Lecture 3: Lycopsids: Ancient plants in a modern world

Question 1

3 facts about lycopsids

Answer 1

• most primitive extant vascular plants (lignified &most basal)
• sister group to all other vascular groups
• till present today &therefore be easily studied

Question 2

The _____ is the dominant generation in all vascular plants. Lycopsids have ______ and______ reproductive strategies.

Answer 2

sporophyte
homosporous
heterosporous

Question 3

Tracheophytes:

Answer 3

vascular plants

Question 4

Are tracheophytes or Bryophytes better adapted for life on land?

Answer 4

Tracheophytes because the sporophyte phase of the life cycle is dominant over the gametophyte phase and the sporophyte has lignified conducting tissues

Question 5

why are lignified conducting tissues beneficial?

Answer 5

provide greater support and are a more efficient transportation system (i.e. vascular system)

Question 6

Due to lignified conducting tissues tracheophyte sporophytes can

Answer 6

grow larger and exploit different body plans

Question 7

Reproduction example: Homosporous. Dominant Sporophyte generation

Answer 7

1) Sporophyte grows (2n)
2) Spores release
3) Meiosis occurs (=4 Xn)
4) Lands on damp soil
5) Sperm swims over to egg, gametophyte forms
6) Grows and produces sporophyte spores
7) & REPEAT

Question 8

What must be present for reproduction to occur?

Answer 8

H2O

Question 9

The living Lycopsids

Answer 9

• Lycopodium
• Phylloglossum
• Selaginella
• Isoetes

Question 10

The living Lycopsids : Lycopodium

Answer 10

• sometimes subdivided into 3 genera; 200 species; worldwide distribution
• roots
• leaves eligulate (not ligulate) (no scale inserted in the upper surface of the microphylls & sporophylls)
• microphylls
• Sporophylls
• HOMOSPOROUS
• Gametophytes may form at the surface or be subterranean.
• Archegonia have a relatively conspicuous neck
• spermatozoids are biflagellate

Question 11

Lycopodium if gametophytes are underground:

Answer 11

spores are long lived and washed deep into the soil before they germinate. The gametophyte is subterranean. IT is saucer-shaped with sex organs produced on a cushion in the central region.

Question 12

The living Lycopsids:

Phylloglossum

Answer 12

• 1 species : Australia

- Noteworthy features: Forms tubers; spermatozoids multi flagellate

Question 13

The living Lycopsids: Selaginella

Answer 13

• 700 species
• Microphylls ligulate (minute tongue-like ligule inserted into the upper side of the leaf close to the axis)
• always have strobili (reproductive cone like structure)
• HETEROSPOROUS
• stobili contain both micro&megasporangia located in different parts of the strobilus
• spermatozoids are biflagellate
• Female gametophyte protrudes from megaspore as an irregular cushion bearing rhizoids and archegonia in the central region. The archegonia have short necks.

Question 14

Reproduction example 3:

Dominant Sporophyte generation. HETEROSPOROUS

Answer 14

1) Sporophyte (2n) grows but has two different types of spores (mega and micro)
2) Micro spores are released and meiosis occurs (4n)
3) Mega spores are released and meiosis occurs forming 4n
4) If mega land near micro spores can swim over to mega (male to female) H2O required
5) produces sporophyte and REPEATS

Question 15

Pros to HETEROSPOROUS reproduction

Answer 15

• megaspores contain lots of H2O & starch
• Meaning they can survive for longer, living off their reserves
• can grow in periodically damp environments, still relies on water
• into of outbreeding, reproduction between different plants. Unlikely mega&micro spore from sae plant will land next to each other.

Question 16

The living Lycopsids: Isoetes

Answer 16

• 150 Species; aquatic
• These plants have a distinctive & remarkable rush-like habit. They are either aquatic or subject to periodic inundation.
• They have a short, fleshy, upright rootstock (that occasionally dichotomizes [splits in two]). Each branch bears a tuft of quill-like microphylls that are ligulate. In aquatic species the microphylls lack stomata.
• Heterosporous. The leaves first formed in a seasons growth bear megasporangia while those formed later bear microsporangia.

Question 17

Early land plant fossils can be very informative:

Answer 17

• many fossils can be found and compared to living organisms
• comparison of extant and extinct organisms
• well preserved, such as from the equatorial rainforest of the carboniferous, which were full for arborescent (tree like) lycopsids

Question 18

microphylls

Answer 18

small leaf

Question 19

Origin of leaves:

Answer 19

1) reduction
2) Enation
3) Sterilisation