Masahiko Hayashi, 56, was fined R75 000 by a regional court in Oudtshoorn, about 400km east of Cape Town, Johannesburg-based The Star newspaper reported.
"He was definitely on a collection trip and it was well planned. He had detailed topographical maps and had highlighted the farms where some of these succulents grow," said Pail Gildenhuys from the "green crime unit" of Cape Nature Conservation.
Gildenhuys said he had searched the professor's hotel room in Oudtshoorn last week and found 564 protected plants.
SAPA news agency reported that the plants were from the Haworthia genus, much sought-after in Japan where it has become a collector's item.
It said Hayashi was a recognised authority on Haworthias, and contributed to "Haworthiad" magazine, the quarterly journal of the international Haworthia society.
Haworthias are relatively small, often spiky-leafed plants, and come in a number of shapes and markings. They grow in the wild almost exclusively in South Africa.
Hayashi entered into a plea bargain with the state, and was fined and had his Global Positioning System equipment and the succulents confiscated.