Cedar-hawthorn Rust

(Gymnosporangium globosum)

Conservation Status
Cedar-hawthorn Rust
 
  IUCN Red List

not listed

 
  NatureServe

not listed

 
  Minnesota

not listed

 
           
           
           
 
Description
 
 

On eastern redcedar, abnormal growths (galls) are formed on the stems, twigs, and branches. They first appear in the spring. They are reddish-brown, globe-shaped, and to 9 16 in diameter. They grow slowly throughout the summer and are mature by the fall. During wet periods they produce gelatinous, orange spore horns on their surfaces.

On hawthorns, bright orangish-yellow spots appear on the leaves. They first appear in early June, and are visible on both the upper and lower leaf surfaces. In midsummer fruiting bodies (aecia) are produced on the underside of the leaf. The aecia are tube-shaped, up to ½ long, and rusty brown.

 
     
 

Similar Species

 
     
     
 
Habitat and Hosts
 
 

Evergreen hosts: Chiefly eastern redcedar; sometimes also creeping juniper and common juniper.

Deciduous hosts: Most hawthorns; sometimes also serviceberry, mountain ash, apple, and crabapple.

 
     
 
Biology
 
 

Season

 
     
 

 

 
 

Life Cycle

 
 

It requires two hosts and two years to complete the life cycle of this fungus. In the early spring of the first year, galls on junipers produce gelatinous cones called telial horns. These horns release spores, mostly at night and early morning, that drift with the wind. Some of these spores land on dew-moistened leaves, fresh twigs, or fruit of a deciduous host. If the landing site remains wet for 4 to 6 hours, the spores germinate and penetrate the host. After a few weeks the first visible symptoms occur on the host. About 80 to 90 days after infection, fruiting bodies, called aecia, are produced. Aecia are produced chiefly on leaves, sometimes on twigs and leaf stalks, rarely on fruit. In mid-summer to early fall the aecia split and release spores which drift in the wind. Some of these spores land on and infect an evergreen host. The fungus overwinters on the new host with no visible symptoms. In the early spring of the second year galls are formed on the evergreen host. The galls grow throughout the summer and are full size by the fall. The galls overwinter and in the early spring of the third year produce telial horns, completing the life cycle. These galls often produce spores for more than a year.

 
     
 
Distribution
 
 

Distribution Map

 

Sources

4, 7, 26, 29, 30.

 
  9/16/2021      
         
 

Occurrence

 
 

 

 
         
 
Taxonomy
 
  Kingdom Fungi (fungi)  
  Subkingdom Dikarya  
  Division Basidiomycota (club fungi)  
  Subdivision Pucciniomycotina  
  Class Pucciniomycetes  
 

Order

Pucciniales (rust fungi)  
 

Suborder

Uredinineae  
 

Family

Gymnosporangiaceae  
 

Genus

Gymnosporangium  
       
 

Until very recently, the genus Gymnosporangium was placed in the family Pucciniaceae. Studies showed that the genus did not belong to Pucciniaceae orto any other existing rust family. In an article published 12/31/2020, it was proposed that a new family Gymnosporangiaceae be created to accommodate the genus. At that time the order Pucciniales (rust fungi) did not have any suborders. In an article published on 7/2/2021 a framework of seven suborders was proposed containing 80% of all rust species.

 
       
 

Synonyms

 
 

Gymnosporangium fuscum var. globosum

 
       
 

Common Names

 
 

American Hawthorn Rust

Cedar-hawthorn Rust

Hawthorn Rust

 

 

 

 

 

 

 

Glossary

Gall

An abnormal growth on a plant produced in response to an insect larva, mite, bacteria, or fungus.

 

 
 
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