Eriophorum

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Cotton grass by Andrew Kearton
Via Flickr:

Eriophorum angustifolium, commonly known as common cottongrass or common cottonsedge, is a species of flowering plant in the sedge family Cyperaceae. Native to North America, North Asia, and Northern Europe, it grows on peat or acidic soils, in open wetland, heath or moorland. It begins to flower in April or May and, after fertilisation in early summer, the small, unremarkable brown and green flowers develop distinctive white bristle-like seed-heads that resemble tufts of cotton; combined with its ecological suitability to bog, these characteristics give rise to the plant’s alternative name, bog cotton.