Madagascar ocotillo, Alluaudia procera, Close side view of small leaflets in patterns along a spiny woody stem, Backlit.

Madagascar ocotillo, Alluaudia procera, Close side view of small leaflets in patterns along a spiny woody stem.

Madagascar ocotillo, Alluaudia procera, Close side view of small leaflets in patterns along a spiny woody stem.

Dinosaur Back Plant, Myrtillocactus geometrizans forma cristata, Close view of spiny ribs of this unusual blue green cactus.

Dinosaur Back Plant, Myrtillocactus geometrizans forma cristata, Close view of spiny ribs of this unusual blue green cactus.

Thistle, Onopordum acanthium. Scotch or Cotton thistle single flower stem with spiny leaves, base of flower and bracts.

Cow horn, Euphorbia grandicornis. Close view of tiny yellow flowers growing along edges of spiny, fleshy leaves.

Sea holly, Eryngium x zabelii Jos Eijking. Thistle-like flower heads surrounded by spiny, silvery blue bracts.

Sea holly, Eryngium x zabelii Jos Eijking. Thistle-like flower heads surrounded by spiny, silvery blue bracts.

Sea holly, Eryngium x zabelii Jos Eijking. Thistle-like flower head surrounded by spiny, silvery blue bracts.

Cactus, Echinopsis.

Conical flower head of Eryngium giganteum surrounded by spiny, silvery bracts.? Paul Tomlins / Flowerphotos