Asexual reproduction occurs via vegetative spores (conidia) or through mycelial fragmentation. Such individuals are usually exposed to organic dust heavily packed with conidia and mycelial debris. Mushroom-forming forest fungi are unique in that their mycelial mats can achieve such massive proportions. Sexual reproduction is by basidiospores arising from a teliospore developed from a mycelial clamp connection. The mycelial and yeast phases differ in their morphology, biochemistry, and ultrastructure. They are home to the world's largest organism and fungal mycelial mat, the Armillaria ostoyae. The lower leaf surface corresponding to the mycelial mat will also show chlorosis. Often, fungicides are used to inhibit mycelial growth. Cultures manifest a combination of mycelial and yeast-like growth forms, however the yeast-like typically predominates. Somatically, they form a morphologically similar mycelial wave front that continues to grow and explore. While the tree is alive, only sterile mycelial masses are produced (the black exterior conk). A pink or brown mat of mycelial threads may grow above the soil surface. A sunken canker then forms as the mycelial fan spreads under the bark. It is unusual to find both the mycelial and yeast forms co-existing. They are exuded from flasklike mycelial branches.