• Webster's Revised Unabridged Dictionary
    • a Tetradynamous (Bot) Belonging to the order Tetradynamia; having six stamens, four of which are uniformly longer than the others.
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Century Dictionary and Cyclopedia
    • tetradynamous Having six stamens, four longer arranged in opposite pairs, and two shorter, inserted lower down: a relation found only in the flowers of Cruciferæ. See cut under stamen.
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In literature:

Stamens mostly 6, tetradynamous (two inserted lower and shorter).
"The Manual of the Botany of the Northern United States" by Asa Gray