Saturday, March 31, 2012

Ostrich fern and Sensitive fern dropping spores

What:  Sporangia on fertile fronds of both sensitive fern (Onoclea sensibilis) and ostrich fern (Matteuccia struthiopteris) open and drop their spores early in the spring.

Ecological notes: Of our local ferns, only a small handful have the spores located on separate fronds (called fertile fronds). Examples include sensitive fern, ostrich fern, royal fern, and sort of intermediate fern. All of these are adapted to wet areas. Could be that having separate fronds allows them to protect the spores throughout the winter in the modified pinnae (that form the little balls) and then as the snow melts, drop their spores to be dispersed in the spring runoff to other spots where water pools.

Where: I find ostrich fern in sandy, but moist and enriched soils with moderate to high pH. Sensitive fern tends to like it wetter than ostrich fern (and therefore in more clay-ey, silty soils than ostrich fern). This patch is on a slope with a high water table.

Other notes: To tell the two species apart, ostrich fern has much larger more robust, wider spreading fertile fronds than the more delicate sensitive fern fronds. Ostrich fern also has fronds that are born out of a small dense cluster. In winter, you will readily notice the small dark knobs sticking out of the ground in a patch of ostrich fern. Sensitive has single blades that come out of the ground (these are often clumped loosely), but don't come out of the ground from a single point so you won't see the same lumpiness to the ground.

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