Domain Eukarya Kingdom Plantae Phylum Bryophyta Hornworts Domain Eukarya Kingdom Plantae Phylum Bryophyta

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

Anthoceros - the hornwort The gametophyte is much like a thallose liverwort. The sporophyte is the horn of the hornwort. Gametophyte http://botit.botany.wisc.edu/images/130/Bryophytes/Anthocerophyta/Anthoceros.jpg

Hornwort Thallus Cross Section photosynthetic upper epidermis cortex lower epidermis rhizoids

Compared to the liverwort thallus, what is missing?

Cyanobacteria are often symbionts!

What cellular details can you find?

The Anthoceros gametophyte thallus has one chloroplast per cell... Obviously like all other bryophtyes: chlorophylls a and b xanthophylls and carotenoids http://botit.botany.wisc.edu/images/130/Bryophytes/Anthocerophyta/Pyrenoids_MC.low.jpg

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

Antheridium sterile jacket Spermatogenic tissue Stalk

This Anthoceros gametophyte… shows three antheridia… Antheridium sterile jacket Upper Epidermis Spermatogenic tissue Thallus parenchyma Lower Epidermis Rhizoids http://www.dipbot.unict.it/sistematica_es/Immagini/18002.JPG

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 http://www.science.siu.edu/landplants/Anthocerophyta/images/Phaeoc.laevis.arch.JPEG Ventral Canal Cell Egg Cell

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.

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

Whole mount closeup What apomorphy is featured here?

Longitudinal section

The Anthoceros sporophyte foot is embedded in the gametophyte. The sporophyte seta has an intercalary meristem. Gametophyte Thallus Intercalary Meristem Foot Gametophyte rhizoids http://botit.botany.wisc.edu/images/130/Bryophytes/Anthocerophyta/Sporophyte_foot_MC.jpg

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. http://www.personal.psu.edu/faculty/t/r/trp2/anthoceros.jpeg Two apo-morphies are shown here… which? http://botit.botany.wisc.edu/images/130/Bryophytes/Anthocerophyta/stomata.jpg

What is this? How could it be labeled?

The Anthoceros sporangium is linear and indeterminate in size. It is surrounded by a layer of cortex and epidermis. http://www.puc.edu/Faculty/Gilbert_Muth/phot0123.jpg 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. http://www.biology.lsa.umich.edu/courses/bio255/antho2.jpg

Hornwort sporangium ls

cs, ls, or wm?

What would be the labels on this?

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. http://www.biology.lsa.umich.edu/courses/bio255/antho.jpg

The sporophyte maturing to shed spores to the wind

The Anthoceros sporophyte matures from tip to base shedding almost unlimited spores due to intercalary meristem at base. http://botit.botany.wisc.edu/images/130/Bryophytes/Anthocerophyta/Sporophytes_lg_DH_.jpg

The tip of the Anthoceros sporophyte matures first, shedding the spores to the wind. http://www.hiddenforest.co.nz/bryophytes/hornworts/anthocertaceae/images/horn03.jpg

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