The trip to Sweden is primarily aimed at their participation in events commemorating the 300th anniversary of the birth of Swedish biologist Carolus Linnaeus, who invented the current system of classifying organisms.
The emperor is known for his interest in the goby fish and is an honorary member of the Linnean Society of London, an academic institute named after the Swede.
On Tuesday, Akihito, 73, and Michiko, 72, toured the Bergius Botanic Garden, which is celebrating the Linnaeus tricentenary with a special exhibit.
The couple arrived at the gardens on board the Sjöfröken steamboat from 1875, accompanied by Sweden’s King Carl XVI Gustaf and Queen Silvia, after a five-minute crossing from Haga Palace in the lush English-style Haga Park where the imperial couple is staying.
Under cool, grey skies, the royals toured the gardens for a half-hour, stopping often to comment on various species of Swedish and foreign flowers and plants, including tulips, peonies, bleeding heart and oak and pine trees.
The empress, dressed in a white suit with navy trim and white hat, was seen chatting easily with Queen Silvia, clad in a lilac coat, in English without an interpreter, while the emperor and king followed suit.
Security was tight during the visit, with helicopters buzzing overhead as police could be seen searching the gardens’ dense greenery and bushes. A police boat blocked off the waterway below.
Birgitta Bremer, the director of the gardens who guided the royal tour, said the Japanese emperor and empress were keen to see all the species.
“They were very interested in all the plants. They recognized a lot of species,” she told AFP afterwards, admitting that she was “a little nervous” because “it’s not every day that you meet the imperial couple”.
Following the visit to the gardens, Akihito and Michiko attended a luncheon with the Swedish government hosted by Prime Minister Fredrik Reinfeldt and his wife Filippa at the foreign ministry.
Later Tuesday, the imperials visited the Royal Swedish Academy of Sciences, which Linnaeus helped found in 1739 and which each year awards the prestigious Nobel Prizes in the fields of chemistry, physics and economics.
Rounding off the day was a visit to the Museum of Natural History, to see an exhibit entitled “From Linnaeus to DNA”.
The imperial couple also examined the museum’s original 1784 copy of “Flora Japonica”, a book written by Linnaeus protege Carl Peter Thunberg which for the first time categorised more than 800 species of Japanese plants, museum officials said.
The emperor was also shown the museum’s fish database, the largest in the world, and received a copper engraving from 1790 depicting two Japanese fish drawn by Thunberg.
On Wednesday, Linnaeus’ 300th birthday, festivities commemorating the renowned botanist will primarily take place in Uppsala, a small town north of Stockholm where he worked as a university professor in the 18th century.
The imperial couple will attend a memorial ceremony early Wednesday in Uppsala Cathedral, followed by a celebration at the Uppsala University auditorium and a banquet at Uppsala Castle.
Their trip to Sweden follows a state visit in 2000, and comes on the heels of a visit by the Swedish king and queen to Tokyo in March.
On Thursday the imperial couple will leave Sweden for the three Baltic states before heading to Britain.