Biology 2500

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Lecture 13

• Biology 2500
• Chapter 19 Seedless Vascular Plants

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Learning Objectives

• Discuss
• Importance of horsetails silicaceous ribs,
  delayed antheridium development
• Define
• Prothallus
• Circinate vernation
• Sorus
• Indusium

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Equisetum Basics

• Phylum Sphenophyta
• Equisetum the horsetails
• Leaves gathered in whorls at nodes (SIU website)
• Internodes are hollow
• Have silicaceous ribs (hence, the scouring
  rushes)
• Important evolutionary step some plants will
  later have silica in tissues as herbivore defense

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Interesting Facts about Equisetum

• Gametophytes either male or bisexual
• No females!
• In bisexual individuals, the archegonia develop
  before antheridia. Why?
• Sporophytes have 2 kinds of shoots
• Vegetative (photosynthetic)
• Fertile (but non photosynthetic) shoots (SIU
  website)
• Probably the oldest genus of plants still living
• The first big plants, some stems had 25 cm
  diameter

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Phylum Pterophyta (Ferns)

• In diversity, second only to flowering plants
• 11,000 species world wide (mostly tropical)
• 380 in US Canada
• 1000 in Costa Rica
• About 1/3 live as epiphytes

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Fern Reproduction

• Require water for sperm to swim
• Sporophytes large, gametophytes small
• There are tree ferns w/sporophytes 24 m tall,
  with 5 m leaves
• University of Sydney website
• Note prothallus, gametophyte, archegonium,
  antheridium

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Two Basic Types of Ferns

• Eusporangiate vs. Leptosporangiate

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Eusporangiate Ferns

• Eusporangia are thick-walled
• Derived from several epidermal cells

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Leptosporangiate Ferns

• Leptosporangia are thin-walled sporangia
• From single epidermal cell
• Ring of cells shrinks during dehiscence
• Snapping action shoots spores out
• U of West Indes website

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Leptosporangiate Ferns Order Filicales

• Typical of ferns people see locally
• Have fiddleheads (circinate vernation)
• Leaves unroll as they grow
• Tender apical meristem is protected
• Sori (plural of sorus)
• Brightly-colored bodies under leaves
• Sporangia are clustered here
• Indusia may cover
• Milwaukee Public Museum website

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