This is a barrel cactus which grows slowly and becomes up to 80cm in height and 50cm in diameter.   The stem is bright green and has prominent ribs.

Unlike many plants belonging to the family Ferocactus, Osai-maru has a needle-like spine.   At the beginning, the spine is gold but it is gradually discolored to ivory.   The Japanese name Osai-maru, meaning cactus colored yellow, comes not from the yellow color of the flower but from the color of the spine.   Young Osai-maru has five, six or more spines on the areole but when it ages, the number of spines on the areole decreases to one or two and the areole sometimes becomes spineless.

Osai-maru produces the flower relatively early and it blooms when Osai-maru becomes more than about 12cm in diameter.   The flower is brilliant yellow in color and becomes up to about 10cm in diameter.

In Higashiyama Botanical Garden, the label is written Osai-maru, which is the name when it was planted there, but the name of present mainstream is osai-gyoku.

This species is listed in Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) appendix 2.

Classification: Cactaceae Ferocactus
Scientific name: Ferocactus schwarzii G.E.Linds.
Japanese name: Osai-maru (Osai-gyoku)
English Name: ---
Native locality: Central Mexico and northern Sinaloa, Mexico
Ecological description: ---
RDB : ---
Planting place: South and Central America Greenhouse
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