'Plant' one on me, baby.

[zombie no.one]

I think this film is the first portmanteau I ever saw (I wish they make more of them)

me too, I'm a fan of every one that I've come across....

Steve Coogan did a really good spoof of portmanteau horrors with an episode of his tv series called (appropriately enough) Dr. Terrible's House Of Horrible. The episode's called 'And Now The Fearing'

[JaseSF]

Voyage to the Prehistoric Planet had an attack sequence from a giant flytrap. The Angry Red Planet had similar as well.

[The Burgomaster]

THE RUINS (2008)
THE LONESOME DEATH OF JORDY VERRILL segment in CREEPSHOW

[etmoviesb]

Is there any movie where the Bamboo torture is shown?

[316zombie]

there's one i used to have in the blood island box, where they sacrificed sweet young things to maneating vines, i think it's called brides of blood?

[The Fake Macoy]

The villain in Men In Black 2 was a plant monster as well.

[Archivist]

The Evil Dead (1981) has some trees that make use of their, er, roots.

And the Tom Baker era Dr Who story The Seeds of Doom (1976) is a fantastically Hammer-horror style production about an alien plant pod infecting someone and turning them into a giant killer plant, known as a Krynoid.  This plant is able to telepathically control other plants, so you see many scenes of rustling foliage and masses of vine engulfing people.

The Krynoid grows at an immense pace and becomes larger than a stately home.  It's eventually taken out by an airstrike!  Meanwhile there is a psychopathic millionaire who chops up bodies in his industrial composter and wants the Krynoid to cleanse the Earth of human life.  It's pretty stern stuff for a supposed children's program!