1. Domain Eukarya Kingdom Plantae Phylum Bryophyta
Hornworts
Domain Eukarya
Kingdom Plantae
Phylum Bryophyta

2. Anthoceros: gametophyte thallus with elongating sporophyte
Why is this called a “hornwort?”

3. Anthoceros - the hornwort
The gametophyte is much like a thallose liverwort.
The sporophyte is the horn of the hornwort.
Gametophyte

4. Hornwort Thallus Cross Section
photosynthetic upper epidermis
cortex
lower epidermis
rhizoids

5. Compared to the liverwort thallus, what is missing?

6. Cyanobacteria are often symbionts!

7. What cellular details can you find?

8. The Anthoceros gametophyte thallus has one chloroplast per cell...
Obviously like all other bryophtyes:
chlorophylls a and b
xanthophylls and carotenoids

9. Compared to the liverwort, what is different about the location of the antheridia in hornworts?

10. Antheridium sterile jacket
Spermatogenic tissue
Stalk

11. This Anthoceros gametophyte… shows three antheridia…
Antheridium sterile jacket
Upper Epidermis
Spermatogenic tissue
Thallus parenchyma
Lower Epidermis
Rhizoids

12. Here is the best I could find on the web to show the archegonium which is embedded in the hornwort gametophyte thallus.
Apical Cell
Sterile Jacket Cells
Neck Canal Cells
Ventral Canal Cell
Egg Cell

13. The artist would lose one point above…why?
What are some missing items as well?
The “spore mother cell” is better known as sporocyte!
We shall find out why this is so, as we proceed to more-derived plants.

14. Hornwort sporophyte (with attached gametophyte)
gametophyte “collar”
foot
intercalary meristem
stalk
sporangium

15. Whole mount closeup
What apomorphy is featured here?

16. Longitudinal section

17. The Anthoceros sporophyte foot is embedded in the gametophyte.
The sporophyte seta has an intercalary meristem.
Gametophyte
Thallus
Intercalary
Meristem
Foot
Gametophyte rhizoids

18. The Anthoceros sporophyte has evolved guard cells and stomata.
While initially dependent on the gametophyte, it carries out its own photosynthesis.
The sporophyte may continue to grow while the gametophyte degenerates.
Two apo-morphies are shown here… which?

19. What is this?
How could it be labeled?

20. The Anthoceros sporangium is linear and indeterminate in size.
It is surrounded by a layer of cortex and epidermis.
sterile jacket
sporocyte
The sporocytes divide by meiosis, producing meiospores.
The tri-radiate marks and surfaces that the tetrad of spores impress upon each other are shown here.

21. Hornwort sporangium ls

22. cs, ls, or wm?

23. What would be the labels on this?

28. Here is the cross section of a maturing part of the “horn”…the Anthoceros sporophyte.
The sporophyte shows a cutinized epidermis, a step up from the gametophyte.
In the center of the sporophyte, you can find the hydroids and leptoids!
Spores appear in tetrads (the four meiotic products) of which three are generally in any plane of section
The cortex cells are responsible for the photosynthetic support for the sporophyte.

29. The sporophyte maturing to shed spores to the wind

30. The Anthoceros sporophyte matures from tip to base shedding almost unlimited spores due to intercalary meristem at base.

31. The tip of the Anthoceros sporophyte matures first, shedding the spores to the wind.

32. The Life Cycle of Anthoceros
SYNGAMY
zygote
Sporophyte
Gametophyte
sporangium
sporocyte
spores
gametangia
gametes
germination
mitosis
differentiation 1N 2N
MEIOSIS