Morphology of Meliola floridensis

Abstract

The black, superficial mycelium of Meliola floridensis on leaves of Persea borbonia produces long, stiff, simple spines, flask-shaped mucronate hyphopodia of undetermined function, and capitate hyphopodia from which globoid haustoria in the host epidermal and hypodermal cells originate. Ascocarps arise as flat radiate shields from cells that resemble the capitate hyphopodia. Cells cut off from the lower surface of the shield differentiate into one or two enlarged, uninucleate ascogonial cells and sterile hyphae that surround the ascogonia. The ascogonium becomes binucleate, possibly through an unobserved mitosis. Short, thick ascogenous hyphae form terminal crosiers. Proliferations from the fused apical and basal cells of the crosiers produce a close succession of asci. The asci, cut off by septa, stand on step-like indentations along one side of the non-septate ascogenous hypha. Sterile hyphae grow upward around the cluster of ascogenous hyphae and asci. The outer layers are compacted into a perithecial wall surrounded by, and fused with, the dark, thick-walled cells of the shield. The inner hyphae arch over the ascogenous hyphae and asci as lateral paraphyses. The uniformly thin-walled, unitunicate asci discharge their two brown, 4-septate ascospores forcibly. The Meliolaceae are unrelated to the Erysiphaceae and to the various groups of superficial Loculoascomycetes with which they have been classed in the old order Perisporiales (Erysiphales). They constitute a small, homogeneous family in the separate order Meliolales of the Pyrenomycetes.