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Remove a leaf, including the petiole. Place on moist medium tentacle-side up. Wait.
You may also put them in a glass of water. Roots also work well.
Root cuttings work best from D. capensis. Snip off some of the healthy roots (usually black with white tips). Snip them up into 2 inch bits. Lay them out on some media (CP mix). Cover with about 1/2 inch off more media. Keep it moist under bright lights and in a few weeks plantlets should appear.
I still need to know if you need to have the petiole for leaf cuttings, though.
Does the leaf have to be healthy and have dew?Would those old leaves work for leaf cuttings?