Microbotryum violaceum
Microbotryum violaceum, also known as the anther smut fungus, was formerly known as Ustilago violacea. It is a basidiomycete obligate parasite of many Caryophyllaceae. But it has now separated into many species due to its host specificity.
Meiosis in M. violaceum produces a tetrad of four haploid meiotic products. Pairwise intra-tetrad mating can occur between these meiotic products.