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The Western oak fern (Gymnocarpium dryopteris) belongs to the family Woodsiaceae. It is a summer-green fern that is distributed from the Chubu region of Honshu northward to Hokkaido in Japan, and widely in Eurasia and North America. It grows on the forest floor or rocks in mountainous areas and is 30-40 cm tall. The leaves are three times pinnate compound, about 20 cm long. The lowest pinna is large and almost the same size as the rest of the leaf, giving it the appearance of a trifoliate leaf. The petiole is much longer than the leaf blade, straw-colored to greenish-red, hairless, thin and brittle. The sorus is circular and attached to the lobes near the margins, without an indusium. The Japanese name comes from the leaf blade's shedding at the top of the petiole, which resembles the harelip.
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