Melampsora populnea (Persoon) Karsten, 1879
on Larix, Pinus Papaveraceae
gall
Aecia 1 mm, often confluent, yellow-orange, without a peridium.
spermogonia, aecia
Euphorbiaceae, Papaveraceae, Pinaceae, polyphagous
Chelidonium majus; Corydalis cava & subsp. marschalliana, intermedia, solida; Larix decidua, kaempferi, sibirica; Mercurialis annua, perennis; Papaver dubium; Pinus brutia, halpenenis, mugo, nigra & subsp. laricio, pinaster, sylvestris.
on Populus

Populus tremula (sucker), Bergen aan Zee; uredinia

Populus tremula, België, prov. Limburg, Ham, de Rammelaars © Carina Van Steenwinkel: paraphyses in the uredinium

urediniospores
gall
uredinia mostly hypophyllous, 0.5 mm, yellow, with clavate paraphyses; urediniospores elliptic, very coarsely spinulose. Telia also hypophyllous, sub-epidermal, dark brown.
uredinia, telia
Salicaceae, narrowly monophagous
Populus alba, x canescens, tremula.
synonyms
Melampsora aecidioides, castellana, laricis-tremulae, magnusiana, pinitorqua, pulcherrima, and rostrupii form a complex of species, that collectively is addressed under the name M. populnea. They form strongly resembling uredinia and telia on Populus section Leuce (alba, x canescens, tremula), but aecia on widely divergent plant species. There is no consensus about the taxonomic status of the component species.
The interpretation of M. laricis Hartig, 1885 is not fully clear. According to Brandenburger and the Index Fungorum (2017)it is a junior synonym of populnea, but Klenke & Scholler point to M. caprearum.
Predators
Mycodiplosis coniophaga, tremulae
Hyperparasite of the uredinia
notes
Massive occurence of the uredinia stage, like in 2012, can bring forward a total early leaf fall.
references
Bahcecioglu & Kabaktepe (2012a), Brandenburger (1985a: 18, 38), Buhr (1965a), Chinery (2011a). Gjaerum (1987a), Gjaerum & Dennis (1976a), Gjaerum & Sunding (1986a), Henderson (2000a, 2004a), Jost (1987a), Jage, Scholler & Klenke (2010a), Kozłowska, Mułenko & Heluta (2015a), Mułenko, Sałata & Wołczańska (1995a), Negrean (1997a), Redfern & Shirley (2011a), Roskam (2009a), Ruszkiewicz-Michalska (2006a), Scholler & Schubert (1993a), Poelt & Zwetko (1997a), Spooner & Butterfill (1999a), Termorshuizen & Swertz (2011a), Tomasi (2014a), Tykhonenko (2010a), Vanderweyen & Fraiture (2007a), Vialle, Frey, Hambleton, Bernier & Hamelin (2011a), Woods, Stringer, Evans & Chater (2015a).