Conjugation, with delayed fusion of nuclei, produces dikaryotic hyphal strands. The tips of these strands form cross walls to isolate a tiny sac or ascus . Ascomycetes are often referred to as sac fungi . The two nuclei in the ascus fuse together into a diploid nucleus, which then undergo meiosis to form four haploid ascospores , which then divide again by mitosis to form eight haploid ascospores . Asexual reproduction is accomplished by conidia bearing conidiospores.
Basidiomycetes produce fruiting bodies called basidiocarps .
Club-shaped structures called basidia hang from the underside of the mushroom, lining thin flaps of tissue called gills . Within these basidia, nuclear fusion occurs, followed by meiosis to produce four basidiospores . Because of the shape of the basidium, basidiomycetes are sometimes called club fungi . By focusing on sexual reproduction in classifying fungi, we fell into a taxonomic trap. Many species of fungi have never been observed to undergo sexual reproduction.