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Fossils PTERIDOPHYTES

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

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MANSI R. MORE 1
CONTENTS  INTRODUCTION  Horneophyton  Cladoxylon REFERENCES REFERENCES 2
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 orancient 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” . 3
Horneophyton (Hornea lignieri)  Division = Psilophyta  Class = Psilophytopsida  Order = Psilophytales Family = Rhyniaceae Family = Rhyniaceae  Genus = Rhynia (Kidston & Lang)  Geographical occurrence = Lower Devonion period  Geographical distribution = Mostly reported from Rhynia chert bed of Scotland. 4
Characteristic features Horneophyton lignieri was described for the first time by Kidston and Lang (1920) from Rhynie chert bed as Hornea lignieri.lignieri. According to ICBN, the original generic name Hornea was previously occupied by a flowering plant. 5 Horneophyton :- External morphology
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 bearingseries of bulbous, corm-like structures bearing numerous unicellular rhizoids.  The basal corm lacks any evidence of vascularization and is made up of dark, thick- walled parenchymatous cells. 6
Anatomy of Horneophyton Internally the aerial axes have protostele with central placedcentral placed protoxylem is surrounded externally by phloem. 7
Reproductive organ of Horneophyton The sporangia are borne externally at the apex some of the aerial branches. Each sporangium isEach 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. 8
 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 sporogenous tissue, composed of trilete isospores, overarched a central columella.  The sporangium of Horneophyton is unique The sporangium of Horneophyton is 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 meristematic for an extended period of time. 9
Classification of Cladoxylon  Class = Cladoxylopsida  Order = Cladoxylales Family = Cladoxylaceae Family = Cladoxylaceae  Genus = Cladoxylon  Cladoxylales is represented by the genus Cladoxylon with about a dozen species from middle Devonian to lower Carboniferous. 10
External morphology of Cladoxylon The stem of Cladoxylon, upto 5 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. 11 Cladoxylon :- External habit
Fertile leaves were borne on some upper branches. These dichotomouslydichotomously dissected and bore at the tips of the dissections small sporangia. They were homosporous. 12 Cladoxylon :- Fertile leaves
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, oftenand narrow, often sinuous. They contained scalariform and pitted tracheides and each stele was surrounded by a secondary xylem. 13 Cladoxylon :- Anatomy of stem
References  Pteridophyta for degree students (multicolour edition)  College botany for degree students  www.slideshare.net www.biologydiscussion.org www.biologydiscussion.org 14
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Fossils PTERIDOPHYTES

  • 2. CONTENTS  INTRODUCTION  Horneophyton  Cladoxylon REFERENCES REFERENCES 2
  • 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 orancient 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” . 3
  • 4. Horneophyton (Hornea lignieri)  Division = Psilophyta  Class = Psilophytopsida  Order = Psilophytales Family = Rhyniaceae Family = Rhyniaceae  Genus = Rhynia (Kidston & Lang)  Geographical occurrence = Lower Devonion period  Geographical distribution = Mostly reported from Rhynia chert bed of Scotland. 4
  • 5. Characteristic features Horneophyton lignieri was described for the first time by Kidston and Lang (1920) from Rhynie chert bed as Hornea lignieri.lignieri. According to ICBN, the original generic name Hornea was previously occupied by a flowering plant. 5 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 bearingseries of bulbous, corm-like structures bearing numerous unicellular rhizoids.  The basal corm lacks any evidence of vascularization and is made up of dark, thick- walled parenchymatous cells. 6
  • 7. Anatomy of Horneophyton Internally the aerial axes have protostele with central placedcentral placed protoxylem is surrounded externally by phloem. 7
  • 8. Reproductive organ of Horneophyton The sporangia are borne externally at the apex some of the aerial branches. Each sporangium isEach 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. 8
  • 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 sporogenous tissue, composed of trilete isospores, overarched a central columella.  The sporangium of Horneophyton is unique The sporangium of Horneophyton is 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 meristematic for an extended period of time. 9
  • 10. Classification of Cladoxylon  Class = Cladoxylopsida  Order = Cladoxylales Family = Cladoxylaceae Family = Cladoxylaceae  Genus = Cladoxylon  Cladoxylales is represented by the genus Cladoxylon with about a dozen species from middle Devonian to lower Carboniferous. 10
  • 11. External morphology of Cladoxylon The stem of Cladoxylon, upto 5 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. 11 Cladoxylon :- External habit
  • 12. Fertile leaves were borne on some upper branches. These dichotomouslydichotomously dissected and bore at the tips of the dissections small sporangia. They were homosporous. 12 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, oftenand narrow, often sinuous. They contained scalariform and pitted tracheides and each stele was surrounded by a secondary xylem. 13 Cladoxylon :- Anatomy of stem
  • 14. References  Pteridophyta for degree students (multicolour edition)  College botany for degree students  www.slideshare.net www.biologydiscussion.org www.biologydiscussion.org 14