Van Conner, who co-founded the legendary Northwest alternative band Screaming Trees with his brother Gary Lee and singer Mark Lanegan, has died, according to a social media post from his brother. He was 55.

“Van Conner bassist and song writer of Screaming Trees died last night of an extended illness at 55,” his brother wrote. “It was pneumonia that got him in the end. He was one of the closest friends I ever had and I loved him immensely. I will miss him forever and ever and ever.”

The Trees were founded in 1984 by the brothers with Lanegan — who died last year — and drummer Mark Pickerel in rural Ellensburg, Washington. The band purveyed a psychedelia-influenced sound that synchronized with several other indie bands from the era, particularly the “Paisley Underground” groups from California like the Rain Parade and the Dream Syndicate. After releasing several low-budget recordings on the small Velvetone label, the band signed with the indie titan SST Records and became one of the major groups of the American indie scene of the late ‘80s — which bloomed into the grunge/ alternative movement when fellow Washington State natives Nirvana took off in 1991 (Lanegan and Nirvana’s Kurt Cobain were close friends and, unfortunately, as the singer confirmed in his autobiography, drug buddies as well).

The Trees released a series of strong albums on SST, particularly “Even If and Especially When” and “Buzz Factory,” and signed with the major label Epic Records in 1990. The band released their major label debut, “Uncle Anesthesia” — which was co-produced by Soundgarden’s Chris Cornell — in 1991, but their career truly took off the following year when their song “Nearly Lost You” was included on the soundtrack of Cameron Crowe’s Northwest-scene-defining film “Singles” and the group was picked up for management by the powerhouse Q-Prime, which handled metal giants Metallica and Queensryche. The band followed with its best album, “Sweet Oblivion,” played on the Lollapalooza tour and became one of the major acts of the era.

However, longstanding tensions between Gary Lee and Lanegan increased — often resulting in physical altercations — and it was some four years before the band released another album, 1996’s “Dust.” Guitarist Josh Homme joined the band for a tour before forming Queens of the Stone Age and taking Lanegan with him.

After another long hiatus — which saw the group dropped by both Epic and Q-Prime — they recorded songs for a new album in 1999 but found no takers; the songs were ultimately released in 2011 as the “Last Words: The Final Recordings” album.

The bandmembers all went on to solo projects, with Van focusing on his band Gardener as well as contributing to Lanegan’s “Field Songs” album, along with recordings by Valis, Kitty Kitty and his brother’s solo project. Earlier he fronted a side project called Solomon Grundy, which released an album in 1990; that same year he briefly toured with Dinosaur Jr. when that band was between bassists, with his powerful and droning bass bringing a psychedelic element to the group’s sound.