The University of Hawaii’s Lyon Arboretum is easy to miss, up a winding, pitted roadway with a humble sign, largely overlooked by the crush of hikers heading to Manoa Falls.

But this botanical gem and scientific storehouse is going strong, playing a vital role in preserving Hawaii’s unique heritage. It will kick off its centennial celebration with a hoolaulea Saturday.

“People just think it’s a small botanical garden where people can come and walk around and it’s pretty,” said Lyon’s director, Rakan “Zak” Zahawi. “Some confuse it with Manoa Falls. Very few people outside of the field know the research end of things being done here and the more formal outreach of the educational department.”

Founded in 1918 by the Hawaiian Sugar Planters Association as a test site for growing trees for reforestation, the arboretum outgrew that purpose long ago. Today Lyon’s mission is multifaceted: It is a field research unit of the university, a botanical garden, a genetic bank of biodiversity for the state, an educational magnet for school­children and a powerful force for preservation.

Zahawi, a tropical biologist and restoration ecologist who took the helm in October, came from Costa Rica where he directed the Las Cruces Biological Station. He arrived in Manoa in time to shine the spotlight on Lyon’s many activities during its milestone year.

Although Hawaii has less than 1 percent of the land mass in the United States, it is home to more than 40 percent of the nation’s threatened and endangered plant species. Lyon Arboretum is helping keep many of them alive, deep in Manoa Valley.

“One of the really astounding units here to me is the Hawaiian Rare Plant Program,” which conserves and propagates threatened plants, Zahawi said.

“Basically, it’s a germ plasm warehouse where you are storing live material indefinitely for species that are on the brink of extinction in some cases or have actually gone extinct in the wild,” he said. “You’re creating a safe house for that material while you hopefully create better conditions in the field to put them back.”

Lyon’s Seed Conservation Laboratory holds 26 million seeds, belonging to about 600 species. Efforts to collect and store ohia seeds in response to the rapid ohia death crisis recently boosted that number by 4 million.

The arboretum’s micropropagation laboratory grows live tissue of native plants that do not store well as seed. It recently moved from a century-old cottage into a state-of-the-art building with a matching architectural look, and houses 30,000 specimens.

“I call them test-tube babies,” Zahawi said. “Literally, they are cuttings of a plant in a standard test tube with a growth media at the bottom.”

The arboretum staff works with state agencies, nonprofits and university researchers to conserve and restore native species across the islands.

In addition to those efforts, the 194-acre arboretum and botanical garden itself attracts visitors from around the world. It contains plants from just as far afield, acquired over many decades, with an estimated 5,000 tropical species on its grounds, including a large variety of palms.

Researchers, nature lovers and hikers roam its trails, some venturing as far as Aihualama Falls. Meanwhile, Lyon Arboretum’s education program introduces schoolchildren to the wonders of nature each year.

“Once the schedules open up for an academic school year, it just fills up like that,” Zahawi said, snapping his fingers. “Schools from all over the island bring students up here, and we have a number of different teaching units to do field-based learning.”

Raedelle Van Fossen, a former science teacher at Kawananakoa Middle School and a strong believer in the importance of getting kids outdoors, brought her environmental club to the arboretum — and eventually returned for good in hopes of reaching even more students.

“I just fell in love with it,” said Van Fossen, Lyon’s education manager. “For me this place is magical. … Working here with all the greenery, the wealth of knowledge of all the staff, with the people in the labs, in the greenhouse and on the grounds, it’s a really awesome place to learn something every day.”

She is seeking more volunteers who like to work with children outdoors to keep up with demand for its School Tours Program. The arboretum also offers classes for adults with topics ranging from beekeeping to crafting.

Despite its wide reach, the arboretum has only a small staff of 22 regular employees and an operating budget of about $2 million. It relies on an array of volunteers.

The arboretum was named after plant pathologist Harold L. Lyon, who led the original reforestation project for the Sugar Planters Association. Once that was complete, he spearheaded the donation of the site to the university in 1953 as an arboretum and botanical garden.

Saturday’s hoolaulea, which is free and open to the public, includes music, entertainment, food, arts and crafts, a plant sale, Hawaiian games and garden tours.

It will be followed by a free symposium at the East-West Center on Sept. 13 and 14 that delves into the work of the arboretum. Speakers will give short talks highlighting Lyon’s history, culture and research contributions.

Also on the agenda soon is a revamped entrance for the arboretum, funded by the Legislature and going out to bid. It will include a repaved roadway, new gate and low rock wall wrapping around the curve with large letters to let people know just what lies ahead: Harold L. Lyon Arboretum, University of Hawaii at Manoa.

“It’s a great asset,” Ania Wieczo­rek, interim associate dean for academic and student affairs at the UH College of Tropical Agriculture and Human Resources, said during a visit to Lyon with her staff last week. “We’ve got to keep it going.”