3 public questions tagged with this topic.
Phycomycetes possess aseptate and coenocytic mycelium. Their motile asexual spores are zoospores, whereas their non-motile asexual spores are aplanospores. Both are produced endogenously inside a sporangium.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Fungi - Phycomycetes Ascomycetes Basidiomycetes
Annulus consists of specialized row of thick-walled hygroscopic cells with inner and radial walls heavily thickened with lignin in U-shaped pattern, forming arc partially encircling leptosporangium capsule on one side. Upon dehydration under low humidity, annulus cells lose water, contract differentially, storing elastic energy, then snap backward violently rupturing stomium region and ejecting spores catapult-like up to several centimeters into air stream. Nutrition or protection functions performed by tapetum and indusium, germination unrelated process. Presence and position provide taxonomic characters distinguishing fern families.
Ref: Goebel Organography; Hollowell Fern sporangium mechanics, Ann NY Acad Sci; Campbell
Most extant ferns belonging to Polypodidae and core leptosporangiate clade are leptosporangiate, originating from single superficial initial cell undergoing precise periclinal and anticlinal divisions producing small stalked sporangium with distinct annulus, stomium and limited spore number typically 64 or 128. Primitive ferns like Ophioglossales and Marattiales are eusporangiate with larger thicker-walled sporangia from multiple initials. Leptosporangiate development enables massive spore production per frond, synchronized maturation, and explosive catapult dispersal, representing derived trait linked to diversification of modern fern families in Mesozoic.
Ref: Bower 1891 Eusporangiate vs Leptosporangiate; Gifford & Foster; PPG I 2016 Ferns
