SEATTLE — Microsoft employees have treehouses. Apple workers have what’s been called a spaceship. And now Amazon’s staffers have a rainforest — or at least something like one — right in the middle of downtown Seattle.

On a typically overcast Monday, in a particularly Amazonian version of a ribbon-cutting ceremony for “The Spheres” — the company’s giant glass-and-metal domes filled with tropical and rare plants — CEO Jeff Bezos asked the gathered attendees to look to the ceiling. A circular blue ring lit up, and the Amazon founder summoned the company’s artificial intelligence assistant, Alexa, to officially open the building.

“OK, Jeff,” Alexa’s voice sounded, as lights switched on and misters sprayed some of the more than 40,000 plants that stock the company’s newest headquarters building.

After more than six years of planning and construction, the massive urban garden is now open for employees to hold meetings beside a cascading waterfall, brainstorm in a third-story “bird’s nest” or crack open their laptops and work amid a lush array of ferns, tropical plants and a 50-foot ficus tree nicknamed “Rubi.”

While much of the nation has been obsessed with where Amazon will build its second headquarters, the focus this week was on its hometown, where a gathering of Amazon executives and local officials appeared.

“We wanted to create a unique environment for employees to collaborate and innovate,” said John Schoettler, Amazon’s vice president of global real estate and facilities, describing the initial ideas he and Bezos had to transform the old motels and surface parking lots that populated that area of downtown. “We also asked ourselves what was missing from the modern office, and we discovered that that missing element was a link to nature.”

The striking architecture, designed by the firm NBBJ, includes more than 620 tons of steel and 2,643 panes of glass and no enclosed offices, desks or conference rooms. But the plants take center stage in the spheres, which cover half a city block downtown, sandwiched between two Amazon headquarters towers.

More than 400 species of plants, many of which are typically found in high tropical or subtropical altitudes and require cool temperatures, stock the three large domes, which come with an earthy, forest-like scent reminiscent of a botanical garden conservatory.

Asked about the choice of a tropical forest setting and Amazon’s name, the company’s senior manager of horticultural services, Ron Gagliardo, said “any connection to the Amazon rainforest is purely coincidental.”

But Gagliardo did say the space is based on data that show it’s good for employees’ well-being to be around plants and sunlight and encourages Amazon’s employees to “find their inner biophiliac that really responds to nature,” referring to a design concept based on the human tendency to seek out natural surroundings. “We get them away from their normal desk environment,” Gagliardo said. “You don’t see desks or cubicles. You kind of convene with nature.”

As the largest tech companies face a fierce battle for talent, a green-friendly building designed by high-profile architects appears to be fast replacing ping-pong tables and gourmet chef-managed cafeterias as the new must-have perk for workers.

Apple opened its “spaceship” campus, Apple Park, in April, featuring the world’s largest panels of curved glass, more than 9,000 trees and a blurring of the boundaries between nature and workspaces. Across Lake Washington from downtown Seattle is Redmond, where Microsoft recently built treehouses by Pete Nelson, host of Animal Planet’s “Treehouse Masters,” for employees to meet and work. The company also announced it was revamping its main campus there, a project that will include new biking and walking trails.

Meanwhile, Google is proposing a major new terraced complex in Sunnyvale, Calif., where employees will be able to move from one floor to the next by walking down a sloping outdoor path, as well as a new tent-like campus in Mountain View with “smile-shaped” clerestory windows and a “green loop” of indoor/outdoor spaces that wind through the building.

Facebook’s recent Frank Gehry-designed headquarters includes a nine-acre rooftop park.

“If you’re going to be in Seattle and be a programmer, the biggest options are Amazon and Microsoft,” Webb said. “They have to keep up. To me, it’s all about attraction and retention. The unemployment rate is almost at an all-time low.”