An evergreen shrub of loose straggling habit; young shoots and leaves glabrous. Leaves oval-oblong, rounded to shallowly cordate at the base, rounded and mucronate at the apex, 3 to 7 in. long, 11⁄4 to 23⁄4 in wide, dull green above, rather glaucous beneath; stalk 3⁄4 to 11⁄2 in. long. Truss composed of six to eight flowers which are fragrant. Calyx small, 1⁄3 in. wide, with shallow rounded lobes; flower-stalk slightly glandular, 1 to 13⁄4 in. long. Corolla 3 to 31⁄2 in. wide, funnel-shaped at the base, seven-lobed, the lobes spreading, notched in the middle, white flushed with rose and glandular outside, blotched and stained with red inside the funnel. Stamens fourteen to sixteen, of unequal length, their stalks white and downy at the base; anthers pale brown. Ovary and style glandular. Bot. Mag., t. 8841. (s. and ss. Fortunei)
This species was introduced to Kew in 1889 from the Jardin des Plantes, Paris, where it was raised by seeds collected by Delavay in Yunnan. It came as R. decorum and remained under that name until the true R. decorum of Wilson's introduction flowered and showed the differences. The real R. decorum, as is now well known, is a sturdy, compact bush; R. serotinum is so lanky and so loth to branch that a plant was trained up a pillar at Kew as a sort of climber. The blotch at the base of the corolla and the reddish stains are further distinctions. Lastly it flowers in September, a fact which explains its specific name. Otherwise the two are very much alike in their blossom. It is quite hardy and gives a noble truss of blossom as the figure above quoted shows.