Bonsoir tous
Following my coming across "Psilachnum guttules" in a collection of Lachnum clavigerum on Chamerion angustifolium - http://www.ascofrance.com/search_forum/36237 when I collected a Lachnum on another dead stem of this plant I wanted to see if I could find them again.
To all intents and purposes this second collection was also L. clavigerum: spores right size, asci without croziers, balls of crystals present on tips of hairs. One apothecium had asci with the guttules, another (at a slightly earlier stage of development) apparently did not.
But what surprised me was that a further apothecium I examined showed, in a squash, a perfect ring of golden coloured hairs. I had not noticed any colouration under the stereo microscope, but I wasn't looking for anything other than to remove an apo for examination. Closer observation showed that this colour was produced by numerous golden-coloured acicular crystals covering the distal half of the hairs. Increasing pressure on the coverslip was sufficient for many of them to become free - to start with the hairs were so encrusted as to remind me of an Incrupila. The hairs (ignoring the crystals) were rather more heavily verrucose than the other apo's examined, but otherwise it seemed close to typical L. clavigerum, though there were no globose terminal balls of crystals.
I have struggled to think why a single apothecium should appear so different when in a discrete colony on a single plant stem. I have not examined any more apo's, I am keeping the stem damp to see if any more appear to display this strange appearance.
* All the photographs are of living material mounted in water.   
* The yellow colouration of the crystals is not an artefact - I double checked by examination without Nomarski (therefore no polarisation).
* The crystals were definitely only on the hairs and must have been produced there, no other part of the apothecium showed any such presence, nor was there any evidence of external contamination on the stem itself.
* Annoyingly I had treated the squash with IKI to check apex coloration (BB). In retrospect it would have been interesting to see if any reagents reacted to or removed the crystals. I am hoping that I might find another similar apothecium among the dozens on the stem.

I would be interested to know if others have come across something similar.

amitiés
Chris