triadelphous

from The Century Dictionary.

• In botany, having the stamens more or less coalescent in three sets: said of an andrœcium.

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

• adjective (Bot.) Having stamens joined by filaments into three bundles. See Illust. under adelphous.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective botany Having its stamens fused together at least partly by the filaments so that they form three separate groups, some of which may contain a lone stamen.