Retail company Amazon has completed a set of glass orbs filled with "cloud forest" gardens for its headquarters in Seattle, providing work areas for employees and green space for the public.

The Spheres comprises a trio on connected glass domes, located in the centre of Amazon-occupied office towers in Downtown Seattle.

Amazon founder and CEO, Jeff Bezos, officially opened the project on 29 January 2018, by giving a voice command to the company's digital assistant, Alexa.

The structure was designed by American architecture firm NBBJ, which gained approval for the project in 2013.

"This particular design was chosen due to its natural occurrence in nature and as a nod to historic conservatories, like Kew Gardens [in southwest London]," said an announcement on Amazon's blog. Similar projects also include the Eden Project in Cornwall, UK, and the cooled conservatories at Singapore's Gardens by the Bay.

In Seattle, the three glazed orbs are constructed from 620 tons of steel and supported on a thick concrete base. All three units share an open-plan indoor area that is filled with thousands of plants, which can be viewed from multiple vantage points.

Of the trio, the largest "sphere" measures approximately 90 feet (27 metres) tall and 130 feet (39 metres) in diameter. The entire structure is covered in 2,643 panes of clear glass, tessellated to form a seemingly curved surface.

The facade's geometric pattern is derived from a shape found in nature, known as a Catalan solid. Underneath the glass, a layer of film helps to limit the level of infrared radiation that enters and therefore keep the interiors cool.

Over 40,000 individual plants from all over the world fill the building, which provides work areas and meeting places for Amazon employees away from its traditional office towers in the city.

The company described The Spheres as "a direct link to nature" for employees, who can make use of a "treehouse" meeting room. The layout is guided by timber decking, floating staircases, terraces and water features, and includes a four-storey wall covered in living organisms.

"Studies suggest that spaces that embrace biophilic design can inspire creativity and even improve brain function," said Amazon's blogpost.

Other offices that are designed around plants include Italian furniture manufacturer Cassina's headquarters in northern Italy by Patricia Urquiola, the all-female co-working club The Wing in New York City, and co-working spaces by Sella Concept in east London.

Many of the plant species at The Spheres are from cloud-forest ecosystems, which are typified by cool, humid conditions. The collection includes specimens from The University of Washington and Atlanta Botanical Garden, as well as a Ficus rubiginosa names Rubi – the tallest plant inside – which was planted in California in 1969, measures 55 feet (17 metres) tall.

"The Spheres operate on a diurnal cycle – the daytime temperature inside will average 72 degrees with humidity around 60 percent, and the nighttime temperature will average 55 degrees with humidity around 85 percent," said a statement from Amazon.

The Spheres is also open year-round to the public, who can access an areas at the base of the garden called Understory, which acts as a visitor centre.

"Our goal with The Spheres was to create a unique gathering place where employees could collaborate and innovate together, and where the Seattle community could gather to experience biodiversity in the centre of the city," said John Schoettler, Amazon's vice president of global real estate and facilities.

The company has invested heavily in Seattle, reportedly adding $38 billion to the city's economy from 2010 to 2016, and is also using its home to test new ideas for the future of retail.

Earlier this month, Amazon opened a cashier-free store in the city, where customers enter via an app and simply walk out with their groceries.

The retail giant's search for a second headquarters in North America, nicknamed HQ2, has also sparked a bidding war between cities eager to entice the company and reap similar finanicial benefits.

Non-Instagram photography is by Amazon.