The U.S. Department of Agriculture has begun to identify the mysterious seeds that have been mailed to the United States from China.
On Wednesday, a USDA official said in a statement that 14 different species of the seeds have been identified so far. They include seeds of flowering plants, herbs and vegetables.
Anyone with unsolicited seeds is urged not to plant them and to alert local officials.
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"We have identified 14 different species of seeds, including mustard, cabbage, morning glory and some of the herbs, like mint, sage, rosemary, lavender, then other seeds like hibiscus and roses," said Osama El-Lissy of the USDA's Animal and Plant Health Inspection Service.
"This is just a subset of the samples we have collected so far," he said.
Earlier this week, officials in at least 28 states urged residents to report any unsolicited packages of seeds that appear to have been sent from China because they could be harmful.
"Based on information provided by constituents, the packages were sent by mail and may have Chinese writing on them," the Delaware Department of Agriculture said in a statement Monday. "All contained some sort of seed packet either alone, with jewelry, or another inexpensive item."
The USDA explained in a statement on its website that it did not have any evidence that the seeds are something other than a "brushing scam," where people receive unsolicited items from a seller who then posts false customer reviews to boost sales.
"USDA is currently collecting seed packages from recipients and will test their contents and determine if they contain anything that could be of concern to U.S. agriculture or the environment," the statement said.