The U.S. Department of Agriculture (USDA) has identified some of the plant species in bags of unsolicited seeds arriving in mailboxes across the United States from China.
Officials have warned that the shipments of mystery seeds, which appear to have originated in China, could be invasive plant species.
But so far, the species appear to be innocuous.
At least 14 of the seed species had been identified as of July 29, according to Deputy Administrator Osama El-Lissy of the USDA's Animal and Plant Health Inspection Service.
They include staples such as mustard and cabbage as well as herbs like mint, sage, rosemary and lavender.
The seeds of flowers were also included.
Although the species identified so far are harmless, plant experts have warned that seeds from other parts of the world could damage crops.
The Agriculture Department has said the packages are most likely part of a "brushing" scam, in which a seller sends unsolicited items to someone and then posts false positive customer reviews to boost sales.
"Brushing scams involving seed packets in international mail shipments are not uncommon," the USDA said.
"U.S. Customs and Border Protection (CBP) has intercepted similar seed shipments in recent years."
The seeds typically arrive in white packages displaying Chinese lettering and the words "China Post."
To date, all 50 states have reported receiving the suspicious packages of seeds.
The USDA has advised persons who receive the packets of seeds - not to plant them and “contact your state plant regulatory official”.