As a botanist Hacquet wrote a book on alpine flora from Carniola called Plantae alpinae Carniolicae. The botanical genus Hacquetia is named after him, as well as the plant species Pedicularis hacquetii (Hacquet's lousewort). On one of his excursions, he discovered on the evening, Trenta side of Triglav, a new species of scabious and picked it for his herbarium collection, nowadays preserved in the Natural History Museum of Slovenia. He called the species Scabiosa trenta in the published description, and drew it. Many botanists have sought the mysterious pale yellow scabious, among them also the young Julius Kugy. He searched for the mysterious flower, and though he was not able to find it, this led him to become a great explorer and describer of the Julian Alps. The Austrian botanist, Anton Kerner von Marilaun, later proved Belsazar Hacquet had not found a new species, but a specimen of the already known submediterranean Cephalaria leucantha.