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Over 50 species are found petrified at the site , including ginkgo , sweetgum , redwood , Douglas fir , walnut , spruce , elm , maple , horse chestnut , cottonwood , magnolia , madrone , sassafras , yew , and witch hazel .
 ginkgo, sweetgum, Douglas fir, walnut, spruce, elm, maple, horse chestnut, magnolia, madrone, sassafras, yew
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 ginkgo, sweetgum, Douglas fir, walnut, spruce, elm, maple, horse chestnut, magnolia, madrone, sassafras, yew