Tire industry rushes to breed special dandelions native to Kazakhstan whose taproot produces a milky fluid with rubber particles in it

FTA:

And they could have some interesting modifications. For instance, German researchers have bred the plants to grow to up to a foot (30 cm) in height, dwarfing many of their backyard cousins. They are also developing the dandelions with upright rather than flat-growing leaves - just so harvesting machines have something to grab on to.