Early Tracheophytes are the next level (after Bryophytes) of evolution to dry land.

Chapter 21b-The Early Tracheophytes

Tracheophyte refers to plants with true vascular systems comprised of phloem and xylem.

The vascular system allowed plants to move water from the soil to aerial portions of the plant.

Rhynia, an extinct early tracheophyte from about 400 million years ago had a simple vascular

system. Plants rarely exceeded 20 cm tall.

The fossil record of these early Tracheophytes has enabled botanists to reconstruct the likely evolutionary path from

Bryophytes to Tracheophytes.

This process included the following innovations:

1. a dichotomously branching sporophyte with multiple terminal sporangia

2. a free-living, nutritionally independent sporophyte that is prominent in the life cycle

3. a reduced gametophyte

4. lignified vascular tissue (xylem)

5. development of a main stem with side branches

Relationships among Early Tracheophytes

Tracheophytes that release spores rather than seeds.

These two lineages are characterized

by several morphological featues,

but also a major molecular feature.

Lycophytes

Zosterophyllophyta (extinct) were simple,

dichotomously branched plants that

lacked leaves and roots, much like Rhynia.

These plants show a gradation in complexity

from the fairly simple Zosterophyllophyta to

the Lepidodendrids.

Pteridophytes

The Lycophytes

The next innovation in the Lycophytes was the microphyll.

The final group, the Lepidodendrids, are extinct.

These tree-like plants were the major plant type of the extensive coal-age forests.

The Lycopodium group.

The first land plants with microphylls.

Lycopodium and related genera are mostly trailing plants, with short upright

branches that resemble thick mosses or pine seedlings.

Most commonly called club moss.

How does Lycopodium differ from a moss?

1. Major vegetative plant is the sporophyte.

2.The leaves of Lycopodium are microphylls.

3. The vascular tissue includes true phloem and xylem, with

lignin present in the xylem.

4. Roots with vascular tissue are present

Microphyll does not refer to size.

Instead, the name refers to the presence of only a single

vascular bundle in the leaf.

We will focus our discussion on the 3 extant groups of

Lycophytes:

-Lycopodium group

-Selaginella

-Isoetes.

The Lycopodium group.

The cross-section of a microphyll reveals its simple construction.

The Lycophyte life cycle starts with the mature sporophyte, the portion of the life cycle we generally see.

The Lycopodium life cycle starts with the mature sporophyte, the portion of the life cycle we generally see.

Numerous lateral sporangia produce haploid spores by meiosis.

Lycopodium is homosporous,

The sporangia consist of modified leaves called sporophylls arranged in a cone or strobilus.

The gametophytes are small, long-

living, and often subterranean.

They require an endosymbiotic

fungus to survive.

Each gametophyte produces egg

cells in archegonia and sperm in

antheridia.

The flagellate sperm swim to the

archegonium and fertilization

occurs.

The embryo develops and

ultimately grows into a mature

sporophyte.

Selaginella has another major innovation -- heterospory

Selaginella is the only living genus of this lineage, but it very

diverse, with about 700 species.

Most species produce a prostrate system of dichotomously branched stems covered with four rows of microphylls.

Isoetes is the last extant relative of the Lepidodendrids

Isoetes

Selaginella life cycle.

The sporophyte produces stobuli somewhat

like those of Lycopodium.

However, two types of sporangia are present

in each strobulus.

The microsporangia produce microspores.

The megasporangia produce megaspores.

There are about 125 species of Isoetes, most of which grow submerged in water.

They have the basic appearance of a grass or sedge, but the leaves are actually

microphylls (single vascular bundle)

Isoetes is linked to the extinct lepidodendrid group by several morphological features,

Fertilization occurs in the archegonium of the

megagametophyte.

The embryo develops, eventually becoming

the free-living sporophyte.

The (ferns and relatives)

We will briefly examine the features of each of the lineages of Monilophytes

This lineage is most closely related to the seed plants and

shares a number of features with that group.

Megaphylls

We will briefly examine the features of each of the lineages of Monilophytes

The Whisk Ferns

The Ophioglossean ferns

The plant consists of dichotomously

branched rhizomes and upright

dichotomously branched stems.

The Ophioglossean ferns are closely related to the whisk ferns.

However, they have an appearance much more like true ferns.

A major feature is the unusual leaves divided into two segements:

http://www.plantscience4u.com/2014/04/psilotum-sporophyte-plant-

body.html#.Vi5cIrerTcs

https://www2.mcdaniel.edu/Biology/botf99/earlyplants/page3psi.html

The Horsetails

The Horsetails are very common fern-like plants

In the Carboniferous period (about 300

million years ago)

The cross-section of an Equisetum stem

shows a large central cavity surrounded

by several vascular bundles.

Sporangia are borne at the

tips of many stems.

http://www.easttennesseewildflowers.com/galle

ry/index.php/ferns/Copy_of_Horsetails

True Ferns are the major group of Pteridophytes, with over

12,000 described species.

Most true ferns are readily recognized by their complex fronds.

The real distinguishing feature of True Ferns

The leptosporangium has a distinctive stalk and a

covering referred to as an annulus.

Specific terminology is used for the vegetative structures of ferns.

Fern life cycle

Ferns also have an extensive underground portion, the

rhizome, which serves to vegetatively propogate the plant.

Most ferns are homosporous,

producing spores of a single type that

grow into a bisexual gametophyte.

Study outline for Chapter 21b-Early Tracheophytes (Lycophytes and Pteridophytes)

Define tracheophyte.

When did the tracheophytes first appear on dry land?

Describe Rhynia.

Name the evolutionary innovations that occurred in the evolutionary path from bryophytes to lycophytes.

Name the two major extant lineages of the early tracheophytes.

Name the five groups of Lycophytes.

Which groups are extinct?

Which groups are extant?

Lycophytes

Define microphyll.

Define strobilus.

How does Lycopodium differ from a moss?

Lycopodium is __________ (only one type of spore) and Selaginella is _____________ (two different ypes of spores).

Define the following terms and use these terms to label the following life cycles of Selaginella:

microsporangia

megasporangia

microspores

megaspores

strobilus

female gametophyte

(megagametophyte)

male gametophyte

(microgametophyte)

sporophyte

Lycophytes- Label the following: Zosterophyllaphyta; Lycopodium group; Selaginella group; Isoetes; and

Lepidodendrids. List 3 characteristics for each picture.

Pteridophytes

Define megaphyll.

Name the four groups of Pteridophytes that we discussed in class.

Define enation.

Define leptosporangium.

Define the following terms and label the figure.

frond

rachis

pinna

pinnule

fiddlehead

rhizome

Matching-Fern Life Cycle

___ sori

___ archegonium

___ gametophyte

___ leptosporangium

___ zygote

___ antheridium

___ sporophyte

E.

G.

B.

A.

B.

C.

D.

E.

F

G.

Pteridophytes- Label the following: Psilotum (whisk ferns); Ophioglossum ferns; Equisetum (horsetails); and True ferns.

List 3 characteristics for each picture.