The University of Hawaii-Manoa campus is now accredited internationally as an arboretum, a designation that recognizes its more than 500 species of trees as an important collection.

The Morton Arboretum ArbNet selection puts the university in a prestigious group with only 134 other arboretums internationally, and which includes only one other in Hawaii.

The 320-acre UH-Manoa campus, established in 1907, features more than 4,000 trees, including a chaulmoogra planted by the king of Siam in 1935 to honor university researcher Alice A. Ball, who developed an injectable extract once used to treat Hansen’s disease.

The plants at the university’s Manoa campus range from Mediterranean to subtropical, capable of withstanding temperatures in the 30s.

“We have something in bloom pretty much year-round,” said horticulture professor emeritus Richard Criley.

When he taught horticulture, Criley would take his students on walks across campus to identify an array of ornamental trees. “The campus is our laboratory,” he said.

The campus also serves as an outdoor classroom for students of landscape architecture, art, geography, botany, Hawaiian studies, horticulture, entomology and natural resources, with its variety of palms and its colorful array of flowering trees.

While some trees like plumerias continuously bloom, others flower seasonally or under varying climate conditions.

Usually several weeks after heavy rain, golden shower trees or Cassia fistula, a native of India, burst into blooms of pale yellow flowers near Kuykendall, Gilmore and Wist halls.

After long days of summer, followed by shorter sunny days in the fall, a palmlike tree from Madagascar known as Ravenala madagascariensis blooms near Bachman Hall around October with bird-of-paradise-shaped flowers.

Some trees make one wonder what nature was thinking, like the tree from West Africa that bears a hefty fruit shaped like a sausage known as Kigelia africana, and the cannonball tree from the Caribbean coast of South America with cannonball-size fruit, known as Couroupita guianensis.

Then, there is the baobab tree that university horticulturalist say might be the largest in the country.

“I have a lot tourists calling and coming on campus,” said professor Andrew Kaufman, chairman of the Landscaping Advisory Committee, while pointing out various leafy attention-getters.

Several minutes later, as if on cue, a car slowed near Bachman Hall while visitors snapped photographs of a Baker’s shower tree or Cassia bakeriana, native to Thailand and Myanmar, that was in bloom in pink and coral shades.

MORTON Arboretum ArbNet has designated UH-Manoa as a level one arboretum. Nearby Lyon Arboretum in Manoa holds a level four — the highest obtainable accreditation.

Some 37 other universities and colleges enjoy the designation, including the University of Oxford in the United Kingdom.

Accredited institutions include Arlington National Cemetery, the Shanghai Botanical Gardens in China, and the Tasmania Arboretum in Australia.

University botanist Joseph Rock began planting trees on campus in 1915, increasing the list into the hundreds from around the world.

When Ball’s method of injecting Hansen’s disease patients became popular worldwide for treatment of symptoms, Rock received authorization from the U.S. Department of Agriculture to obtain seeds of the chaulmoogra tree to establish chaulmoogra plantations, according to a research paper on a National Institutes of Health website.

A plantation of 2,980 trees was established in Hawaii in 1921-1922. Growing chaulmoogra declined with the introduction of sulfone drugs that cured the disease, said medical historian John Parascandola in his research paper.

Criley said the university continues to support such research through its arboretum.

He said an East Coast researcher is looking at the medicinal benefits of the sun sapote tree, also known as Licania platypus, planted near Sinclair Library.

Organizers of the university’s arboretum designation hope to increase their inventory of trees to include more palms to a collection started by Rock, including species near extinction.

“This is a natural progression,” said Kaufman. “It’s really exciting.”