Transcript Understanding Our Environment

The Seedless Vascular Pants:
Ferns and Their Relatives
Outline
•
•
•
•
•
Phylum Psilotophyta (Whisk Ferns)
Phylum Lycophyta (Club Mosses)
Phylum Equisetophyta (Horsetails)
Phylum Polypodiophyta (Ferns)
Fossils
Features of Seedless Vascular Plants
1. Xylem and phloem present
• internal conducting tissues for water
and food, respectively
2. Spores, but no seeds
3. Ferns and relatives ("fern allies")
Classification of Seedless Vascular Plants
1. Phylum Psilotophyta (Whisk Ferns)
• no true leaves or true roots
2. Phylum Lycophyta (Club Mosses and Quillworts)
• small leaves with a single vein called microphylls
(most photosynthetic)
3. Phylum Equisetophyta (Horsetails & Scouring Rushes)
• ribbed stems containing silica deposits and whorled
leaves
4. Phylum Polypodiophyta (Ferns)
• large, complex leaves called megaphylls (more than
one vein)
Phylum Psilotophyta
•
The Whisk Ferns
 Loosely resemble small, green whisk
brooms.
 Structure and Form
- Sporophytes consist almost entirely of
dichotomously forking aerial stems.
 Have neither leaves nor roots.
 Enations superficially leaflike,
photosynthetic flaps of tissue,
spirally arranged along stems.
Life Cycle of the Whisk Fern Psilotum
1. Small sporangia borne on short stubby branches
2. Meiosis occurs in sporangia producing meiospores
3. Meiospores germinate slowly on soil or bark of tree ferns
4. Gametophytes found beneath the soil, very small (2 mm X 6 mm)
5. Archegonia and antheridia produced on this colorless gametophyte
6. Fertilization occurs in the archegonium
7. Sporophyte develops from the zygote
Fossil Whisk Fern Look-Alikes
1. Fossils resembling Psilotum present in Silurian formations.
2. Rhynia and Zosterophyllum
- likely ancestors of club mosses (lycopods)
Fig. 21.1
Phylum Lycophyta
•
Ground Pines, Spike Mosses, and Quillworts
 Collectively called club mosses.
- Only two living representatives of two
major genera.
 Lycopodium (50 species)
 Selaginella (700 species)
 Sporophytes have small leaves called
microphylls.
 Have true roots and stems.
Phylum Lycophyta
•
Lycopodium - Ground Pines
 Often grow on forest floors.
 Resemble little Christmas trees, complete
with cones.
 Stems are simple or branched.
- Develop from branching rhizomes.
Fig. 21.3
Reproduction in the ground pine Lycopodium
1. Strobilus (conelike stucture)formed in many
species.
2. Sporophylls with sporangia. Meiosis occurs in
sporangia.
3. Meiospores germinate in the soil and produce
gametophytes with archegonia and antheridia.
4. Fertilization occurs in archegonium, producing
zygote.
5. Zygote develops into mature sporophyte.
6. Asexual propagation may occur by bulbils, small
small budlike structures produced in the axils of
leaves.
Phylum Lycophyta
•
Selaginella - Spike Mosses
 Especially abundant in tropics.
 Branch more freely than ground pines.
 Leaves have a ligule (an extra appendage)
on upper surface.
 Produce two different kinds of spores and
gametophytes (heterospory).
Fig. 21.5
Reproduction in the spike moss Selaginella
1. Sporangia produced on microsporophylls
and megasporophylls.
2. Microsporangia and megasporangia
produce microspores and megaspores.
3. Microspores develop into male gametopyte.
4. Megaspores develop into female
gametophytes.
5. Gametophytes develop within the confines
of the microspore and megaspore walls.
6. Fertilization and development of
sporophytes similar to ground pines.
Phylum Lycophyta
•
•
Isoetes - Quillworts
 Most found in areas partially submerged in
water, and least part of the year.
 Long microphylls (grass-like in appearance).
 Microphylls are arranged in a tight spiral on
a stubby stem.
 Ligules occur towards leaf base.
 Corms have vascular cambium.
Reproduction
Similar to spike mosses.
Fig. 21.7
Human & Ecological Relevance of Club Mosses and
Quillworts
1.
2.
3.
4.
5.
Little economic importance.
Lycopodium: spores used as flash powder and other uses.
Selanginella: resurrection plants, sold as novelties.
Lycopodium: woven into wreaths and holiday decorations.
Isoetes: quillwort corms can be eaten by animals, birds,
and humans.
Phylum Equisetophyta
•
The Horsetails and Scouring Rushes
 Structure and Form
- About 25 species scattered through all
continents.
- Significant silica deposits accumulate on
the inner walls of the stem’s epidermal
cells.
- Branches, when present, are normally in
whorls at regular intervals along the
jointed stems.
Phylum Equisetophyta
•
•
•
•
Both branched and unbranched species have
tiny microphylls in whorls at the nodes.
Leaves fused at their base forming a collar.
Stems are distinctly ribbed and have obvious
nodes and internodes.
 Pith breaks down at maturity leaving a
central canal
 Vascular tissues with carinal canals (water).
Cortex with vallecular canals (air)
 Aerial stems develop from rhizomes
Reproduction
Fig. 21.10
Phylum Equisetophyta
•
Human and Ecological Relevance
 Many giant horsetails used for food.
 Scouring rush stems used for scouring and
sharpening.
Phylum Polypodiophyta
•
The Ferns
 Structure and Forms
- Approximately 11,000 known species of
ferns vary in size from tiny floating forms
less than 1 cm to giant tropical tree ferns
up to 25 m tall.
 Fern leaves are megaphylls that are
commonly referred to as fronds.
 Typically divided into smaller
segments.
Fig. 21.16
Spore Release From a Fern Sporangium
Phylum Polypodiophyta
•
Human and Ecological Relevance
 Extremely popular house plants.
- Serve as air filters.
 Cooked rhizomes serve as food.
 Folk Medicine
 Fronds used in thatching houses, weaving
baskets.
Fossils
•
A fossil is generally defined as any
recognizable prehistoric organic object
preserved from past geological ages.
 Conditions of formation almost always
include quick burial in an accumulation of
sediments.
- Hard parts more likely preserved than
soft parts.
Fossils
•
Molds, Casts, Compressions, and Imprints
 After being buried in sediment, the organic
material may be slowly washed away by
water percolating through the rock pores.
- If air space remains - Mold
- If silica fills space - Cast
 Compression takes place when objects are
buried by layers of sediment and greatly
compressed so that only a thin outline is
left.
Fossils
•
Petrifications
 Petrifications are uncompressed rock-like
material in which the original cell structure
has been preserved.
Review
•
•
•
•
•
Phylum Psilotophyta (Whisk Ferns)
Phylum Lycophyta (Club Mosses)
Phylum Equisetophyta (Horsetails)
Phylum Polypodiophyta (Ferns)
Fossils
Copyright © McGraw-Hill Companies Permission Required for Reproduction or Display