The Fascinating World of Hornworts and Mosses

1. Ch 20 Part 2

2. Phylum Anthocerophyta – Hornworts • Structure and form: • Mature sporophytes look like miniature greenish-blackish rods. • Gametophytes thalloid • Cells with only one large chloroplast • Thalli have pores and cavities filled with mucilage that often contain nitrogen-fixing bacteria. • Only about 100 species worldwide • Asexual reproduction by fragmentation of thallus.

3. Phylum Anthocerophyta – Hornworts • Sexual reproduction: • Archegonia and antheridia produced in rows just beneath upper surfaces of gametophytes. • Sporophyte: • With numerous stomata • Meristem above foot continually increases length of sporophyte from base. • Meiosis occurs in sporophyte to produce spores. • Diploid elaters, that function similar to those of liverworts, intermingled with spores.

4. Phylum Bryophyta – Mosses • Structure, form and classes: • About 15,000 species of mosses currently known. • Divided into three classes: • Peat mosses • True mosses • Rock mosses A true moss

5. Phylum Bryophyta – Mosses • Structure, form and classes: • Leaves of moss gametophytes have blades nearly always one-cell thick, except at midrib, and never lobed or divided. • Cells usually contain numerous chloroplasts. • Peat moss leaves have large transparent cells without chloroplasts that absorb water; and small, green, photosynthetic cells sandwiched between. • Axis stemlike, without xylem or phloem. • Often with central strand of hydroids Cells of peat moss leaves

6. Phylum Bryophyta – Mosses • Sexual reproduction: • Gametangia at apices of leafy shoots. • Archegonium cylindrical with egg in swollen base, and neck above containing narrow canal. • Multicellular filaments = paraphyses scattered among archegonia.

7. Phylum Bryophyta – Mosses • Sexual reproduction: • Antheridia on short stalks, surrounded by walls one cell thick. • Sperm cells, each with pair of flagella, formed inside. • Sperm forced out top of antheridium. • Paraphyses scattered among antheridia.

8. Phylum Bryophyta – Mosses • Sexual reproduction: • Archegonia release substances that attract sperm. • Sperm swim down neck of archegonium. • Zygote grows into spindle-shaped embryo. • Top of archegonium splits off and forms cap on top of sporophyte = calyptra. • Mature sporophyte consists of capsule, seta and foot. • Meiosis produces spores inside capsule. • Peristome, composed of one or two rows of teeth, under operculum at tip of capsule. • Peristome opens or closes in response to humidity. • Spores develop into filamentous protonema that produces buds that develop into leafy gametophytes.

9. Phylum Bryophyta – Mosses • Sexual reproduction:

10. Human and Ecological Relevance of Bryophytes • Pioneer species on bare rock after volcanic eruptions or other geological upheavals = succession • Accumulate mineral and organic matter that is utilized by other organisms • Retain moisture, and reduce flooding and erosion • Indicators of surface water • Packing material • Peat mosses most important bryophyte to humans. • Soil conditioner due to high absorptive capacity • Poultice material due to antiseptic properties and absorbency • Fuel