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Uromyces like fungus on Euphorbia peplus (and E. exigua) causing hypertrophy.
Stephen Martin Mifsud, 28-01-2025 11:36
Stephen Martin MifsudHello, I have found plants of Euphorbia peplus and E. exigua infected with a rust which I believe it is Melampsora euphorbiae (confirmation would be kindly appreciated). I was amazed because it caused some hypertrophy on the host plants, namely more suculent leaves and stem, and leaves getting more separated and distant from each other. I do not know how common is this because the images I see on the net of the host plants with this fungus do not show a great deal of hypertrophy.

The crater-like openings in the epidermis of the leaves are stunning under the microscope :-)

[EDIT]:
It was suggested that this corresponds better to Uromyces sp. due to the presence of aecia with pseudoperidium (Caeoma-aecia) that Melampsora euphorbiae usally lacks. See replies below.
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Lothar Krieglsteiner, 28-01-2025 11:44
Lothar Krieglsteiner
definitely no Melampsora euphorbiae causing hypertrophy
Melampsora-rusts have Caeoma-aecia, aecia without pseudoperidium. Your aecia clearly show the white pseudoperidium. So I would look in the genus Uromyces.
Lothar Krieglsteiner, 28-01-2025 11:46
Lothar Krieglsteiner
Re : Melampsora euphorbiae causing hypertrophy
and by the way: hypertrophies are typical in Uromyces, for instance U. pisi (pisi-sativi) on Euphorbia cyparissias.
Björn Sothmann, 28-01-2025 11:47
Björn Sothmann
Re : Melampsora euphorbiae causing hypertrophy
Hi Stephen,

ut is definitely not M. euphorbiae which does not form aecia but only uredia and telia. On E. exigua, there is Uromyces tuberculosus forming aecia, but according to Gäumann, plants infected with aecia of U. tuberculosus should not be deformed. You can try to keep observing the plant. If it is U. tuberculatus, it should also form brownish uredia and telia later on.

Best,

Björn
Lothar Krieglsteiner, 28-01-2025 11:55
Lothar Krieglsteiner
Re : Melampsora euphorbiae causing hypertrophy
Hello Björn,

no - Melampsora euphorbiae forms aecia (Caeoma type), the autoecical rust forms all 4(5) develompment stages on one host - compare for instance:

https://www.phytoparasiten.de/melampsora-euphorbiae-4/

Regards, Lothar
Björn Sothmann, 28-01-2025 12:08
Björn Sothmann
Re : Melampsora euphorbiae causing hypertrophy
Hi Lothar,

yes you are right (though in practice one rarely ever observes these caeoma type aecia on Euphorbia). Interestingly, Julia Kruse also mentions Aecidium euphorbia on E. exigua from Greece on her homepage. That would fit well with hyperthrophied plants that Stephen found. So I guess one really needs to keep observing the infected plants.

Best,

Björn
Lothar Krieglsteiner, 28-01-2025 12:11
Lothar Krieglsteiner
Re : Melampsora euphorbiae causing hypertrophy
indeed, the caeomata and the uredinia look quite similar in autoecical rusts besides Puccinia and Uromyces (Phragmidium the same) so you are surely right that in practice you can ignore them.
Stephen Martin Mifsud, 28-01-2025 12:13
Stephen Martin Mifsud
Re : Melampsora euphorbiae causing hypertrophy
Dear friends - that was quick response! I was carried away with the name M. euphorbiae and did not look further options!

I will correct the title. I got a suggestion by Fabian Ernst of Uromyces tuberculosus which is cited to grow on E. peplus and E. exigua. I will seek further knowledge, but it is nice to learn new stuff here :-)

THANKS/ 

Stephen Martin Mifsud, 28-01-2025 12:35
Stephen Martin Mifsud
Re : Uromyces like fungus on Euphorbia peplus (and E. exigua) causing hypertrophy.
Hi Bjorn, Aecidium euphorbia is matching really well.

e.g. 
https://bladmineerders.nl/parasites/fungi/dikarya/basidiomycota/pucciniomycotina/pucciniomycetes/pucciniales/pucciniales-incertae-sedis/aecidium/aecidium-euphorbiae/

I have an uprooted plant and two more, I will follow up. One of the plants is in its advanced state of infection so I will investigate further later on. 


Stephen Martin Mifsud, 28-01-2025 21:47
Stephen Martin Mifsud
Re : Uromyces like fungus on Euphorbia peplus (and E. exigua) causing hypertrophy.
So I did some further investgations and along my collected specimen I found a pustule with dark-brown spores which under the microscope seems to be shortly-pedicellate, warted teliospores. I found only one pustule and the teliospores matches with Uromyces tuberculatus.

From what I read and learnt today, this would make my fungus Uromyces tuberculatus on the principle that Aecidium lacks completely the teliospore formation in its life cycle whereas U. tuberculatus grows specifically on E. exigua and forms verrucose teliospores.


However reading the host reaction (galling) of Aecidium euphorbiae on Euphorbia exigua, the symptms match perfectly to what I saw, thickened stems and leaves, erect growth, hypertrophy. Then, the same source (weblink above) says that U. tuberculatus rarely (does not) effects the host.


This makes things confusing, so unless we have double infection by two rust fungi (I think we can eliminate this possibility) the options are:


1. Uromyces tuberculatus but making an abnormal hypertropic reaction of the host OR
2. Aecidum euphorbiae but exceptionally is making teliospores on my sample.


I dont know what to choose between the two evils but 1 would be more realistic.

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Björn Sothmann, 29-01-2025 06:39
Björn Sothmann
Re : Uromyces like fungus on Euphorbia peplus (and E. exigua) causing hypertrophy.
The teliospores match Uromyces tuberculatus perfectly, see e.g. Gäumann Die Rostpilze Mitteleuropas p. 324 (online here: https://www.e-periodica.ch/digbib/view?pid=cry-001%3A1959%3A12%3A%3A17#17). So I guess that plants infected by U. tuberculatus can also get deformed.
Stephen Martin Mifsud, 29-01-2025 17:39
Stephen Martin Mifsud
Re : Uromyces like fungus on Euphorbia peplus (and E. exigua) causing hypertrophy.
Björn and Lothar many thanks for writing your feedback and making me wiser about the world of rusts! 

Yes we can conclude that this is Uromyces tuberculatus and that IT EFFECTS the host as explained above. 

Great!