Unit 2 Earliest Vascular Plants

Question 1

What are the three types of the earliest vascular plants?

Answer 1

1) Rhyniophyta 2) Zosterophyllophyta 3) Trimerophytophyta

Question 2

When do the earliest land plants appear?

Answer 2

Date back to 460 million years ago in the Ordovician

Question 3

When were vascular plants found?

Answer 3

At the close of the Devonian (360 mya)

Question 4

When did vascular plants evolve?

Answer 4

50 million year period

Question 5

Rhyniophyta

Answer 5

Contains the simplest and oldest known vascular plants -most lived in mud flats, marshes or bogs

Question 6

Anatomy of Rhyniophyta: stem, root, sporangia

Answer 6

1) Dichotomous branching aerial stems arising from a horizontal underground stem 2) Stems are naked-no appendages 3) Roots are absent through rhizoids anchor the underground stem 4) Sporangia are terminal on the branches 5) Vascular system-simple stem (centrach xylem)

Question 7

What would a cross-section of Rhynia look like? (Stem)

Answer 7

A cylinder of primary xylem surrounded by primary phloem (centrach)

Question 8

What type of vascular tissue did Rhynia have?

Answer 8

Tracheids-anchor thickenings

Question 9

What type of vascular tissue evolves around this period?

Answer 9

1) Bryophyte hydroid 2) Tracheids

Question 10

What is a bryophyte hydroid?

Answer 10

It is not a tracheid -These can collapse under water stress due to not having lignin in the cell walls

Question 11

Zosterophyllophyta

Answer 11

-Similar to Rhyniophyta but larger

Question 12

Anatomy of Zosterophyllophyta: stem, sporangia

Answer 12

1) Stem has exarch xylem 2) Stems were either smooth or covered with multicellular “spines” 3) Stems were leafless and dichotomously branched 4) Sporangia were kidney-shaped or globose and borne laterally (not terminal)

Question 13

Trimerophytophyta

Answer 13

May represent the ancestor of pteridiophytes and progymnosperms -larger/complex than the other two phyla

Question 14

Anatomy of Trimerophytophyta: Stem, sporangia

Answer 14

1) Tree-like (appears to be a main trunk) since the branching is unequally dichotomous 2) Lacked leaves 3) Smaller branches terminated in sporangia

Question 15

What is centrach xylem?

Answer 15

Vascular cells mature from the center of the axis to the periphery -single protoxylem strand is found in the center of the axis, and the metaxylem formed around it

Question 16

What is exarch xylem?

Answer 16

Vascular cells develop from the outside, inwards towards the center -the protoxylem is found on the periphery, and metaxylem is closed to the center of the stem or root

Question 17

What is primary xylem?

Answer 17

The xylem formed during the primary growth from procambium of root and shoot apex -Growth in length

Question 18

What is secondary xylem?

Answer 18

Refers to the formation that occurs after the vascular cambium’s secondary growth -Growth in diameter -Consists of larger-sized vessels and tracheids

Question 19

What is the oldest known vascular plant and which phylum does it belong to?

Answer 19

Cooksonia (Rhyniophyta)

Question 20

What are the two oldest Lycopodiophyta orders?

Answer 20

1) Asteroxylales
2) Protolepidodendrales

Question 21

Asteroxylales

Answer 21

• Had smooth horizontal rhizomes and aerial branches with small leaves
• sporangia were borne laterally
• homosprorus

Question 22

Protolepidodendrales

Answer 22

• Small creeping, herbaceous plants
• Baragwanthia (early Devonian)

Question 23

What is a later Lycopodiophyta order?

Answer 23

Lepidodendrales