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An evergreen, mostly stemless shrub, producing from a rootstock a hemispherical rosette of much crowded leaves up to 6 ft in diameter. Leaves 1 to 3 ft long, 1⁄2 to 11⁄4 in. wide at the base, terminated by a sharp slender spine, margins very finely toothed; the whole leaf is rather glaucous. Flowers pendent, fragrant, closely packed on the upper part of a perfectly erect, stout stem 8 to 15 ft high and 3 to 5 in. in diameter at the base; the inflorescence itself as much as 7 ft long and 1 to 2 ft wide. The six segments of the perianth are ovate-lanceolate, pointed, greenish-white tipped and edged with purple, more or less incurved, and give the flower a diameter of 21⁄2 to 3 in. Bot. Mag., t. 7662.
A native mainly of southern California, in the coastal ranges south of San Francisco, extending inland to the borders of the Mojave desert; also reported from the Mexican State of Baja California and from Arizona. It was known to the Spanish missionaries in California, but was first described from specimens collected during Lt Whipple’s exploration for a railway route from the Mississippi to the Pacific in 1853-4. Y. whipplei is a splendid species, surpassing all other yuccas, Sargent remarks, in the height and beauty of its panicles. ‘From day to day the waxen tapers on the distant slopes increase in height as the white bells climb the slender shafts. At length each cluster reaches its perfection, and becomes a solid distaff of sometimes two – yes, even six – thousand of the waxen blossoms’ (Mary Parsons, The Wild Flowers of California (1904), p. 70).
Y. whipplei first flowered in Britain, under glass, with Mr Peacock at Hammersmith, in 1876. So far as is known, its first flowering in the open air in this country was with Mr Fletcher at Aldwick Manor near Bognor in 1910 (Gard. Chron., Vol. 51 (1912), Feb. 17, supplementary illustration and p. 106); the plant had been received some six or eight years earlier. A very magnificent example flowered with W. M. Christie at Watergate near Chichester in 1921 (Journ. R.H.S., Vol. 47 (1922), fig. 23).
Y. whipplei is nearly hardy, and probably more plants have been killed by winter wet than by frost. At Bodnant in North Wales, where it has flowered several times, the plants are given no more than overhead protection in winter, to keep rain out of the crown. But all the recorded flowerings of Y. whipplei in Britain are from gardens near the south or west coasts. Yuccas need warmth in late summer and autumn if they are to form their embryonic flower-spikes and it may be that Y. whipplei needs more warmth than most other hardy species at that time. A plant at Borde Hill in Sussex vegetated for thirty years before flowering, which at least says something for its hardiness. At Bodnant, however, a plant from home-raised seeds set in 1944 flowered in 1951.
In its typical state Y. whipplei is monocarpic, i.e., the whole plant dies after flowering, and it seems that most plants grown in Britain are of this nature. Fortunately this species is self-fertile and produces good seed in this country, though artificial pollination is advisable, to secure a good set. But some wild plants are perennial and the following varieties or subspecies of these have been distinguished:
Y. w. subsp. caespitosa (M. Jones) Haines
Y. w. subsp. intermedia Haines
Y. w. subsp. percursa Haines