origin of Gymnosperms.pptx

Ppt (Origin of Gymnosperms )

1. Origin of Gymnosperms Lalita Roll no. 1211331030016 B.Sc. Medical (2 nd year)

2. Content Introduction Evolution Monophyletic origin Progymnosperms Pteridospermiales Cordaitales Gnetales

3. Gymnosperms are originated about 319 million years ago in the late carboniferous. They are the first seed plants to have evolved. The earliest seedlike bodies are found in rocks of the Upper Devonian series It is a diverse cluster off plants containing cycads,ginkgos amd shrubs. Introduction

4. Evolution Of Gymnosperms Gymnosperms are believed to have evolve d from the paleozoic to the Mesozoic eras. Origin can be traced back by studying their fossil records. Fossil study of “ progymnosperms ” was done.(group created by C.B. Beck which includes all primitive fossil plants) It revealed that plants existing during Devonian period possessed pteridophytic chrs . and by the upper Devonion , acquired gymnospermic chrs . Philips,Rothwell and Erwin also supported Beck for the group progymnosperms to be the possible ancestor of Gymnosperms.

5. Monophyletic Origin of Gymnosperms -supported by Beck(1976) A. B. 1. 2. 1. 2.

6. Progymnosperms ♧ Two lines of evolution arose from them which led to the origin of 2 groups: A. Pteridospermales ( Cyadofillicales ) B. Cordaitales ( the conifer like plants) Both of these groups flourished well in Palaeozoic era and possessed drastic similarity in the str of seed. But origin of Cordaitales presents 2 alternatives as they retained less ancient features than Pteridospermales . These are: ( i ) They arose differently from the same ancestral stock. (ii) They were differentiated from Pteridospermales very early.

7. A. From Pteridospermales , Arose two Mesozoic groups: 1.Cycadales 2. Cycadeoidales ( Bennettitales ) Both of these groups evolved parallel. lThey are considered as distinct groups as they differ from each other in 2 major characteristics: ( i ) Cone structure (ii) ontogeny of stomata In the two, Cycadeoidales occupy terminal position in the line of gymnosperm evolution. Due to presence of peculiar bisexual flower like strobili,considered as fore runners of the present day angiosperms.

8. Both groups show significant similarities with the most primitive Pteridospermales (e.g. Lyginopteris amd Medullosa ) , fr om which they arose . ♡ Similarities in Cycadales : Pinnate foliage,armoir of persistent leaf bases. Large pith and cortex with mucilage canals. Similarity in steel. Loosely arranged female cones. Motile and ciliated sperms. ♡ Similarities in Cycadeoidales : Growth habit similar to Lyginopteridaceae . Similar anatomy. Presence of dyndetocheilic type of stomata as in the members of family Medullosaceae .

9. B. From Cordaitales , Two Mesozoic groups : 1. Ginkgoales 2. Coniferales Ginkgoales were never a large group. It retained certain primitive characters which were not retained by Coniferales . These chrs also present in Cycads but the group is not direct connected with them. Group Ginkgoales possessed certain advanced chrs which were also present in Coniferales . 1. GINKGOALES:

10. ♡ Primitive characters in Ginkgoales : Str of seed and ovule. Presence of motile sperms. Mode of fertilization. ♡ Advanced characters of Conifers in Ginkgoales : Lofty and branched habit. Stem str anf vascular anatomy. Ovulate strobili. ♡ Peculiar Characters of Ginkgoales : Foliage characteristics. Str of strobili.

11. 2. CONIFERALES They began the extensive differentiation during the Mesozoic and resulted in the formation of recognizable tribes of present day flora. Among these, the earliest to be recognized are : Abietinae and Araucariaceae . ● Voltziales are regarded as “ Transitional Conifers ” btw Cordaitales and Coniferales . They were in existence before the Cordaitales became extinct.

12. Gnetales These have not been discovered as fossils . Among Gnetales , the genus Ephedra show more closer characteristics to Gymnosperms than the other 2 genera i.e. Gnetum and Welwitschia . This group possesses angiosperms features. They may have a common ancestory , maybe from a hypothetical group and the two have developed parallel .

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