Spiraea douglasii Hook.
A shrub 4 to 6 ft high, forming a thicket of erect stems, reddish, covered when young with a very fine felt. Leaves narrow oblong, 11⁄2 to 4 in. long, 1⁄2 to 1 in. broad, coarsely and unequally toothed on the terminal part only, dark green above, covered with a fine grey felt beneath. Flowers purplish rose, produced in an erect terminal panicle 4 to 8 in. high, very closely packed; flower-stalks and calyx grey-downy; stamens pink, standing out well beyond the petals; ovaries glabrous. Bot. Mag., t. 5151.
Native of western N. America from British Columbia to N. California; discovered by David Douglas in British Columbia about 1827, and first raised in the Glasgow Botanic Garden from his seed. It flowers from the end of June to the end of July, and a patch several feet across makes a rather striking display. The shoots that flowered the previous summer should be pruned back in February or early March, and the plants are all the better if broken up every few years as advised in the introductory notes to this genus, and the soil enriched. It thrives especially well near water. It is allied to S. tomentosa, but differs in its glabrous ovaries, its longer more oblong leaves, and in flowering earlier.
var. menziesii (Hook.) Presl S. menziesii Hook. – Young growths and the undersides of the leaves glabrous or downy, not felted, and the inflorescence parts more finely and less densely hairy. This variety has a more northern distribution than the typical state, from N. Oregon to Alaska, and extends farther inland. Introduced in 1838. It has the same garden value as typical S. douglasii and is pruned in the same way. For the spiraeas once treated as varieties of S. menziesii, see below.
S. × billiardii Herincq – A group of hybrids between S. douglasii, or its var. menziesii, and the Old World S. salicifolia, which seem to have occurred spontaneously in many gardens from about 1850 onwards, the two species being closely akin and flowering at the same time. Here belong:
cv. ‘Billiardii’. – This, the original clone of the group, was raised by the nurseryman and breeder Billiard (sic, not Billard) of Fontenay-aux-Roses and was described in 1855.
cv. ‘Eximia’. – Leaves oval or obovate, 3 in. long, 1⁄2 to 1 in. wide, toothed in the upper half or two-thirds, underside more or less grey-felted. Panicles broadly pyramidal and much branched, the lower branches 3 or 4 in. long, leafy. Some of the finer panicles measure 8 in. long by 6 in. wide (S. menziesii f. eximia Hort. ex Zab.).
cv. ‘Triumphans’. – Leaves oval-lanceolate, 11⁄2 to 21⁄2 in. long, 1⁄2 to 3⁄4 in. wide, toothed nearly to the base, green beneath and slightly downy, especially on the veins. Panicles broadly pyramidal, branching at the base, up to 8 in. high and 4 in. wide. Flowers bright purplish rose. This is perhaps the finest of the late-flowering spiraeas, making a splendid display from mid-July onwards (S. menziesii triumphans Hort. ex Zab.).
Other hybrids of S. douglasii, of similar type to the above, have been named but are no longer in general cultivation.
S. pyramidata Greene – A shrub to about 4 ft high, spreading by suckers. Leaves usually downy beneath, oblong-elliptic to ovate-lanceolate or elliptic, coarsely toothed. Flowers white, tinged with pink in the bud, arranged in dense, broadly pyramidal to rounded panicles. This species, or perhaps natural hybrid, is intermediate between S. betulifolia and S. douglasii var. menziesii, having the habit of the former and an inflorescence like that of the latter, but shorter and relatively broader. It occurs wild in southern British Columbia, Oregon and Idaho (Hitchcock et al., Vasc. Pl. Pacific Northwest, Part 3, p. 193 and p. 195 (fig.)).