Lecture 8 (pt2) - Monilophytes

Question 1

Equisetales (horsetails) - when? how many?

Answer 1

• Equisetales (= sphenophyta = equisetophyta) -> date back to Devonian
• Counting fossils, there were once 5 orders and 12 genera now only 1. equisetum with 15 species ww

Question 2

Equisetales (horsetails) - origin

Answer 2

• Stem is dominant origin
  ○ Jointed at nodes where there are scale like leaves
  ○ At first photosynthetic, soon drying to brown
  Stem is high in silica and photosynthetic, may be branched (horsetails) or unbranched (scouring rushes)

Question 3

Monilophytes

Answer 3

= spores + true leaves

Question 4

Equisetales (horsetails) - stem

Answer 4

contains a eustele btwn nodes, but siphonostele, with no leaf gaps at nodes (therefore, leaves are microphyllous)

Question 5

Equisetales (horsetails) - dominant species

Answer 5

During late devonian and carboniferous periods (370-300 MYA), tree-like Calamites was a dominant member of the forests, along with Lepidodendron and Sigillaria (lycopods)

Question 6

Equisetales (horsetails) - traits

Answer 6

• Homosporous: spores germinate to form bisexual (F first, becoming M) or male gametophytes
  
  • Sperm from antheridia swim to egg of an archegonium
  • Gametophytes are small, photosynthetic, independent
  • Rhizomes and roots are jointed and perennial
  • Vegetative propagation in horsetails in very important
    ○ form large clonal patches in fields = hard to get rid of
  • Good to clean pots with but not to eat
    ○ Contain thiaminase -> breaks down vitamin thiamin

Question 7

Equisetales (horsetails) - strobili

Answer 7

• Strobili (spore cones) are produced either at tips of vegetative shoot, or on special fertile stems (E. arvense = weed)
  
  • Strobili bears (modified microphylls) sporangiophores
    ○ Hexagonal
    ○ produce several sporangia on inner surface
    ○ When mature, strobilus elongates exposing sporangia
  • Spores (high chromosome count 100+) have 4 appendages = elaters
    -> Aid in dispersal of spores from sporangia

Question 8

Equisetales (horsetails) - lifecycle

Answer 8

Strobilus -> sporogenous tissue (2n) -> meiosis -> spores (n) -> elaters wrap around spores -> germinating spores -> rest of life cycle is same as those in lecture 7 ie. Archegonium and antheridium

Question 9

Ferns - what, when, how many

Answer 9

• Monilophyta minus horsetails and whisk ferns
  
  • in the carboniferous (350 MYA), and in late carboniferous (320-290 MYA) = “age of ferns”
  • One tree like fern of the Marattiales (eusporangiate and homosporous), Psaronius was abundant
  • True megaphyllous leaves
  • 11 000 sp
    ○ Mostly in tropics
    ○ Variation in form -> grass like to trees
    § Tree trunks are pseudo trunks made up of stems
    □ No true wood or secondary growth
• Ontario has 55 ferns all herbaceous

Question 10

fern life cycle

Answer 10

Adult sporophyte (2n) -> sporogenous tissue (2n) -> meiosis -> mature dehiscing sporangium with spores -> spore (n) -> young gametophyte (n) -> immatures archegonium (egg 1n) or immature antheridium (spermatogenous tissue 1n) -> sperm (1n) swims to egg -> fertilization -> zygote (2n) -> embryo (2n)

Question 11

importance of monilophytes

Answer 11

• Economic
  ○ Other than Azolla-Anabaena, spore-bearing vascular plants are of minor importance
  
  • Ecological
    ○ Ferns and fern allies form dominant ground cover in many moist, shaded forests, especially in tropics
  • Evolutionary
    ○ The great diversity of ferns is recent (cretaceous)
    Common ancestors that lead towards seed ferns were also common ancestors of flowering plants