Re: [OGD] Are orchids parasites?

[marianne.fleurimont]

Hello Sandy,

From various sources (online and in books) I have come to understand the
following:

1) Most orchids need fungus to germinate.  This is a fight of life and
death.  If the fungus is too strong, it can kill the seed.  If the seed can
keep the fungus in check, it survives and grows.

2) From germination, an orchid seed relies on the fungus for nutrition.
This period can be long or short, depending on genera and species.  Phals
quickly put out leaves and can flower in about 4 years.  Some slipper
orchids could take many years before putting up a leaf, and many more before
flowering.  Also, there exist orchids who are not able to make chlorophyl at
all, and rely 100% on fungus to feed them.  Upon maturity, some orchids tend
to eliminate fungii from their roots.  Others tend to keep a colony handy.

3) Even orchids who have green leaves and produce food by photosynthesis can
revert to their earlier phase of fungal dependency should conditions force
them into prolonged dormancy underground.  If the orchid had eliminated all
fungii from its roots, it can always invite a new colonization.  So, in
bad conditions, some orchids will simply go underground and live off of
fungus until it feels conditions have ameliorated above, and will put out
new leaves and flowers.  This is especially true of terestrial species with
tubers.  Epiphytes might function somewhat differently.

(I got most of my information out of books on European native orchids.  Some
websites are cited in the following links on symbiosis between fungus and
orchids).

Sincerely,

Marianne

To see some disscussions and links:

http://ukorchidforum.proboards24.com/index.cgi?board=orchidchataction=displaynum=1090921407

http://ukorchidforum.proboards24.com/index.cgi?board=orchidchataction=displaynum=1093603565
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Re: [OGD] Are orchids parasites?

[Paul J. Johnson]

Ms. Gillians,
   The context in which the reporter used the term parasitic is not, 
in my mind, a contradiction, but rather an indication that she knows 
little, and understands poorly, of what she writes.

A parasite is a living organism that takes nutrients from another 
living organism and generally permits the host to survive, often 
through multiple generations of the parasite.  The news article (which 
was read in its entirety) seems to refer to the orchid taking nutrients 
from fungal tissue killed by the host.  This is not parasitism, 
strictly speaking.  In zoology, there is a fine discrimination between 
so-called true parasites and parasitoids, the later killing the host as 
a consequence it completing its life cycle.  In botany, there is even a 
finer line between parasites and their hosts, usually taking the form 
of symbioses or mutualisms; this is the relationship of some orchids 
with some fungi, but apparently not all nor always.  To confuse matters 
even more, what may start, or appear to start as a parasitic 
relationship does not necessarily remain, but may become a symbiotic 
relationship, or a reversed predatory role.  In recently reported 
research there is evidence suggesting that the question of whether a 
fungus or the orchid are parasites upon each other is challenged, 
reducing traditional thoughts to semantic arguments as the biological 
realities of orchids in the real world (i.e., outside of our 
collections!) become better known.  The concept of predation of one 
plant upon another, or upon a fungus or another organism, is a 
non-traditional perspective and begets additional semantic problems.  
The difference between parasitism (or parasitoidism) and predation, 
too, is a fine distinction.

Paul
Paul J. Johnson, Ph.D.
Professor of Entomology
Insect Research Collection
Box 2207A, South Dakota State University
Brookings, SD 57007-0001
tel: 605.688.4438; fax: 605.688.4602
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