Developmental morphology of Triangularia backusii (Sordariaceae)

Abstract

Perithecia of Triangularia backusii are initiated by a coiled ascogonium that consists of several uninucleate cells. No trichogynes are produced. Sterile hyphae which originate from stalk cells of the ascogonium envelop the ascogonium and develop into an outer zone that forms part of the peridium. Hyphae arising from the base of the ascogonial coil develop into two types of tissues: the middle zone forms part of the peridium and the inner zone forms the pseudoparenchymatous centrum tissue. When the young perithecium reaches a diameter of about 110 μm, the central mass of ascogonial hyphae spreads out as a result of perithecium growth and the pressure from the upward growing paraphyses, and the ascogenous hyphae start to develop from the ascogonial hyphae. At the same time periphyses begin to grow in the apical region. The uninucleate paraphyses and periphyses originate from large, thin-walled, multinucleate pseudoparenchyma cells. Asci appear when the young perithecium has assumed an ovoid shape and attained a diameter of about 140 μm. Each uninucleate ascogenous cell grows out into a uninucleate hook and the hook develops directly into an ascus.Elongation of asci and paraphyses and enlargement of core hyphae and pseudoparenchyma cells expand the perithecium, and disintegration creates a central cavity. Growth and enlargement of hyphae of the middle zone result in the formation of the perithecial neck. Periphyses continue to grow upward or horizontally until an ostiolar canal is formed. At maturity the pseudoparenchyma zone is thin at the sides but thick at the ostiolar region and bottom.Chadefaud's concept of the Sordariales is expanded to include four families: Chaetomiaceae, Lasiosphaeriaceae, Microascaceae, and Sordariaceae. These families include those fungi with the Sordaria type of centrum development proposed herein.