Lactarius chromospermus (igisazi)

Lactarius chromospermus is a species of ectomycorrhizal fungus, meaning that it must associate with the roots of its host plant in order to develop and survive. Ectomycorrhizal fungi forge symbiotic relationships by forming a sheath around the root tips of its host. The fungus takes organic compounds from the plant, and in return provides the plant with water and nutrients from the soil. Other benefits to the plant may include improved defence against herbivores and resistance to toxins and pathogens.

Ectomycorrhizal relationships are common in most temperate and some tropical forests. One taxonomic group of tropical legumes, the Berlinia clade (such as Isoberlinia doka, Gilbertiodendron dewevrei and Berlinia razzifera) is thought to form ectomycorrhizal relationships with fungi – other legume groups mainly form a different type of mycorrhizal association, arbuscular mycorrhiza, with Glomeromycota fungi.

Lactarius chromospermus is only found in tropical Africa and is probably restricted to the Zambezian region. It occurs in Burundi, Tanzania, Zambia and Zimbabwe.

Lactarius chromospermus (Image: © Bart Buyck)

The cap (pileus) is firm and measures 4–14 cm diameter. The outer skin (pellis) is smooth and dry, but greasy when humid. It ranges from cream or pale yellow to greyish yellow and greyish orange in colour. The latex can be scarce to abundant and is white but dries with a yellowish tinge. The spore-deposit is dark brown, fading to chestnut brown, an exceptional colour in this family.

Underground, the ectomycorrhizal sheath has distinct hyphae (filaments that form the vegetative part of fungus) with latex and cystidia (large, sterile cells with unknown function).

According to the literature, Lactarius chromospermus only forms ectomycorrhizal relationships with species in the legume genus Brachystegia (including B. utilis and B. spiciformis). However, similar symbiotic associations with other tree genera cannot be excluded as such relationships are common in tropical Africa. High host specificity is uncommon, and many tropical ectomycorrhizal fungi are able to colonise several different plant species.

The name igisazi given by the people of Rumonge (Burundi) is a general term for inedible mushrooms. Only a few species in the Russulaceae family are eaten in Burundi, perhaps because the dark brown lamellae give the species the appearance of an Agaricus, a genus usually regarded by Africans as toxic.

Preserved specimens of Lactarius chromospermus, including the type, are maintained in the Kew Mycology Herbarium and, although not accessible to the general public, are available for study by researchers worldwide.

 MycoBank - Lactarius chromospermus

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