leptosporose

Leptosporose, from Greek lepto- “thin” and sporangion “sporangium,” refers to a mode of sporangium development found in most ferns (leptosporangiate ferns). In this condition, each sporangium originates from a single epidermal or hypodermal initial cell, forming a compact, thin-walled organ with a short stalk. By contrast, eusporangiate sporangia arise from several initial cells and are typically larger.

Leptosporangia are usually grouped on the undersides of fronds into sori, sometimes shielded by a protective indusium. The sporangium often contains an annulus, a ring of specialized cells that, as the sporangium dries, elastically moves to rupture the sporangial wall and ejects spores in a bouncy or catapult-like discharge. This mechanism promotes wide spore dispersal.

The life cycle follows the typical fern alternation of generations: a diploid sporophyte produces haploid spores by meiosis; spores germinate into a free-living, photosynthetic gametophyte (prothallus) that bears archegonia and antheridia; fertilization requires free water, producing a zygote that develops into a new diploid sporophyte.

Ecology and systematics: leptosporangiate ferns comprise the majority of living fern species, including many families such as Polypodiaceae, Dryopteridaceae, and Pteridaceae. They inhabit a wide range of habitats, from forests to rocky outcrops, often in moist environments. The leptosporangiate condition is a defining feature distinguishing most modern ferns from the eusporangiate lineages.