noun
eightfold gardenia; Gardenia jasminoides f. ovalifolia
A double-flowered variety of gardenia. Botanical/horticultural term.
庭に八重梔子を植えた。
I planted an eightfold gardenia in the garden.
梔子 is the common gardenia (Gardenia jasminoides), while 八重梔子 is a double-flowered variety.
From 八重 (やえ, 'double, eightfold') + 梔子 (くちなし, 'gardenia').