Biology 2500

1
Lecture 12

• Biology 2500
• Chapter 19 Seedless Vascular Plants

2
Learning Objectives

• Define
• Chert
• Axes
• Stroboli
• Sporophylls
• Contrast
• Sporangia placement on Cooksonia, Zosterophyllum,
  Lycopodium
• Megasporophylls vs. microsporophylls
• Discuss
• Importance of the Rhynie chert

3
Phylum Rhyniophyta

• Rhyniophytes
• Early vascular plants
• No leaves!
• Just twigs called axes
• Had sporangia on tips of terminal twigs
• No roots, but had highly branched rhizoids
• Includes Cooksonia

4
Cooksonia

• The oldest rhyniophyte
• Known from the Devonian (see Devonian Times
  website)
• The smallest, simplest vascular plant ever found
  in fossil record!
• First discovered in the Rhynie chert of Scotland
• Chert is a type of quartz
• True xylem found in fossils
• Only about 6.5 cm tall
• Towered above most non-vascular plants
• Bifurcating plant body

5
Cooksonia Websites

• University of Munster website on Rhynie Chert
• Hans Paleobotany Pages website

6
Phylum Zosterophyllophyta

• Like the rhyniophytes, also leaveless, bifurcated
• Placement of sporangia was different!
• On the sides of stems, hence laterally-borne
  sporangia

7
Phylum Lycophyta

• Arose from the Zosterophyllophytes
• Include
• Club mosses
• Resurrection plant
• Quillworts

8
Lycopodium

• The club mosses
• Gametophytes
• Still require water for reproduction
• Some of them are sub-terranean
• Sporophytes
• Each has numerous sporangia
• Sporophylls little leaf-like structures bearing
  sporangia
• Stroboli clusters of sporophylls (singular
  strobolus)

9
Selaginella

• The Resurrection plant
• Heterosporous and unisexual
• Makes separate male and female gametophytes
• Megasporophylls carry megasporangia
• Microsporophylls carry microsporangia

10
7th Inning Stretch