pentadelphous

from The Century Dictionary.

• In botany, grouped together in five sets: as, pentadelphous stamens; having stamens united in five sets by their filaments, as in the linden.

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

• adjective (Bot.) Having the stamens arranged in five clusters, those of each cluster having their filaments more or less united, as the flowers of the linden.

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 five separate groups, some of which may contain a single stamen.