The dark comedy "Flower," about a teenage girl who's too sexually advanced for her own good, opens memorably with the 17-year-old Erica (Zoey Deutch) servicing the local sheriff in his car, wherein she cheerfully blackmails him for cash in return for her not posting incriminating photos on the internet.

How else is she supposed to raise money to bail her deadbeat dad out of jail?

It's an audacious start to this often-smart movie, which doesn't have a dull frame in it, thanks mainly to the star-making performance of Deutch ("Everybody Wants Some"), who dazzles the screen with her mix of humor, sensuality, volatility and vulnerability.

Erica, who has an unapologetic talent for oral sex and a love of drawing penises, runs into unexpected turbulence when her permissive mother (a very good Kathryn Hahn, "A Bad Moms Christmas") allows her new boyfriend's unbalanced son Luke (Joey Morgan, "Scout's Guide to the Zombie Apocalypse") to move in.

The best thing that Erica can say about Luke, fresh out of rehab, is that the overweight youngster doesn't smell as bad as she expected — though her feelings for her potential stepbrother soon get complicated.

Writer/director Max Winkler (who has worked mostly in TV, including directing episodes of "New Girl") keeps things moving along briskly, and when he concentrates on Erica and her strange family dynamics, his film is a refreshingly wry (if brutal) commentary on our societal mores regarding adolescent sexuality. Rarely do American movies stray into such risky territory, particularly with dark humor.

Yet, Winkler (son of Henry Winkler) overdoes things with implausible story machinations in the second half, and the film's confidence gets a bit shaky. Even Erica gets stranded, both literally and figuratively, though Deutch is such a good performer that we stay engaged.

"Flower" is clearly not everyone's idea of a bouquet, but it's willing to take chances — and push buttons. It's a film that reflects our times, even if it makes us uncomfortable to acknowledge it.