Waun Las in the National Botanic Garden of Wales was made the country's first national nature reserve last week.
The award, from deputy first minister Ieuan Wyn Jones, aims to safeguard the organic farm in Carmarthenshire for conservation and education.
"It plays a unique role in studying biodiversity, promoting conservation and educating people about the natural world," he said.
The natural oasis has 310 species of flowering plant, 331 lichens, mosses and liverworts, and teams with butterflies, moths and hoverflies.
Kevin Lamb, director of the botanic garden, said: "This is a fantastic opportunity to showcase Wales' floral biodiversity and that from around the world."