here are the requested information according to several authors.
Benkert (Bemerkenswerte Ascomyceten der DDR VI. Die weisssporigen Geoglossaceen. Gleditschia 40:141-171, 1983)
olivaceum : color= brown olivaceous, sometimes with spanish green tinges.stipe= smooth. spores= 13-15. xerophilous places
viride : color=spanish green with ocraceous spot but without brown.stipe=scaly. spores= 16,5-21. wet/hygrophilous places.

JPP's Key 1999 (he will probably answer soon here to give his point of view)
olivaceum: stipe smooth. asci length under 100 µm
viride: stipe squamulose. asci length over 100 µm


Mains (hyaline-spored Geoglosseae Mycologia 47:846-877, 1955)
olivaceum: color=mainly brown to olivaceous. stipe=smooth. spores=(12)14-20(22)x4-5
viride: color=green. stipe usually furfuraceous.spores=10-18(20)x3,5-5

Nordic Macromycetes vol1
viride: color=dark olive green. stipe olive brown, covered with green scale. spors=15-20x5-6, 4-5 septate.paraphyses=slightly pyriform at the apex
olivaceum:color=olive brown, later more green. stipe smooth, glossy, brown or greenish. spores 11-18x4-6, finally 3 septate. paraphyses not enlarged above

in conclusion, I believe that stipe ornementation and spores features shall be more discriminant than general color.
François

Thank you, François for your amicale et rapide reponse.

I've published in"Miscellanea mycologica"( Belgium ) an article about this genius.
I agree with François about ornementation of the stipe and microscopic differences.The color can be different too but all is explain in the article and I can send you by mail a copy to read it.
Sincerely.
Jean-Marc Moingeon.

Thank you, Jean Marc.
I will add a new point of wiew: M. olivaceum has ascus pleurorrinchous < 100 ; M.viride has ascus aporrinchous >100.

I saw this conversation about Microglossum only today. It is right that M. olivaceum has asci consistently arising from croziers and M. viride always from simple septa. Concerning ascus measurements one must know that Benkert mesured the ascus length in dead material. Therefore he found olivaceum to be shorter than 100 µm. But when the asci are alive, they are much much longer: 137-200 in viride and 83-144 in olivaceum (see my key on DVD).
with best regards
Zotto

Buongiorno al Forum,
sto' studiando alcuni esemplari che probabilmente sono da ricondurre a M. olivaceum e mi sono sorti dei dubbi in merito.
Qualcuno mi saprebbe dire se Microglossum nudipes è una buona specie oppure è stata sinonimizzata con qualche altra?
Io non trovo alcuna descrizione di M. nudipes, oltre a quella in Grelet1979.

Senza voler intasare il forum con troppe foto, appena possibile posterò il lavoro completo nel forum di Muggia.

Vi ringrazio in anticipo.
Ciao,
Marino Zugna

"olivaceum : xerophilous places
viride : wet/hygrophilous places."

So wouldn't the ecology be a good way to separate both species as well, and this before verifying with microscopy?