It felt like a downbeat night at the SFJazz Center. Joni Mitchell, the guest of honor at the annual black-tie gala held on Friday, remained hospitalized, the state of her health still shrouded in mystery after she was found unconscious in her Los Angeles home more than a month earlier.

As the center's benefactors and a small assemblage of local celebrities mingled outside the building at Fell and Franklin streets, the mood on the red carpet - actually blue for this occasion - was noticeably more somber than previous years.

The windows of the vacant building across the street, meanwhile, were decorated with pictures of Mitchell at various stages of her career along with #THANKYOUJONI. A small shrine of flowers and handmade greetings adorned the chain-link fence below.

It was fitting, then, that inside the Robert N. Miner Auditorium, where the members of the SFJazz Collective and other performers had gathered to pay tribute to Mitchell, 71, the music was predominantly moody and meditative.

Journalist Ben Fong-Torres opened the program by recounting his earliest encounter with the Canadian singer-songwriter in 1969 for his first Rolling Stone cover story. "She was utterly beautiful and achingly honest," he said.

The description doesn't fit only her personality but also her songs, which traverse folk, pop, jazz, classical fusion and everything in between, making Mitchell one of the most influential and restless songwriters of the past 40 years. Then there are her words, simultaneously beautiful and absurd, sung in that unmistakable girlish soprano.

How does one even begin to interpret her work?

During the two-hour gala performance, which was recorded for Mitchell, the guest musicians approached from all angles.

Kelly Jones, a young singer-songwriter from Los Angeles, played it straight on her renditions of "Court and Spark" and "Free Man in Paris," backed by a capable band that included several of Mitchell's regular collaborators - drummer Brian Blade, pianist Jon Cowherd and pedal steel guitar player Greg Leisz.

The SFJazz Collective put a serpentine Burt Bacharach spin on "Both Sides Now," lifting the melody up, before the improvisational jazz vocalist Kurt Elling joined in, giving an unexpectedly heavy kick to "Edith and the Kingpin." Things got even heavier when he returned with the house band for a thunderous run through "The Jungle Line" that would have worked equally as well at an Imagine Dragons concert.

British singer Joe Jackson, on the other hand, drove "Big Yellow Taxi" through a New Orleans dive bar and went minimal on the infinitely more complicated "Twisted," both performed at the piano; while the country music veteran Kris Kristofferson delivered a weary, bone-dry rendition of "A Case of You."

It was the R&B vocalists who made the most of the material, embracing the torrential emotions in the songs, and confidently attacking them. First, Judith Hill, whose low-slung, soulful "River" was made resplendent with congas and wah-wah guitar; and then Patti Austin, who fully embodied "Two Grey Rooms" and "Don't Interrupt the Sorrow" with her earthy voice. Addressing Mitchell through the camera, Austin remarked, "I love you madly. Could you write some simpler songs?"

Randall Kline, executive artistic director of SFJazz, had delivered a warning earlier. "We have a very open view about jazz," he said. "Joni is impossible to classify."

Saxophonist Wayne Shorter was on hand to accept the evening's lifetime achievement award on Mitchell's behalf. Kline was also joined onstage by gala co-chairs Penny Coulter and Nion McEvoy and event planner Stanlee Gatti, who made the initial arrangements to bring Mitchell to San Francisco. "She really wanted to be here," he said. "Because she told me."

As images of Mitchell in her prime flashed on the overhead screen, the night closed out as it has the past two years: An ancient Victrola record player was wheeled onstage, the house lights were dimmed and the crackly sound of Billie Holiday's "I'll Be Seeing You" filled the room as everyone fell silent.

This time it felt just a little more poignant than before.

Aidin Vaziri is The San Francisco Chronicle's pop music critic. E-mail: avaziri@sfchronicle.com Twitter: @MusicSF