Lactarius chromospermus (igisazi)
Lactarius chromospermus (Photo: Annemieke Verbeken)
Lactarius chromospermus Pegler
Not evaluated according to IUCN Red List criteria but considered rare.
Miombo woodland (woodland, characteristic of the Zambezian region of Africa).
About this species
Lactarius is a fungal genus in the group commonly known as milk-caps, as they often exude latex (milky fluid) when cut. The large milk-cap group has recently been split in two genera: Lactarius and Lactifluus. Lactarius is well represented in tropical Africa and Madagascar with 40 currently accepted species, although it is probable that over 70 species exist.
The genus Lactarius was described in 1797 by the South African scientist Christian Hendrik Persoon – the ‘Prince of Mycologists’. The species L. chromospermus was described in 1982 by David Pegler, previously the Head of Mycology at Kew. Its most striking characteristics are its chocolate brown gills and spore print, which is outside the known white to yellow colour variation of the other agaricoid Russulales genera.
Geography and distribution
Lactarius chromospermus is only found in tropical Africa and is probably restricted to the Zambezian region. It occurs in Burundi, Tanzania, Zambia and Zimbabwe.
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).
The symbiotic relationship with its host plant
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.
Associations with Brachystegia
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.
'Igisazi' - inedible mushrooms
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.
This species at Kew
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.
Buyck, B. & Verbeken, A. (1995). Studies in tropical African Lactarius species. 2. Lactarius chromospermus Pegler. Mycotaxon 56: 427-442.
Pegler, D. N. (1982). Agaricoid and boletoid fungi (Basidiomycota) from Malawi and Zambia. Kew Bulletin 37: 255-271.
Petersen, R. H. (1977). Some brief reflections on C.H. Persoon. Kew Bulletin 31: 695-698.
Verbeken, A. (1995). Studies in tropical African Lactarius species. 1. Lactarius gymnocarpus Singer ex R. Heim and allied species. Mycotaxon 55: 515-542.
Verbeken, A. & Walleyn, R. (2010). Fungus Flora of Tropical Africa Volume 2: Monograph of Lactarius in Tropical Africa. National Botanic Garden of Belgium, Meise.
Kew Science Editor: Malin Rivers
Kew contributors: Martin Bidartondo
Copyediting: Nicola Merrett
Kew would like to thank the following contributors: Annemieke Verbeken