Fossils PTERIDOPHYTES

HORNEOPHYTON
CLADOXYLON
FOSSILS FOR MSC STUDENTS, ANATOMY OF HORNEOPHYTON AND CLADOXYLON, REFERENCES

1. MANSI R. MORE
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2. CONTENTS

INTRODUCTION

Horneophyton

Cladoxylon
REFERENCES

REFERENCES
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3. INTRODUCTION

The word fossil is derived from a Latin verb Fodere
which means “to dig”.

Fossils may be precisely defined as “the remains of
ancient plants and animals preserved in the rocks or ancient plants and animals preserved in the rocks or
different layers of earth.”

The branch of science in which we study the plants of
past geological ages through the investigation of
fossils, is called “Palaebotany” .
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4. Horneophyton(Hornealignieri)

Division = Psilophyta

Class = Psilophytopsida

Order = Psilophytales
Family = Rhyniaceae

Family = Rhyniaceae

Genus = Rhynia(Kidston& Lang)

Geographical occurrence = Lower Devonionperiod

Geographical distribution = Mostly reported from
Rhyniachertbed of Scotland.
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5. Characteristic
features
Horneophytonlignieri
was described for the
first time by Kidstonand
Lang (1920) from Rhynie
chertbed as Hornea
lignieri.lignieri.
According to ICBN, the
original generic name
Horneawas previously
occupied by a flowering
plant.
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Horneophyton:-External morphology

6. External morphology

The plant was approximately 6-8 inches (15-20 cm)
high.

The underground portion of the plant consists of a
series of bulbous, corm-like structures bearing series of bulbous, corm-like structures bearing
numerous unicellular rhizoids.

The basal corm lacks any evidence of
vascularizationand is made up of dark, thick-
walled parenchymatouscells.
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7. Anatomy of
H
orneophyton
Internally the
aerial axes have
protostelewith
central placed central placed
protoxylemis
surrounded
externally by
phloem.
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8. Reproductive organ of
Horneophyton
The sporangia are borne externally
at the apex some of the aerial
branches.
Each sporangium is Each sporangium is
dichotomously branched and may
have 2-4 lobes of varying length.
The sporangial lobes are
ellipsoidal cylindrical in shape
with truncated distal end.
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9. Dehiscence of sporangia took place through an
apical pore. Extending into the sporangial cavity is
a column of sterile tissue around which a
continuous layer of sporogenoustissue, composed
of trileteisospores, overarched a central columella.

The sporangium of Horneophytonis unique

The sporangium of Horneophytonis unique
among all vascular plants, because it consists of a
branched fertile unit resulted from dichotomies of
the stem apex.

Moreover, each fertile lobe was produced by its
own apex and remained meristematicfor an
extended period of time.
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10. Classification of Cladoxylon

Class = Cladoxylopsida

Order = Cladoxylales
Family = Cladoxylaceae

Family = Cladoxylaceae

Genus = Cladoxylon

Cladoxylalesis represented by the genus Cladoxylon
with about a dozen species from middle Devonian to
lower Carboniferous.
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11. External
morphology of
Cladoxylon
The stem of Cladoxylon,
upto5 cm in diameter,
was dichotomously
branched and spirally
bore numerous small
(rarely over 2 cm) leaves (rarely over 2 cm) leaves
which were
dichotomously dissected
in one plane and showed
heterophylly.
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Cladoxylon:-External habit

12. Fertile leaves were
borne on some
upper branches.
These
dichotomously dichotomously
dissected and bore
at the tips of the
dissections small
sporangia. They
were homosporous.
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Cladoxylon:-Fertile leaves

13. Anatomy of
Cladoxylon
A T. S. of the stem shows
a broad homogenous
cortex, the central area
of which was polystelic.
The steles were many
and narrow, often and narrow, often
sinuous. They contained
scalariformand pitted
tracheidesand each
stele was surrounded by
a secondary xylem.
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Cladoxylon:-Anatomy of stem

14. References

Pteridophytafor degree students (multicolour edition)

College botany for degree students

www.slideshare.net
www.biologydiscussion.org

www.biologydiscussion.org
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15. THANK YOUTHANK YOU
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