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A shrub up to 12 ft high, with erect stems, the year-old bark brown and peeling; young shoots ribbed. Leaves ovate to oval-lanceolate, broadly wedge-shaped or nearly rounded at the base, distantly toothed, 11⁄2 to 4 in. long, 5⁄8 to 2 in. wide; glabrous except for a few hairs on one or both surfaces and on the leaf-stalk, which is 1⁄6 to 1⁄3 in. long. Flowers yellowish white, heavily scented, about 1 in. across, produced in terminal racemes of five to nine blossoms. Petals oval, 3⁄8 in. wide; calyx-lobes downy at the margins, the tube and flower-stalk either glabrous or slightly downy; styles separated at the upper third.
Native of S.E. Europe and Asia Minor; cultivated in Britain since the 16th century, probably before. It flowers in early June. This is the best-known species of mock orange in gardens, but is not in the first rank. The fragrance of its flowers is pleasing out-of-doors, but may become too insistent if the plants are numerous or near sitting-room windows. The odour is too strong for the flowers to be enjoyed in a cut state indoors. Over three hundred years ago Gerard, the herbalist, wrote:
‘They have a pleasant sweete smell, but in my judgment troubling and molesting the head in very strange manner. I once gathered the flowers and laid them in my chamber window, which smelled more strongly after they had lain together a few howers, but with such a pontick and unacquainted savor that they awaked me from sleepe, so that I could not take rest till I had cast them out of my chamber.’
Hu accepts P. caucasicus Koehne as a species distinct from P. coronarius, but it is questionable whether it deserves this rank; indeed it is not clear what constant character there is to separate it from the variable P. coronarius. This Caucasian and Armenian philadelphus is in cultivation from a collection by Roy Lancaster in 1979 above Novy Afon on the northern Black Sea coast.
According to Hu, P. coronarius ‘Aureus’ belongs to P. caucasicus on the grounds that it differs in the key-character of a pubescent floral disk against glabrous in P. coronarius.