Sori on the underside of fronds of the common polypody fern, Polypodium vulgare. The life cycle of a fern consists of alternating generations of which

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Sori on the underside of fronds of the common polypody fern, Polypodium vulgare. The life cycle of a fern consists of alternating generations of which the green fern \plant\" is the asexual phase (the sporophyte generation). Mature fronds develop spore-bearing structures ( sporangia ), here seen as circular groups of yellow or brown particles. The groups are called sori ( singular, sorus ). The yellow sporangia are at an early stage of development. Eventually the spores within each sporangium are released, and on falling to moist ground, germinate to form a tiny green plant ( the gametophyte ), which goes on to produce male and female gametes. When these combine, a new fern plant ( sporophyte) is produced, and the cycle completed. P. vulgare is a widespread species found throughout N Europe, temperate Asia and western N. America. It grows on rocks, walls, and as an epiphyte on trees."

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Photo credit: © DR JEREMY BURGESS/SCIENCE PHOTO LIBRARY / Alamy / Afripics
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Keywords: biological, biology, botanical, botany, fern, frond, gametophyte, polypodium, polypody, sorus, sporangia, spore, sporophyte, vulgare