Spores - THE definative taxonomic feature??

Steven Carpenter microbe at PEAK.ORG
Thu Feb 22 09:23:14 EST 1996


The idea of spore size and shape being the final piece of information was 
determined by taxonomist(s) working on the groups.  If nobody has 
completed a comprehensive monograph, where type specimens and other 
collections from all around the world were examined, then it is likely 
that true variation in the genus has not been studied very well, 
including at the spore level.

Usually, when making a species determination, there are a lot of other
features in some key or sets of descriptions that you have winnowed
through, so that by the time you have gotten down to two or three species
to compare, you may be left with only a couple of characters that
differentiate the species (at least on paper).  Whether the species
actually ARE different is a taxonomic JUDGEMENT that you are left with. 
You are not obligated to accept the judgement of the monographer or
taxonomist if you have other information that tells you that a different
judgement from your perspective is in order. That concept doesn't leave 
everyone with a particularly warm feeling, but that is the nature of 
alpha-taxonomy.  And, too, molecular work gives more taxonomic characters 
upon which a judgement is required - and it may be that molecular 
characters correlate with spore size and shape, so all you may be left 
with is just what you have today.  

Additionally, there is the "ecotype" concept which has been curiously 
avoided by mycologists.  Clausen, Keck and Heisey (sp?) did some 
groundbreaking work on the effect of environment on plant growth with 
Achillea in California in the late 1940's.  By cross-planting collections 
from their original environment, say on a high mountain, to a different 
environment, say a coastal plain, they discovered that genetic drift 
resulted in phenotypic responses (such as flowering time, leaf thickness) 
that remained constant regardless of environment (high mountain 
collections continued to flower late in the summer even though they were 
planted in the coastal plain, and coastal plain plants transplanted to 
high locations flowered early).  The same is likely true for the fungi, 
it is just that precious little has been done on this subject.  Some of 
us who have worked in the tropics have noted an amazing change in spore 
volume of the same species from sea-level to 4000 meters (see Dennis' 
introduction to "Fungus Flora of Venezuela").  

Anyway, your question brings up an important point, and shows that
Mycology requires greater depth of taxonomic research than was previously
sought.  We can only understand so much from herbarium material (although
label data DOES carry validity as to time of year, longitude & latitude,
etc for ecological considerations) and it is clear that even
alpha-taxonomy could benefit from the kind of work that CK&H did in
California. 

My $.02

-Steven E. Carpenter
 Cascade Research Associates
  & Abbey Lane Laboratory
 microbe at peak.org

R.N. Weinstein (rnw1001 at cus.cam.ac.uk) wrote:
: What do you all think?:

: Is there a consensus that spore SIZE, within a range, and spore SHAPE is 
: enough to be the last word in species identification?  This seems to be the 
: current state of affairs in fungal taxonomy.  Is this system a relic, or 
: is it perhaps just a matter of it being the best system around by default?

: I have isolated a fungus from Antarctic soils which was initially identified 
: to genus Humicola.  This fungus appears to be truly psychrophilic, 
: growing so far at temps as low as -2 C but not at temps above 20 C.  
: Submitted for a more precise identification, it was identified as Humicola 
: fuscoatra.

: We then obtained a culture of H.fuscoatra and found that its 
: temperature/growth range was the opposite of my isolate: it did not grow 
: at +5 C, but grew robustly at 25 C.  Its growth FORM (in a petri dish) 
: was very different from mine: H. fuscoatra was white and fluffy (lots 
: of aerial mycelium); mine dark and swirly growing into the agar.

: However, according to the institute doing the identification, it all 
: comes down to spore size and shape.  And so, without using molecular 
: techniques and doing a thesis's amount of work to prove a difference in 
: species, this appears to be the answer I must settle for.

: Does this seem right?  Opinions please!


: Rick Weinstein
: University of Cambridge



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