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The origin of this handsome mock orange is not known, but it is probably a hybrid. It is a vigorous bush up to 10 or 12 ft high; young shoots glabrous or nearly so; bark of year-old ones not peeling. Leaves ovate or sometimes heart-shaped, 11⁄2 to 31⁄2 in. long, 11⁄4 to 21⁄2 in. wide, minutely and sparsely toothed, glabrous and glossy green above, shaggy with pale hairs beneath. Flowers faintly perfumed, pure white, cupped, a little over 1 in. across, produced during late June in leafy terminal panicles of fifteen to over twenty blossoms. Petals roundish, 3⁄4 in. long, overlapping; calyx and flower-stalk hairy; style shorter than the stamens, united just below the stigmas.
Although cultivated since before 1870, this is not much grown in gardens, although certainly one of the most attractive of mock oranges. It is distinct in its many-flowered inflorescences, combined with its glossy green leaves, its cupped flowers, and overlapping petals, and is useful in flowering well into July.
Rehder considered that P. insignis is a hybrid between P. pubescens and either P. californicus or P. cordifolius (an ally of P. californicus not treated here). Dr Hu, however, points out that matching plants occur wild in California and accepts P. insignis as a Californian native, allied to P. californicus (Journ. Arn. Arb., Vol. 37, p. 40).