: http://www.anbg.gov.au/fern/fern-links.html

 

b.      Guo, Q. (2003).Life history, diversity and distribution: a study of japanese pteridophytes. Ecography. 26, 129-138.

 

c.       Hawkins, E.B. (2006). Horsetail. Retrieved July 26, 2007, from Univ of Maryland Medical Center Web site: http://www.umm.edu/altmed/articles/horsetail-000257.htm

 

d.      Purves, W.K., Sadava, D., Orians, G.H., & Heller, H.C. (2004). Life the science of biology. Sunderland: Sinauer Associates.

 

e.       Speer, B. R. (1995). Introduction to the psilotales: the whisk fern. Retrieved July 26, 2007, from Berkeley Plants Web site: http://www.ucmp.berkeley.edu/plants/pterophyta/psilotales.html