Ben Whishaw, right, and Emily Beecham star in “Little Joe.” (Christa Amadea/Magnolia Pictures)

Rating: (3 stars)

What’s so great about feeling happy all the time?

In the movie “Little Joe,” an allegorical art-house horror film about a genetically engineered flower whose scent has been designed to work on humans like an airborne antidepressant, that simple, even simplistic, question gets a stylish, nuanced and deeply unsettling airing. Aided by the ever-so-sightly futuristic production design of Katharina Wöppermann — who fills the film with sterile hothouse settings lit by artificial grow-lights and populated by plant biologists in white lab coats and face masks — and abetted by the disquieting sound design of Erik Mischijew and Matz Müller, who layer jarring sound effects — is that a pack of barking dogs? — over music lifted from the 1971 album “Watermill” by the late Japanese composer Teiji Ito, the movie insinuates itself into the subconscious like a metaphorical “Invasion of the Body Snatchers.” The pod people here aren’t zombielike doppelgägers who have replaced us. They are us, only new and improved.

Or so we tell each other.

The woman at the heart of the story is botanist Alice Woodard, played with a serene intensity that gradually gives way to alarm by Emily Beecham, who won the best actress prize at Cannes for her performance. Alice, a single mother, has designed the titular potted plant, dubbed Little Joe after the name of her teenage son (Kit Connor), to whom she ill-advisedly brings home a sample of the bright red bloom. It isn’t long before Little Joe exhibits behavior suggesting it contains trace amounts of the DNA of Audrey, the malevolent, man-eating plant at the center of “Little Shop of Horrors.”

From left, David Wilmot, Phénix Brossard, Emily Beecham and Ben Whishaw in “Little Joe.” (Magnolia Pictures)

Oh, it doesn’t actually devour anyone.

Directed by Austrian filmmaker Jessica Hausner, making her English-language debut with a screenplay she co-wrote with Géraldine Bajard, “Little Joe” is a tale of exquisite refinement, not heavy-handed horror, always walking that thin line between implication and doubt. Little by little, Alice starts to notice, or perhaps merely imagine, barely perceptible changes in her son’s demeanor — changes that parallel subtle shifts in her work colleagues’ personalities, most notably that of her Little Joe co-creator — and secret admirer — Chris (Ben Whishaw). The plant, in a sense, is the child of Alice and Chris.

Have Chris and Joe changed, maybe as the result of an infection introduced by Little Joe’s GMO pollen — which explodes with tiny, smokelike clouds and barely audible sighs — or has Alice? Little Joe, which has been designed to be sterile, can only ensure its survival if it enlists the help of humans. Is it secretly recruiting people — an army of complacent drudges — to act as its protectors and propagators?

It could probably use the help.

Alice starts to worry that she has created a monster that should be destroyed. Of course, we’re invited to take this thriller less than literally. It’s not a story of Man vs. Nature, except as a cautionary tale about our dependence on mood stabilizing chemicals that, in the film’s view, have destroyed our ability to truly feel things, both pain and joy.

That’s Hausner’s point. But if “Little Joe’s” message is never less than apparent, it avoids hitting you over the head with it. It’s a movie that grows on you, planting a seed that only comes to flower long after the closing credits.

Unrated. At Landmark’s E Street Cinema. Contains obscenity and creepiness. 105 minutes.