The dueling-reunions aspect came together quickly. In late 2011 Mr. Morris convened a few of the band’s most significant ex-members — the bassist Chuck Dukowski and the drummer Bill Stevenson, as well as Stephen Egerton, guitarist for the Descendents — for a one-off set, and it went well. They started planning, later roping in the guitarist and hoarse-voiced singer Dez Cadena, and had a tour almost ready to announce in January this year.

But Greg Ginn, Black Flag’s lead guitarist, principal songwriter and owner of its old record label, SST, beat them to it with announcement that a new Black Flag — he has legal rights to the name — would play at the Hevy Music Festival in England. Flag rushed out its announcement of its own tour on the same day. Mr. Ginn followed with more news, of a plan to tour roughly the same markets at around the same time as Flag, as well as to release a new album of new songs.

Four months later, the Black Flag show on Saturday in San Antonio was the third in the United States after a weeklong warm-up in Europe; the Flag concert on Monday was its first in this country after an unannounced gig at the Moose Lodge in Redondo Beach, Calif. — the site, in fact, of Black Flag’s first gig in 1979 — and three dates in Europe. Both bands will continue touring through the summer; Black Flag plays two dates in Brooklyn in June, and Flag performs at Irving Plaza in Manhattan on Sept. 19.

There is some tension between the two groups. Several former members of Black Flag don’t talk to Mr. Ginn anymore; as the band’s musical director, more or less, he fired a lot of them, or made it hard for them to stay.