Actor Tim Blake Nelson has also proven himself an ambitious filmmaker—most notably in the haunting “Eye of God” (1997)—and Edward Norton is an actor who enjoys taking risks. So it shouldn’t be a surprise that their joint effort is edgy, intelligent and unusual. And also uneven. “Leaves of Grass” has so many good things going for it, though, that while you can’t overlook the flaws, you might well be willing to forgive them.

One of the best elements is that fact that Norton is given the opportunity to play two rich roles as twin brothers Bill and Brady Kincaid. They’re rural Oklahomans by birth, but Bill escaped the redneck environment to become a celebrated professor of classical philosophy at Brown, where he regales his rapt students—especially the coeds—with injunctions to take Plato and Aristotle seriously. He’s even been offered a prestigious appointment to head a new institute being planned at Harvard. Brady, by contrast, remained in Little Dixie, so called, and has become a hayseed master of pot production, with an incredibly modern facility funded by Pug Rothbaum (Richard Dreyfuss), the Tulsa-based drug kingpin who purchases all his weed.

Unfortunately, Brady’s being pressured by Pug to either repay his loan or expand his distribution network to suit Rothbaum’s needs. Deciding that he might have to deal with his boss in a way that could require an alibi, he lures Bill back home by having his partner Bolger (Nelson) inform him that Brady’s been killed. Returning for a funeral, Bill finds that Brady’s still very much alive, and intends to use his twin to impersonate him while he’s off in Tulsa dealing with Pug. And as things turns out, he needs that alibi badly.

Bill feels horribly used, of course, especially since his visit requires him to reconnect with his estranged mother Daisy (Susan Sarandon), an ex-hippie type who, though perfectly healthy, has checked into a nursing home. And his world falls further apart when he gets word from the east that he’s been accused of sexual impropriety with a student—a false charge, of course, since we’ve seen him turn down her aggressive approach, but one that threatens his career. Fortunately, there’s compensation in the form of Janet (Keri Russell), a high school English teacher who also writes poetry and seems perfect for him.

The final act goes for broke by reintroducing Josh Pais as Ken Feinman, a dentist who’s relocated to Tulsa with his family and is in desperate need of money. He’d met Bill on the flight to Oklahoma and also saw Brady looking for Pug at their synagogue. And he figures out the whole plot and comes looking for the brothers. Not only does a gun make an important appearance, but so does the crossbow that Bolger early on told Bill had killed Brady.

Like his earlier pictures, “Leaves of Grass” shows that Nelson’s a sophisticated, well-educated fellow. It’s replete with references that are rather elevated for a drug comedy—not just to Whitman and Greek philosophers, but plenty of other authors as well. But it combines that strand with one of much more ribald, earthy humor. And it adds more than a dollop of violence, which comes abruptly and unexpectedly. Both as writer and director, Nelson doesn’t manage to juggle the varied components with the tonal finesse one would wish. The picture’s lurches from laid-back comedy to black farce and extreme drama show an ambitious spirit, but it isn’t matched by equivalent dexterity of execution.

Still, throughout Norton is a joy to watch, clearly reveling in drawing two such different characters, and his enthusiasm is infectious. Nelson offers fine support as the low-key Bolger. The rest of the cast, unhappily, isn’t as strong. Sarandon can’t make very much of her underwritten role as the twin’s mother, and Dreyfuss rather flails about trying to create an indelible impression as the brutal Pug, whose presence introduces an ethnic thread that doesn’t gel. Russell is pretty much wasted in a throwaway role, and Pais goes far over-the-top. On the other hand, Nelson and cinematographer Roberto Schaefer are very successful in using their Louisiana locations to good effect, and the technical team makes the interaction between the twins an impressively seamless affair, given the modest budget.

As befits a movie about weed, “Leaves of Grass” offers quite a few hits, but unfortunately just as many misses. But if you go with the flow, you should have a reasonably enjoyable ride.