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PHYCOLOGICAL SOCIETY OF AMERICA

Chondracanthus exasperatus morphology

So you've seen a couple pictures by now, but what is C. exasperata really like physically?

 MACROMORPHOLOGY  

                              BLADE         STIPE      HOLDFAST

Blades
    C. exasperatus has large, broad blades, commonly 30-50cm tall and 10-20cm wide.   The blade is a deep red-purple in color.   It is covered in wart-like papillae which vary in size and shape, and it is from these papillae that C. exasperatus gets is common name, Turkish Towel.
    The thallus is erect, foliose, and filamentous.  Juveniles initially have cylindrical thalli, and the apex is rounded.  The adult thalli is also cylindrical, though much more uneven on its edges.  The base begins broadly lanceolate and gradually narrows.  The adult apex can be both continuous or divided.   Growth  is multiaxial at all stages of development and occurs at the apical and marginal meristems (Abbott and Hollenberg, 1976).
    The upright thalli incorporates both the cortex and medulla.  The cortex, or outer part of the thallus, is compact, typically only 6-8 layers thick.  It is composed of branched filaments of spherical or rod shaped cells  These cells are oriented towards the surface and increase in size from the cortex surface towards the medulla.  The medulla, or inner part of the thallus, is thicker than the cortex, and grows secondarily through the transformation of cortical cells to medullary cells.  The cells of the medulla are slender and differentiated, as opposed to the shorter, thicker medullary cells of other Gigartinacae (Ho Kim, 1976).

Stipe
    The stipe is short and cylindrical.   Towards the base of the blade it flattens and flares to about 2-3cm.  It may be branched and give rise to more than one blade.

Holdfast
    The holdfast is relatively small, ranging from a few mm to a few cm in diameter and discoid in shape.  It is composed of cylindrical cells, regularly arranged in rows.  There are commonly 2-3 blades from each holdfast, which may or may not involve a common stipe.  

MICROMORPHOLOGY

Cell Wall:   The microfibrillar framework of C. exasperatus' cell wall is made of cellulose.  The bulk of the cell wall, however, is made of mucilage, specifically carrageenans .

Chloroplasts:    Chloroplasts are discoid in shape and have no endoplasmic recticulum.  There is one thylakoid per band.  The major pigments are chlorophyll a  and d, and the accessory pigments include phycobilins, carotenoids, and phycobiliproteins.

Storage products:     The major storage products is floridean starch which is maintained in the cytoplasm.

Pit Connections:  Pit connections are unique cell connections found in almost all red algae.  They form at cell junctions when apical cells divide to form the filaments of the red alga thallus.  Pit connections can be defined as the opening in the cell wall between two cells which is filled in by a plug and plug cap.   They can form either during cell division, primary pit connections, or between two cells which come to lie near each other, secondary pit connections.   The diagram shows the formation of a primary pit connection.  After the nucleus divides during cell division, the cross wall begins to grow inwards (a), but stops before it completely closes the opening between the two cells (b).  Parallel vesicles line up in this aperture (c) and attract electron-dense material to the opening.  This electron-dense material is surrounded by a membrane to form the "plug" and stabilized on either side by a flattened vesicle, or "plug cap" (d).  Their name is misleading because there really is no connection between the two cells.  Instead, it is hypothesized that pit connections increase the stability of the thallus (Lee, 1980).
 
So I know C. exasperatus'  isomorphic, but is there any way to distinguish a gametophyte blade from a sporophyte blade?

Resorcinol method:  The resorcinol method has been used with success to identify the nonreproductive gametophyte and sporophyte stages of isomorphic red algae.   The procedure involves applying the resorcinol reagent, composed of resorcinol, acetal and HCl, to sections of the blade of a red alga whose life history phase is unknown.  If the reagents remains clear, the section is from a sporophyte, however if it turns red this indicates the section is from a gametophyte.  This test depends on the different amounts and types of carageenan found in the different life history phases of many reds.   In gametophytes, there is typically kappa-carageenan, which reacts with resorcinol to turn it red, whereas sporophytes have primarily  lamba-carageenan, which does not react with resorcinol.
    This method is a reliable test for life history phases in most Iridaea and Rhodoglossum, both in the order Gigartinaceae.  However, studies done with C. exasperatus have shown that it has a slightly different chemical composition which makes the resorcinol test less accurate.   For this alga, both gametophyte and sporophyte blades react with resorcinol to cause a color change.   While the reagent applied to the sporophyte turns more pink than red, the color changes in general are not very consistent making it difficult to distinguish the two reactions from each other, and thus to identify the life history phase.
    Since then, other members of Gigartinaceae have been shown to have variable color reactions to resorcinol.  However, these color variations are still much more consistent within species than are the reactions in C. exasperatus, making it the most frequently misidentified by this method. Identification accuracy has been found to increase with smaller section sizes and increased time periods allowing the color reaction to stabilize, however this method may still be too inconsistent to be relied upon to distinguish C. exasperatus' life history phases (Shaughnessy and Wreede, 1991).

Papillae:    While the morphology of the papillae is not useful in identifying nonreproductive life history phases in C. exasperatus, they can be used to identify reproductive phases.   No studies have been done on how reliable this method is at identifying life history phases, however there are noticeable macroscopic morphological differences between the papillae in male gametophytes, female gametophytes, and sporophytes.

• Male Gametophytes:    The spermatangial papillae have a rounded apex.
• Female Gametophytes:  The cystocarpic papillae also have a broadly rounded apex and are sometimes associated with 3-4 short spines. Microscopic investigation will discover only one cystocarp per papillae.
• Sporophytes:  Tetrasporangial papillae are upwardly decurrent with a sharp apex.  Microscopic investigation will discover that the tetrasporangial sori are subterminal (Abbott and Hollenberg, 1976).

While these distinctions are useful, my investigations of general Chondracanthus papillae found that they were extremely variable among species and thus it was hard to establish an easy set of identifying criteria.  Some examples of the extreme variety in papillae among Chondracanthus are given below, along with whether or not they contained reproductive cystocarps in their papillae.

1)         large view                                

'

part 1                                part 2

papillae without cystocarp               papillae with cystocarp

                             
part 1                                               part 2
 

2)            large view                              papillae with cystocarp             ie. cystocarp
  

3)        large view                                 papillae without cystocarp