Cyril Ruoso / Woman with baby collecting Madagascar periwinkle (Catharanthus roseus) flowers and leaves, used in herbal medicine, and containing molecules which are used in the treatment of leukemia cancer. Berenty...

Enrique Lopez-Tapia / Spiny tree trunk (Pachypodium sp) Berenty Reserve, Madagascar.

Nick Upton / Shrubby milkweed (Gomphocarpus fruticosus), invasive species native to South Africa. Beside Rio Codula di Luna stream, Gennargentu National Park, Dorgali, Sardinia. June.

Derek Galon / Caterpillar of Monarch butterfly (Danaus plexippus) feeding on seed pod of Bloodflower plant ( Asclepias curassavica). Dominica, Eastern Caribbean, Lesser Antilles. Focus stacked photo.

Derek Galon / Seeds of Bloodflower plant (Asclepias curassavica) blown by wind from their pod. Dominica, Eastern Caribbean, Lesser Antilles. Focus stacked photo.

Joao Burini / Milkweed (Asclepias mellodora), Intervales State Park, Sao Paulo, Atlantic Forest South-East Reserves, UNESCO World Heritage Site, Brazil.

Sylvain Cordier / Rose of Desert (Adenium obesum ssp Sokotran) Socotra Island, UNESCO World Heritage Site, Yemen.

Fabrice Cahez / Myrtle (Vinca minor) flowers, Vosges, France, April.

Doug Wechsler / Milkweed tiger moth (Euchaetes egle) caterpillars on Common milkweed (Asclepias syriaca) Philadelphia, Pennsylvania, USA, July.

Chris Mattison / Wax flower (Hoya serpens) close up of flowers. Cultivated plant from Himalayas.

Ernie Janes / Bushman's hat (Hoodia gordonii) Namibia.

Loic Poidevin / White swallow-wort (Vincetoxicum sp) flowers Gorges du Tarn, France, May