1. A sporangium formed from a single epidermal cell; characteristic of the Filicales or of almost all modern ferns

Type of: sporangium, spore case, spore sac

• optical crown
• optical crown glass
• optical density
• optical device
• optical disc
• optical disk
• optical fiber
• optical fibre
• optical flint
• optical fusion
• optical glass
• optical illusion
• optical instrument
• optical lens
• optical maser
• optical opacity
• optical phenomenon
• optical prism
• optical pyrometer
• optical rotation
• Inverness
• inverse
• inverse cosecant
• inverse cosine
• inverse cotangent