Terror Tuesday: The Treespasser

Do watch your step while on the castle grounds
Was good advice that Richard failed to heed.
His trespass there did not make any sounds,
And no one missed the things he took. A weed,
However, dusted pollen o'er his boots,
And that got on his hands when those came off,
And then he scratched his nose. No tiny shoots
Did sprout; 'twas all more subtle. With each cough
He gave up oxygen, soon ceased to breathe
At all. His pores grew large, for taking in
That other gas; his skin turned green; soon leaves
Replaced his hands, and roots his feet. Within,
His thoughts slowed down. Then soon all motion stopped.
Within a fortnight, Richard Tree was chopped.