Mosses

Gametophyte (=gamete-forming) phase

Vegetative features

• The gametophyte is green, leafy, multicellular, and mostly macroscopic

• The gametophyte stage starts when spores germinate 

  • These spores produce algae-like, filamentous strands called protonema

  • These protonema strands will eventually create buds that grow into a leafy moss

Stems

• Moss stems can be upright or creeping, and these forms can help identify mosses

  • Upright mosses are called acrocarpous

  • Creeping or prostrate mosses are called pleurocarpous

• Even though mosses are non-vascular, some can have water-conducting cells called hydroids, and sugar-conducting cells called leptoids

  • These cells are found in both gametophyte and sporophyte of taller acrocarpic mosses

  • Hydroid cells are not true xylem, because they lack lignin

Leaves

• Mosses have spirally-arranged leaves

  • These leaves are arranged 360 degrees around the stem (compare to leafy liverworts which have their leaves in two rows)

• Moss leaves are sometimes called "phyllids", to differentiate them from leaves in vascular plants

"Roots"

• Mosses lack true roots, but possess root-like rhizoids

• These rhizoids anchor the plant, but do not contribute much to water absorption

• Moss rhizoids are multicellular and brown (compare to the unicellular and clear rhizoids of liverworts)

Reproductive features

Sexual reproduction

• Sperm- and egg-forming structures (=gametangia) grow in special clusters at tips of plant, sometimes called splash cups

• Sperm (=male gamete), produced in antheridium, swim through water to the female (see image below)

• An egg (=female gamete) is produced in the archegonium on a female gametophyte (see image below)

• Sperm swim to and into the archegonium and fertilizes the egg, although there is some evidence that tiny arthropods may assist in fertilization

• The result is an embryo, which is a young sporophyte, starts to grow off the tip of this female gametophyte 

Diversity

• The most species-rich group of bryophytes (~12,000 spp.) 

Takakiopsida

• 1 order, 1 family, 1 genus (Takakia), 2 species (T. ceratophylla; T. lepidozioides)

• Native to western North America and central and eastern Asia

• Takakia has one of the lowest known chromosome count (n=4) per cell

Sphagnopsida

• 1 extant order, 3 families (Ambuchananiaceae, Flatbergiaceae, Sphagnaceae), 4 genera (Ambuchanania, Eosphagnum, Flatbergium, and Sphagnum), 200 species

• Peat Mosses: mosses that store water and secrete acid in bogs  

• Sphagnum possesses hyaline cells in their leaves that store water.

Andreaeopsida

• Granite Mosses: grow on rocky habitats ranging from tropical to arctic climates, on which they form tufted colonies, typically with reddish to blackish shoots

• 1 extant order, 1 family, 2 genera (Acroschisma, Andreaea), 100 species

Andreaeobryopsida

• Endemic to Alaska and western Canada

• 1 order, 1 family, 1 species (Andreaeobryum macrosporum)

Oedipodiopsida

• Distributed in cooler climates of Eurasia, as well as from Alaska, Washington state, British Columbia, Yukon, Greenland, Newfoundland, Tierra del Fuego and the Falkland Islands

• 1 order, 1 family, 1 species (Oedipodium griffithianum)

Polytrichopsida

• Nematodontous or Hair-cap Mosses

• 1 order, 1 family, 20 genera (Alophosia, Atrichopsis, Atrichum, Bartramiopsis, Dawsonia, Dendroligotrichum, Hebantia, Itatiella, Lyellia, Meiotrichum, Notoligotrichum, Oligotrichum, Plagioracelopus, Pogonatum, Polytrichadelphus, Polytrichastrum, Polytrichum, Pseudatrichum, Psilopilum, Steereobryon)

Tetraphidopsida

• Commonly found in northern latitudes

• 1 order, 1 family, 2 genera (Tetraphis and Tetrodontium), 4 species (Tetraphis - T. geniculata and T. pellucida; Tetrodontium - T. brownianum and T. repandum)

Bryopsida

• True or Arthrodontous or Jointed-toothed Mosses

• 24 orders, 103 families, 11,500 species