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Family Asteraceae:  Determination of the Pure Seed Unit
by Sue Alvarez, R.S.T., Ransom Seed Laboratory
Presented at the 2005 Native Seeds Symposium, Saskatoon, Canada

There is a generally recognized problem in the purity testing of certain native species in the Asteraceae family. 

The focus of this paper is to identify the problem starting with the history of the “Pure Seed Unit” (PSU) definitions for Asteraceae in the Rules for Testing Seeds of the Association of Official Seed Analysts (AOSA).  The current AOSA Rules are compared to those of the International Seed Testing Association (ISTA) as well as the Canadian Methods and Procedures for Testing Seed.  Examples and special problems in testing native Asteraceae species are presented.  Finally, ideas for new Asteraceae PSU are introduced.



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