Observation 15682: Hypoxylon fragiforme (Pers.) J. Kickx f.
When: 2008-12-23
No herbarium specimen

Notes: What could this be?

The black spherical fungus seems to me to be Hypoxylon fragiforme found on dead branches of Fagus sylvatica. But what could these small red ‘dots’ be? They don’t move and are firmly tightened to the underlying fungus. Another fungus parasitizing the black one? Any hint would be appreciated very much.

Amadej Trnkoczy

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Thanks for explaining
By: Irene Andersson (irenea)
2008-12-27 17:32:22 CST (-0500)

Now I understand (just not used to such advanced camera equipment..).

That measured size of object
By: amadej trnkoczy (amadej)
2008-12-27 16:57:57 CST (-0500)

Dear Irene,

Thanks for your comment. You are right that the size of a picture of an object (at sensor/film plane) generally depends on the distance between the lens and the object.

Yet, this fact doesn’t apply for macro work at a given magnification ratio, say, 1:1. At 1:1 magnification ratio an object (assuming its picture is sharp) must be twice a focal length of the lens away of the lens plane (that is 210 mm for my Nikorr Micro 105 mm/ f 2.8 lens). At the same time the distance between lens plane and sensor/film plane must be the same. Thus, for a sharp picture, the distance between an object and sensor/film plane must be four times the focal length of the lens (420 mm in my case). In practice small departures from this rule are possible due to allowed depth of field. Unfortunately, the depth of field is very very small, only a few mm, at such high magnification. Consequently the only applicable distances between an object and sensor/film plane is 420 mm plus or minus a few mm. Everything which is closer or further away is heavily blurred and mostly unrecognizable.

This is the reason why, at 1:1 magnification ratio, every sharp picture of an objects has almost exactly the same dimension as the object itself. A possible error due to the depth of field issue is negligible for most practical purposes. From here on, that is considering physical size of digital sensor/film and eventual cropping of the picture, it is not difficult to generate a ruler.

In practical field work I always take at least one picture of every (sufficiently small) object at 1:1 magnification ratio just to keep track of its dimension. I adjust my macro lens to the closest focus possible (assuring 1:1 ratio) and sharpen the object using macro-focusing-rails (not by rotating sharpening/distance ring of my lens or using auto focus!). In this way I always have sufficiently well documented objects’ dimensions.

Thank you again for your ID. Since I am a mushroom idiot, I would probably never found out what these ‘red dots’ are without your good will.

All the best in 2009 and
Warmest regards

That measured size of the object
By: Irene Andersson (irenea)
2008-12-25 09:09:09 CST (-0500)

would be different if the distance between the object and the lens is zero, two, or five centimeters, wouldn’t it?
This shot must have been very close though, because the size of the perithecia looks about right compared to the ruler.

(I don’t doubt that Californian fragiforme are ten times bigger, we all know that everything is bigger in USA :-)

I don’t know any other reliable way to tell fragiforme and howeianum apart, than the size of the spores – but on Fagus, it’s most likely fragiforme.

Forgoten info
By: amadej trnkoczy (amadej)
2008-12-25 04:32:35 CST (-0500)

In explaining how I got the 3 mm scale on the picture I forgot to say that the picture was taken by Nikorr Micro 105/2.8 lens at 1:1 magnification. That means that the size of the object and its picture on camera’s sensor are of the same size. Sorry for that.

Thanks, stomata diameter
By: amadej trnkoczy (amadej)
2008-12-24 09:13:11 CST (-0500)

Thanks Irene and Darvin,

With respect to the Hypoxylon fragiforme I admit I am not sure the determination is correct. I am only a mushroom beginner with little experience and knowledge having no microscope. Nevertheless, the size seems to me small too. However, stomata diameter of H. fragiforme I’ve found on the net goes from 1 mm to 16 mm (details below). May be, the species photographed still fits?

3 mm measure is much more reliable. The pictures are taken with Nikon D70 having 14.8 mm high digital sensor and the original picture is cropped to about 2/3. So, it is not too difficult to ‘generate’ a reasonably accurate measure.

Thank you very much again for your comments.


Stomata diameters at:
2-9 mm diameter,
http://mycology.sinica.edu.tw/... 2-13 mm diameter,

http://www.messiah.edu/... 3-16 mm diameter,

http://www.rogersmushrooms.com/... 1-10 mm diameter.

Very small
By: Darvin DeShazer (darv)
2008-12-23 23:08:46 CST (-0500)

If the 3 mm bar is accurate, these are very small Hypoxylons! They are about 1/10 the size we normally see for this genus in California.

Nectria episphaeria
By: Irene Andersson (irenea)
2008-12-23 18:34:18 CST (-0500)

is the most common one on pyrenomycetes (i think..)

Created: 2008-12-23 13:54:17 CST (-0500)
Last modified: 2016-01-12 03:19:41 CST (-0500)
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