Based on the provided descriptions, Species C, the plant from Japan that grows up to a foot per day, smothers low-growing plants, kills trees, and has no natural predators, would most likely be classified as an invasive species in the United States.
Invasive species are typically characterized by their ability to rapidly spread and cause harm to the environment, economy, or human health. Species C fits this definition due to its aggressive growth and negative impact on native flora.