Photos of the Week



Leafy mistletoe can often have just green stems or reduced leaves growing in arid regions. This is Phorodendron densum with small leaves growing on Arizona Cypress. 


cut burl

Galls on trees are made up of disorganized cells and can be very dense. They can be made into very interesting and beautiful objects for display.


Fruiting bodies as they appear at the base of a red pine.

 Heterobasidion irregulare fruiting bodies at base of tree. This pathogen has recently been found in southeastern Minnesota and is expected to spread as it has done in Wisconsin. WI DNR reports 28 counties in Wisconsin with Heterobasidion Root Disease. Be on the lookout for this pathogen in Minnesota.


Here are some petri dishes with Armillaria glowing. In the back ground is a bag of wood sawdust inoculated with Armillaria which is also glowing.

Petri dishes and bags of bioluminescent fungi glowing in the lab. Armillaria, a root rot pathogen, has mycelium that glows in the dark.

pine board with white pocket rot

A pine board with white pocket rot. These interesting white rot fungi have the ability to selectively degrade lignin leaving cellulose behind. Some fungi, such as Porodaedalea (Phellinus) pini, produce small spindle-shaped white pockets while some other white pocket rot fungi produce much larger zones of delignification.

Blue stain in pine bowl

 Blue stain fungi impart dark discoloration to wood from their pigmented hyphae. Blue stain can lower the quality of wood used for wood products but in some cases, such as this turned pine bowl, it can add value.

zone lines

 Zone lines or pseudosclerotial plates are made up of fungal melanin that acts to separate incompatible white rot fungi from each other. Often called spalted wood, it is used by woodworkers and artists to make interesting objects.

basidia and basidiospores

As you eat the Pleurotus, remember meiosis has occurred in the basidia and those gills are filled with hundreds of thousands of extraordinary basidiospores.


Pleurotus fruiting

Pleurotus ostreatus fruiting to the size of dinner plates! And these will end up on student's dinner plates


Pleurorus fruiting

Second successful production of Pleurotus this semester - isolated, grown in pure culture, inoculated into spawn, inoculated into bags and fruited.


hawthorn rust

 Aecia on the bottom surface of a hawthorn leaf caused by Cedar-Hawthorn Rust, Gymnosporangium globosum.

Telia on Juniper Broom rust

 Juniper broom rust with telia coming out of the branches. The telia produce basidiospores that infect serviceberry (Amelanchier) 

fusiform rust

Fusiform rust with pycnia oozing pycniospores. This sweet liquid attracts insects that move the pycniospores from one pycnium (+) to another of an opposite mating type (-).

blister rust

Aecia of white pine blister rust on an infected white pine. The aecial stage is only seen in a 1-2 week period around the beginning of June. This blister-like aecia give the disease its name "blister rust".


When mature and released from the hysterothecia, the long thin ascospores have a sticky sheath that helps them adhere to needles.

 Lophodermium has long, thread-like ascospores with a sticky sheath that helps adhere them to needles after they are ejected out of the hysterothecium. 


Hysterothecia (also refered to as apothecia covered by stroma) on pine needles infected by Lophodermium.

 Lophodermium on old pines needles showing black hysterothecia. These black fruiting bodies open producing ascospores from the compressed apothecium that is under the black stromatic material.


Asexual stage of Ophiostoma

The Synnemata of Ophiostoma novo-ulmi with spores masses of asexual spores can be beautiful but this fungus packs a powerful punch and is responsible for killing hundreds of millions of elm trees in the United States.


The fungus causing oak wilt produces fungal mats under the bark.

 A red oak infected with oak wilt the previous year will produce oak wilt mats under the bark the following year. In spring, the pressure pads break open the bark and the aromatic fungus attracts Nitidulid beetles. The photo shows the pressure pads of the fungal mat when the bark was pulled off. These mats would be full with conidia and if both mating types are present, perithecia will also form.


newman canker

 What fungus do you think caused this type of canker on this ash tree?


Anthracnose on oak after early spring infection. Symptoms can look like a wilt disease.

Spring infection of oak with oak anthracnose when leaves are just forming can mimic the symptoms of oak wilt. However, there are ways to differentiate oak wilt from oak anthracnose. Can you determine this?


maple anthracnose

 This homeowner asks "Will my maple tree die?" Maple anthracnose can cause problems when we have a wet spring. Do trees die from anthracnose?



Pleurotus Basidiomycota

The mushroom-like fruiting body of a pink Pleurotus. This fungus would be classified in the Basidiomycota and produces basidia and basidiospores on its gills. 

witches cauldron Ascomycota

An example of a fungus in the Ascomycota. This cup-like fruiting body produces asci and ascospores. It is called the witches cauldron and is a rare and endangered fungus found growing in spruce bogs.

Salt damage on maple leaves.

 These maple leaves have a problem. Can you determine if this is caused by an abiotic or biotic agent?


red pines

Keeping forest and urban landscape trees healthy requires a good knowledge of tree diseases. This class will provide you with important information you can use in the future. Watch this page for new photos each week.