Filamentous fungi (molds) can be divided into 2 broad morphologically distinct groups: those that produce aseptate hyphae and those that produce aseptate (or rarely septated) hyphae. Identification of aseptate hyphae in tissue is virtually pathognomonic of zygomycosis (mucormycosis)-disease caused by fungi of the class Zygomycetes (order Mucorales). The discovery of septate hyphae in tissue is less diagnostic; septate hyphae may be caused by fungi that typically grow as yeasts (eg, Candida and Trichosporon) or a vast number of species of molds. The septate molds are often divided into those with darkly pigmented hyphae (phaeohyphomycetes) and those with pale or colorless (hyaline) hyphae (hyalohyphomycetes).
