icosandria

from The Century Dictionary.

• In botany, the twelfth class in the Linnean system of classification, distinguished by having twenty or more stamens inserted on the calyx, as in the rose family. The plants in this class produce the most esteemed fruits.

from the GNU version of the Collaborative International Dictionary of English.

• noun plural (Bot.) A Linnæan class of plants, having twenty or more stamens inserted in the calyx.