You gotta love Greta Gerwig: Even as the radiant mumblecore star’s Hollywood stock continues to rise, the actress remains true to her dramatic roots. In “Frances Ha,” Gerwig collaborates with co-writer/director Noah Baumbach to create a character whose unexceptional concerns and everyday foibles prove as compelling as any New York-set concept picture, delivering an affectionate, stylishly black-and-white portrait of a still-unfledged Gotham gal. With Baumbach’s help, Gerwig seems to have found the right vessel for her voice, capturing the spirit of a generation in a film whose appeal should resonate well beyond the demographic it depicts.There’s a perfectly good explanation for the pic’s title, but to give it away would spoil the last in a series of organic surprises that constitute “Frances Ha.” This modest monochromatic lark doesn’t present a story — or even a traditional sequence of scenes — so much as it offers spirited glimpses into the never-predictable life of Frances, a 27-year-old dancer still navigating the topsy-turvy post-collegiate ordeal of reconciling crazy boyfriends, flaky roommates and crushing career disappointments. That same period has fueled at least two decades of self-reflexive storytelling, from Whit Stillman’s “Metropolitan” to Lena Dunham’s “Girls” (to name two New York examples), and here brings a revitalized Baumbach back to his snappy “Kicking and Screaming” roots. Neither Frances nor best friend Sophie (Mickey Sumner, Sting’s daughter) ever picture themselves getting married. As it is, the two tentatively coupled straight white girls are quite content cohabiting in Brooklyn and living “like an old lesbian couple that doesn’t have sex.” But when Sophie decides to move to her dream Tribeca apartment with another friend, Frances is left to find a new place for herself — a fitting metaphor for the big-picture transition the barely independent young lady is facing in her life at large. According to Gerwig, in the year 2012, 27 happens to be that critical age when not-yet-adults cross the “shadow line” into maturity — a notion the well-read actress lifted from a Bildungsroman by Joseph Conrad. She and Baumbach, in designing their plausibly messy heroine, illustrate the malleability of Frances’ yet-unformed identity by shadowing her through at least half a dozen different residences. Though Gerwig toyed with a similarly rocky adjustment in rebound comedy “Lola Versus,” this livelier and more fully rounded character study benefits from the perspective a slightly older-and-wiser director brings. Along with producer Scott Rudin, Baumbach has been one of the biggest industry champions for the mumblecore set, and here, he collaborates with Gerwig (whom he first directed in “Greenberg”) on the vital detail so many of those DIY projects lack: a script. Otherwise, “Frances Ha” feels in sync with the raggedy yet sincere semi-autobiographical films surfacing these days at Sundance, SXSW and other U.S. fests. But Baumbach pushes beyond sincerity in search of truth, drawing from such stylistic forebears as the French New Wave, Woody Allen and Andy Warhol’s Factory films to capture a reality that has eluded him on his more polished dramedies. Here, it helps that he has not only chosen a lead who’s likable in spite of her flaws, but also opted to shoot this relatively inexpensive production in black and white, thereby making it that much easier for auds to consider the pic’s potentially mundane situations through the lens of Art. As the allegedly “undateable” Frances drifts from one apartment to the next — staying with a pair of rich-kid creatives (Michael Zegan and Adam Driver) one month, flying home to Sacramento the next, and even allowing for a spontaneous weekend trip to Paris — she encounters other personalities that allow the film to more fully reveal hers. “Frances Ha” isn’t a plot picture, but a portrait, after all. Where other performers act, Gerwig manages to just be, making her precisely the right young star to carry such a genial glimpse at a character who doesn’t even seem to realize she’s trying to find herself.