18005
Conyza sumatrensis ( Retz . ) E . WALKER ( Asteraceae ) is a spontaneous annual herb , fairly widespread throughout Tunisia , which has rarely been studied or valued in any sector .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 None