|Oooh, baby, get a load of those sori!|
Photo by kqedquest
Good ol' sword ferns are abundant in virtually any moist forest west of the Cascades. Compared to plants that flaunt gaudy flowers as a reproductive come-on, sword ferns lead quiet, strait-laced sex lives. They reproduce with decorum, forgoing both flowers and seeds.
Ferns make more ferns in a two-step process. A mature plant produces small rusty circles, called sori, on the underside of its fronds. These circles, which neatly line up along the margins of each leaflet, contain microscopic spores, and each plant produces millions.
The spores eventually fall to the ground or are carried by the wind. If moisture and light conditions are right, the spores will grow into tiny heart-shaped plants called prothallia. These reproduce sexually to become young fern plants.
Sperm and egg cells grow on the undersides of the prothallia leaves and require a drop of moisture to unite. Then the sperm cells, drawn by a chemical attractant, swim through the water to fertilize the eggs. A fertilized egg divides and redivides and finally creates new leaves unlike those of the heart-shaped prothallia. Additional leaves become more fern-like, eventually taking on the characteristic broad-sword shape the plant was named for.
Thoughout the spring and summer I like to note the progression in the cycle by occasionally tipping up the underside of a frond to see how the sori are developing.
Go ahead and take a peek--they won't mind.