FERNS

   PTEROPSIDA

DEFINING FEATURES

1. LARGE LEAVES
2. LEAF GAPS

- WHERE THE LEAF TRACE LEAVES THE VASCULAR SYSTEM OF THE STEM

3. DEVELOPMENT OF SPORANGIA ON SPECIALIZED LEAF SEGMENTS

FROND (LEAF)

1. MOST CONSPICUOUS PART OF A FERN PLANT (SPOROPHYTE)
2. VERY VARIABLE
3. LEAF MARGINS MAY BE ENTIRE OR HIGHLY DISSECTED INTO
        LEAFLETS (PINNAE)
4. ARISE FROM RHIZOMES UNDERGROUND OR FROM ERECT STEMS
        a. CELLS ON ADAXIAL (TOP)SIDE OF THE LEAF ENLARGE FASTER THAN
      CELLS ON THE ABAXIAL (BACK)SIDE OF THE LEAF MAKING
A
     
FIDDLEHEAD
        b. FIDDLEHEAD UNCOILS WHEN CELLS ON THE ABAXIAL SIDE START TO
      ENLARGE MORE THAN ON THE ADAXIAL SURFACE
THE COILING AND
      UNCOILING PROCESS IS TERMED,
CIRCINATE VERNATION

SPORANGIA FORMATION

1. DEVELOPE EMBEDDED IN MODIFIED LEAF SEGMENTS AND/OR ON MARGINS
   AND ABAXIAL SURFACES OF LEAVES

2. OFTEN GROUPED IN SORI

SORI - PLEURAL
SORUS - SINGULAR
SOROS = A HEAP

3. SORUS PROTECTED BY AN INDUSIUM
       a. AN INDUSIUM IS AN OUTGROWTH OF THE LEAF SURFACE
       b. A FALSE INDUSIUM IS WHEN THE EDGE OF THE LEAF
              INFOLDS THE SORUS
       c. POSITION OF THE SORI IS AN IMPORTANT CLASSIFICATION TOOL

FERN LIFE CYCLE

THE GAMETOPHYTE (PROTHALLUS) IS:

1. SHORT-LIVED
2. PHOTOSYNTHETIC
3. HEART-SHAPED
4. SMALL (1-2.5 CM)
5. ANCHORED TO SUBSTRATE BY COLORLESS, UNICELLULAR RHIZOIDS
6. BEARS BOTH ANTHERIDIA AND
ARCHEGONIA
       a. ARCHEGONIA NEAR THE POINT
       b. ARCHEGONIA NEAR THE NOTCH

SPORANGIUM DEVELOPMENT

1. EUSPORANGIATE - SPORANGIA ARISE FROM MORE THAN ONE CELL
       ON THE LEAF SURFACE
       a. ARE RELATIVELY LARGE
       b. HAVE MASSIVE STALKS OR NO STALKS
       c. CONTAIN MANY SPORES

2. LEPTOSPORANGIATE (COMMONEST)
        a. ARISE FROM A SINGLE LEAF SURFACE CELL
        b. RELATIVELY SMALL
        c. HAVE A DELICATE STALK
        d. SMALL NUMBER OF SPORES IN MULTIPLES OF 4

SPORE DISPERSAL

SPORES ARE FLUNG FROM THE SPORANGIUM

1. SPORANGIUM SURROUNDED BY AN INCOMPLETE RING OF CELLS CALLED AN
  
ANNULUS
2. THIN OUTER WALLS OF THE ANNULUS SLOWLY CONTRACT AS THEY DRY
3. A PULLING FORCE IS CREATED THAT RUPTURES THE SPORANGIA
        WALL
4. THE TENSION IN THE ANNULUS CELLS INCREASES AS WATER EVAPORATES
5. WHEN ALL WATER EVAPORATES, THE TENSION IS RELEASED AND THE
       ANNULUS SNAPS BACK TO ITS ORIGINAL POSITION EJECTING THE
       SPORES UP TO 1 CM

MOST FERNS ARE HOMOSPOROUS

HETEROSPOROUS FERNS ARE MAINLY AQUATIC