#3734 - Cephaleuros lagerheimii - Māhoe Leafspot
To my great surprise, this plant disease is actually a orange terrestrial alga (which are actually green algae) pretending to be a rust fungus. My flabbers were well-and-truly gasted.
The generic epithet is Latin for 'mold-head', and refers to the reproductive structures that resemble those of mold fungi. The specific epithet honours Swedish botanist, mycologist, phycologist, pteridologist and pioneering pollen scientist Nils Gustaf Lagerheim (1860–1926).
Despite the common name, it doesn't just infect Māhoe (Melicytus ramiflorus) - it can target a range of species in the coffee and madder family Rubiaceae, and is known from China and South America as well.
The genus is widespread, and usually parasitise flowering plants, although a few are known from gymnosperms. The spores germinate after rain, but it's not clear how they penetrate the leaf tissues. There are also species that form a symbiosis with fungi to become a harmless lichen, and others where the fungus is using the alga to parasitise the plant.
A single fossil is known, from the Middle Eocene of Tennessee.
The family Trentepohliaceae contains five genera - another parasitic genus, and three that grow on rock, soil, and treetrunks or as epiphytes on the leaves on larger plants, or as the photobiont in many species of lichen.
Woodhaugh Gardens, Dunedin, Aotearoa New Zealand
