Stephen Guarino, of the improv show The Nuclear Family, went a little nuts during the Saturday-night performance at the Meta Theatre. As he and his colleagues have been doing since 2007, the company of three actors (add Jimmy Ray Bennett and John Gregorio) and pianist Matthew Loren Cohen staggered through on wigs and a prayer to create a 90-minute musical theater piece off-the-cuff, sprung from the core characters of a generic American family: Mom, Dad and Daughter (some nights it’s Son). The piece and even the characters’ names are different every night, thanks to the unpredictability of audience suggestions, and the trio play different roles at each performance. Every show, however, starts in the “kitchen” — four wooden chairs, two with broken crossbeams — and spirals in and out of control from there, spinning the dual mythologies of The American Family and The American Musical around and around on a spit.

So, to get this right — not that it matters because it’ll never happen again — Guarino was playing an actress in an independent film directed by Dad (Bennett), here named George by an audience member just before the show began.

George was trying to prove to his estranged wife (named Martha by a different audience member and played by Gregorio in a wig streaked with gray), that his life hadn’t added up to zilch after all, that he could complete at least one creative project (directing a film) — and that perhaps the divorce papers she’d been goading him to sign during the play’s first scene weren’t necessary after all. Meanwhile, Martha confessed to George that she was going out on her first date in 35 years, a blind date with a man (Bennett again, in a pompadour wig), who sounded a whole lot like Christopher Walken.

Adding to the stresses of George and Martha’s marriage-on-the-rocks was their teenage Daughter (Guarino in a pigtail wig), who was in crisis because her squabbling parents rarely noticed her. (“I’m the central character,” she proudly remarked at one point.) Daughter frequently had friends over to visit, played of course by Gregorio and Bennett in yet different wigs. Daughter’s crisis was so profound that both she and the improv itself — in a terrible blow to any self-respecting central character — began to consider that she was merely an imaginary child conjured by George and Martha.

“Oh this sounds familiar, so, so familiar,” Bennett crooned in a song created spontaneously — all the songs are — as the plot progressed, no, tilted toward Albee-esque metaphysics.

So there’s George filming the scene with the actress, played by Guarino, who suddenly announces that she’s going to take off all her clothes.

Bennett and Gregorio had facial expressions that drifted from bemused to quizzical, as Guarino lowered his trousers to expose his buttocks: Is he really going through with this?

The answer became evident when Gregorio grabbed a little blond hairpiece from one of the two wig racks installed on the set, handed it to Guarino, who used it as a fig leaf as he pranced and leapt through an otherwise nude ballet, his little tummy flapping in the wind.

He made up a song, ably accompanied by Cohen, about overcoming the fear of being nude in public, how much he likes it; he knows he’s not in shape, but we should have seen him five years ago, when he was buff. Something like that.

After the show, the producers swore up and down that this was the first time Guarino had ever pulled that particular stunt.

The Nuclear Family is an Off-Broadway hit and one of two touring comedy companies that opened locally over the weekend, specializing in improvised musicals. The other, One Night Stand: An Improvised Musical, at the Hudson Guild, has much younger actors, who don’t use wigs, which is the improv equivalent of performing without a net. On the night I saw them, the seven-member ensemble concocted a father-son conflict that parodied the literary convention of young people arriving in L.A. from the hinterlands to become stars. The lanky Quinn Beswick portrayed a kid in Tennessee confronting his dad (Jonah Platt) about not wanting to live out his father’s failed dreams, about not wanting to be a star — but wanting instead to escape to L.A. to pursue his dream of cleaning up after other people who do want to be stars. (No shortage of employment opportunities in that field.) Though not as risqué or as insane as The Nuclear Family, the freshly scrubbed One Night Stand crew showed wit aplenty and boasted bona fide musical theater chops, particularly though the sharp energy and even sharper voices of Samantha Martin and Mollie Taxe. Musical Director Andrew Resnick did piano-accompaniment duties on this one.

In both shows, one of the actors opened with an introduction, soliciting suggestions for possible locales and character names and otherwise revving up the audience. This is necessary because after about 60 minutes, the structure almost invariably starts to unravel, possibly a consequence of the actors, sans script, struggling to guide it largely on the power of literary and cultural parodies and a plot that’s been roped in from the ether. Often they pull off a rescue based on a parody of a literary resolution, often not. This is pro forma in what’s become a cottage industry of “long-form improv.”

Patrick Bristow directs a monthly ­Muppet-­puppet improv show at the Avalon, called Puppet Up! Uncensored, and he also helms a company called Improvatorium, which is currently running a new 90-minute improvised show, Death Lies and Alibis, where every performance is based on the writings of Agatha Christie. Dan O’Connor has a similar enterprise going at Impro Theatre, which shares the venue with Improvatorium. Impro has a series of “unscripted” shows, aiming to capture the essences of various authors’ styles — Shakespeare Unscripted (currently playing), Tennessee Williams Unscripted, Jane Austen Unscripted, etc.

All of this derives from commedia dell-arte, a 15th- and 16th-century form of lowbrow comedy, entirely improvised by professional street clowns, and based on scenarios, caricatures and “types” familiar to Renaissance society. And if you want further derivations, commedia was spun from ancient Roman comedies by Plautus, which are believed to have been stolen (borrowed) from the texts of ancient Greek comedies that are now mere dust. There are Japanese and American cousins in Kabuki and the slapstick of the Hopi Indians, who took particular delight in ridiculing their European and American conquerers via caricatures of idiots and thieves, who spoke monologues of gibberish. The origins are actually quite murky because so little of this was written down, which has always been the point of these performances, and remains so. They’re a playwright’s nightmare, which is perhaps why commedia dell-arte fell out of favor, as European theater matured into a more erudite forms, where ideas became more dependent on specific constructions of language, which required playwrights.

Yet in the 21st century, our modern equivalent of commedia is on the rise, playing around the country at international fringe and comedy festivals to crowds younger than 30, audiences our institutional theaters are aching to get inside their own theaters. One can only speculate about the larger reasons for this phenomenon, that argumentation through reasoning via carefully chiseled words has worn out its welcome, and that parody, mockery and a theatrical insanity are the only languages that make sense anymore, or make sense to people younger than 30.

THE NUCLEAR FAMILY, presented by Need­Theater at META THEATRE. 7801 Melrose Ave., West ­Hollywood; Fri..-Sun., 8 p.m.; through August 9. (800) 838-3006.

ONE NIGHT STAND: AN IMPROVISED MUSICAL, Hudson Theater Guild, 6539 Santa Monica Blvd., ­Hollywood; Thurs.-Sat., 8 p.m.; Sat., 9:30 p.m.; through August 22. ­(323) 960-4429.

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