Question

Why are the Lycopodiophyta considered the most ancestral vascular plants living today?

Answer 1

Lycopodiophyta belongs to the tracheophyte and are believed to be the most ancestral vascular plants due to following features:

1. Most simple plant body organization

2. All the parts spirally arranged

3. Very simple leaves.

4. Cone is formed terminally on main and lateral branches

5. Cone is made by aggregation of leaves, which loses its chlorophyll and called as Sporophylls

6. Single homosporous sporangium per microsporophyll.

7. Very large number of spores is formed.

8. No heterospory .

9. Spore after germination formed most simple chlorophyllose monoecious gametophyte.

10. Most simple vascular organization, protostele and its variants in the stem of various species.

11. Self fertilization

12. No recombination of new Gene's.

13. Embryo development occurs in the gametophyte.

14. Sporophytes dependent over the gametophyte in an early stage.

15. Very quick life history.

16. Fossil history extends back to devonian or much more early in the paleozoic period

All these characters clearly justify the Lycopodiophyta to be considered as most ancestral vascular plants today.

Baragwanathia longifolia is a most primitive fossil of the group.

If you consider Selaginella, being a heterosporous and leading to go for cross fertilization and with the possibilities for recombination of new Gene's providing the signal towards the process of adaptability to accommodating the genome in the change in an environmental condition for the survival, evolution and creating a chance to forming a new taxa, but at the same time till date most of the features possess by this group of plants are unchanged, archaic from the early paleozoic period.

Some important features can also be added for justification of above statements:

1. Growing near the water (hygrophytic)

2. Simplest organization

3. Simplest vasculature

4. Pigments system like green algae with chlorophyll b

5. Nature of photosynthesis and photosynthesis like green algae.

6. Necessity of external water for the fertilization

7. Presence of a ciliated sperms in an organ at any stage of life (antherozoides).

8. No vessels

9. No secondary growth.