Development of merosporangia in Linderina pennispora (Kickxellales, Kickxellaceae)

The vegetative and sporulating structures of Linderina pennispora are described using scanning and transmission electron microscopy. The vegetative hyphae and sporangiophores were regularly septate, possessed a two-layered wall, and coated with rod-shaped, 0.2–0.7 μm long, 0.15–0.25 μm wide ornamentations. The sporangiophore was erect, cylindrical, and narrower (4–8 μm) than the vegetative mycelium (8–12 μm). The mature sporocladium was ovoid to dome-shaped, sessile, non-septate, 18–24 μm diam, possessed a two-layered wall, and coated with rod-shaped ornamentations. Mature pseudophialides were ellipsoid, 2.0–2.5 μm wide, 4–7 μm long, possessed a two-layered wall, and formed in a series of concentric groups radiating from the “apex” of the sporocladium. The pseudophialides had a round, ca. 1.5 μm diam, base with a narrower, 0.7–0.8 μm diam lobed, cylindrical neck structure in the distal region which extended to the pseudophialide neck. The merosporangia were obovate, 3–4 μm wide near the base, and narrowed distally to 2.0–2.5 μm wide, 18–23 μm long, possessed a three-layered wall, with regular surface annulation with interconnecting ridges, but lacked rod-shaped ornamentations. The merosporangia contained a single, obovate, 2.3–2.5 μm diam merosporangiospore, with a ca. 1 μm diam papilla-like base, that possessed a four-layered wall. Detached merosporangia had a single, acicular, unbranched, 3–5 μm long, ca. 0.1 μm diam “appendage” that was attached to the merosporangiospore inner cell wall layer and passed through the septum plug to the pseudophialide.