The poem is a close look at one plant, false hellebore, whose Latin name sits just under the title. Almost every line is a pair of short phrases that end in "green" and rhyme with each other. The speaker keeps circling the plant, trying one description after another, and the sounds do much of the work: "Hairy green" slides into "Scary green," and "Killing green" into "Thrilling green."
The mood shifts as the list goes on. It begins with simple, almost playful observation of how the plant looks and grips. Then words like "abortifacient," "convulsive," and "repulsive" bring in danger, because this is a poisonous plant. The speaker seems both fascinated and uneasy, drawn to the plant even while naming what it can do. "Patient green" suggests something quietly waiting.
The ending is abrupt. After "Green green," the one word "Black" cuts off the chant. The poem suggests, though it doesn't say, that this vivid life ends in darkness, or that the plant's power is something darker than its color.