An affectionate, unexaggerated view of the American South is so rare that by featuring it, “Junebug” almost seems groundbreaking. The people in this charming, wonderful little film are ordinary Red Staters, decent folk, screwed up in their own ways and eminently real.

The setting is rural North Carolina, where a British-born Chicago art dealer named Madeleine (Embeth Davidtz) has come to court a mentally defective painter named David Wark (Frank Hoyt Taylor), hoping to get his obscene, Civil War-centric paintings into her gallery. (All the figures are painted naked, and Robert E. Lee is depicted most, um, generously.)

Coincidentally, Mr. Wark lives not far from the hometown of Madeleine’s new husband, George (Alessandro Nivola), making this the perfect chance for her to meet her in-laws. Eager to please, she memorizes their names in the car before she and George go in. She greets them with kisses on both cheeks, and she affects an immediate kinship with them. They are family, after all.

The Johnstens are unsure what to make of Madeleine. She is cosmopolitan and refined; they are down-home, blue-collar types. The mother, Peg (Celia Weston), busies herself with cooking and fussing over her family. Dad (Scott Wilson), who has the appearance of someone who is content with life, hardly says a word and spends most of his time downstairs in the woodshop. George’s younger brother Johnny (Ben McKenzie), with whom he has an ongoing feud, takes after their father for speechlessness, reading the sports page at the kitchen table and regarding everyone around him with surly impatience.

This includes his wife, George’s sister-in-law Ashley (Amy Adams), who is nine months pregnant and the exact opposite of Johnny. She bubbles with stream-of-thought chatter, her innocent, simply constructed mind flitting from one topic to the next without pausing. She instantly adores Madeleine, but you get the feeling she instantly adores everyone she meets. At her baby shower a few days after Madeleine’s arrival, Ashley greets all her guests with kisses on both cheeks.

The plot is elegantly unimportant. Madeleine woos the eccentric artist; Johnny develops a crush on Madeleine; Ashley eventually goes into labor — all the things you expect to happen, happen, but they’re not the point. What’s key is Madeleine’s discovery that her values are different from her husband’s, that life in the South is richer and more nuanced than she had realized.

But this isn’t a rah-rah, the South is awesome pep rally, either. Written by Angus MacLachlan and directed by Phil Morrison (both Southerners), it’s far more honest than that. The exaggerations you would expect to find are not here. Madeleine is citified, but not to the point of absurdity. There are no scenes of her hilariously milking a cow, or having tobacco juice spat on her, or anything like that, nor do the locals react to her like she’s some kind of space alien. The laughs in the film come honestly, not through contrivances or farce. (Those things have their place, of course, but this film isn’t about them.)

The greatest performance in the film, and one of the best performances I’ve seen all year, is Amy Adams as the pregnant, chipper Ashley. What a revelation she is! Scanning her resume at Internet Movie Database, I learn that I’ve seen her in seven movies before this one, yet I don’t remember her in any of them. And now I’ll never forget her. The character of Ashley is what you might call cinematically charismatic: the people around her barely notice her, but the movie audience can’t take their eyes off her. She’s funny, sad and unbelievable, all at once.

Perhaps her finest scene is a conversation with Madeleine. She tells her sister-in-law that she thinks the baby will change things between her and Johnny, that it will help their troubled marriage. You think, “Wow, this desperate notion that some people cling to subconsciously, she’s actually articulating it.” Then Ashley goes on to say she doesn’t really THINK it will help, she merely HOPES it does. Then she wavers some more, going back to blind optimism. The girl’s mind is an open book, and you love her for it.

Seeing the subtle ways that living in Chicago has changed George, or the way Johnny comes to life when he gets out of the house and into his warehouse job, or the comfortable marriage between Peg and her husband Eugene — these details enrich the film with both humor and sadness. Its minor flaws (Ben McKenzie’s questionable Southern accent, for example) detract only slightly, and the movie is deeply satisfying.

A- (1 hr., 47 min.; R, brief strong sexuality and nudity, some nude paintings, scattered harsh profanity.)