HORNWORTS 100 SPECIES

NAMED FOR ITS HORNLIKE SPOROPHYTIC
GENERATION

GAMETOPHYTIC GENERATION DOMINANT

SPOROPHYTE GENERATION IS DEPENDENT ON THE GAMETOPHYTE GENERATION

DIVISION ANTHOCEROTOPHYTA (OR ANTHOCEROPHYTA)

HABITAT: TROPICAL FORESTS, ALONG STREAM SIDES, IN DISTURBED FIELDS, USUALLY ON SOIL BUT CAN BE ON TREE TRUNKS

SIZE AND APPEARANCE: SMALL, GREASY BLUE-GREEN

MORPHOLOGY OF GAMETOPHYTE

GAMETOPHYTE THALLOSE AND GREASY BLUE-GREEN IN COLOR. THE THALLUS IS ORBICULAR OR RIBBON-LIKE AND HAS A MIDLINE

CELLS HAVE A SINGLE LARGE CHLOROPLAST

COMPLETELY ENVELOPING THE NUCLEUS

SPACES BETWEEN CELLS ARE FILLED WITH MUCILAGE RATHER THAN AIR MAKING MUCILAGENOUS CANALS

THE CYANOBACTERIA, NOSTOC, LIVES IN THESE CANALS
      a. NOSTOC FIXES NITROGEN AND PROVIDES IT TO THE
     HORNWORT THALLUS

  b. HORNWORT PROVIDES CARBOHYDRATES TO THE NOSTOC

THIS IS A SYMBIOTIC RELATIONSHIP THAT CAN BE DESCRIBED AS MUTUALISM

THE GAMETANGIA (GAMETE PRODUCING STRUCTURES) ARE PRODUCED ALONG THE THALLUS MIDLINE

a. ARCHEGONIA ARE SUNKEN INTO THE SURFACE OF THE
   THALLUS (EXOGENOUS)

b. ANTHERIDIA ARE LOCATED IN CHAMBERS BENEATH THE
   SURFACE (ENDOGENOUS)

RHIZOIDS ANCHOR THE GAMETOPHYE TO ITS SUBSTRATE

MORPHOLOGY OF THE SPOROPHYTE

THE SPOROPHYTE IS COMPOSED OF A BULBOUS FOOT AND AN ELONGATED CYLINDRICAL SPORE-BEARING REGION.

THE FOOT IS BURIED IN THE GAMETOPHYTE

THE GROWTH OF THE SPORE BEARING REGION IS INDETERMINANT. IT GROWS FROM A MERISTEM JUST ABOVE THE FOOT.

SPORE MATURATION OCCURS FROM THE BASE UPWARD

STOMATES ARE FOUND IN THE EPIDERMAL LAYER OF THE SPOROPHYTE AND ARE THE ONLY EPIDERMAL CELLS TO HAVE CHLOROPLASTS.

A PHOTOSYNTHETIC LAYER IS LOCATED BENEATH THE EPIDERMIS

THE SPORE PRODUCING TISSUE LIES BENEATH THE PHOTOSYNTHETIC LAYER

   a. SPORES ARE ARRANGED AS TETRADS IN THE
      SPOROPHYTE

   b. SPORES ARE SEPARATED AND DISPERSED
      INDIVIDUALLY

SPORE DISPERSAL

THE SPOROPHYTE SPLITS ALONG TWO LONGITUDINAL LINES, STARTING NEAR THE TIP

PSEUDOELATORS HELP DISPERSE THE SPORES

EACH SPORE GIVES RISE TO ONE GAMETOPHYTE