Tar Spot

(Rhytisma acerinum)

               
Occurrence

Uncommon in Minnesota because the host is uncommon

 

No Image Available

Season

Spring to fall

Habitat/Hosts

Norway maple (Acer platanoides)

 

 

 

 


Identification

This is a parasitic fungus infecting several species of maple (Acer). In Minnesota it infects only Norway maple.

In the spring the infection appears as a yellow spot on the leaf. These turn first brownish-black with a yellow border, then, in late summer, black with a yellow border. The black spots resemble tar. The spots are solid, not a cluster of small spots. They may be up to 1½ in diameter but are usually much smaller.

The fungus is somewhat tollerant of air pollution and is often found in suburban locations.

 
Similar
Species

Speckled Tar Spot (Rhytisma punctatum) causes dense clusters of very small black spots.

Tar Spot (Rhytisma americanum) infects red maple and silver maple.


Distribution Distribution Map  

Sources: 4, 26, 29, 30.

Until 1998 this species name included what is now recognized as Rhytisma americanum. Some or all of the records represented on the map at left may be Rhytisma americanum.


Comments

Two Scientific Names
The life cycle of this and most other fungi is pleomorphic. It has both an asexual reproductive phase (anamorph) and a sexual reproductive phase (telemorph). Each phase is often morphologically distinct. In the past, the International Code of Botanical Nomenclature allowed each phase to be assigned a different scientific name. It was incorrect to refer to the anamorph phase by the telemorph name, and vice versa. Some mycologists and molecular biologists consider this practice to be obsolete. Molecular phylogeny allows the accurate placement of a species in any part of their life cycle. On July 30, 2011, at the meeting of the XVIIIth International Botanical Congress in Melbourne, Australia, that practice ended. Prior to that meeting, the early, anamorphic phase of this fungi had been named Melasmia acerina. Both phases are now named Rhytisma acerinum.


Taxonomy

Division:

Ascomycota (ascomycetes)

  no rank:

saccharomyceta

 

Subdivision:

Pezizomycotina

 

No Rank:

leotiomyceta

 

No Rank:

sordariomyceta

 

Order:

Rhytismatales

 

Family:

Rhytismataceae

 
Synonyms

Melasmia acerina

Xyloma acerinum

 
Common
Names

Sycamore Tarspot

Tar Spot


 

 

 

 

 

 

       

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  Rhytisma acerinum - fungi kingdom
Nineli Lishina
 
   
 
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Published on Jan 25, 2015

Rhytisma acerinum - fungi kingdom

 
     

 

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  Insights into Nature - Tar Spot Fungus on Sycamore
Roger Griffith
 
   
 
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Published on Oct 27, 2014

The Tar Spot (Rhytisma acerinum) is a very common ascomycete fungus that typically grows on Celtic Maple / Sycamore (Acer pseudoplatanus) leaves giving a prominent black spot or spots on the leaf lamina, upper and lower epidermal surfaces. It is reported to grow occasionally on Norway Maple (Acer platanus) leaves.

 
     

 

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