This section is from the book "The Standard Cyclopedia Of Horticulture Vol2", by L. H. Bailey. See also: Western Garden Book: More than 8,000 Plants - The Right Plants for Your Climate - Tips from Western Garden Experts.
(named after Professor Andreas Dahl, a Swedish pupil of Linnaeus, and author of "Observa-tiones Botanicae"). Syn. Georgina. Compositae. Stout perennial herbs, sometimes somewhat woody, much grown out-of-doors for the rich and profuse autumn bloom. Plate XXXIV.
Plate XXXIV. Dahlia. - Jeanne Charmet, one of the most beautiful Decorative dahlias
Tuberous-rooted (Fig. 1205): stem mostly erect, branching, glabrous or scabrous: leaves opposite, 1-3-pinnate: heads long-peduncled, large, with yellow disk and rays in a single series and mostly in shades of red and purple and also in white (in cultivation); ray-flowers neutral or pistillate, disk-flowers perfect and fertile; involucre double, the inner series of thin scales that are slightly united at base, the exterior series smaller and somewhat leafy; receptacle plane, bearing chaffy scales; rays spreading, entire or minutely 3-5-dentate: fruit oblong or obovate, strongly compressed on the back, rounded at the apex, obscurely 2-toothed or entirely bald. - Probably 10 or 12 species, in the higher parts of Mex., some of them now much modified by cultivation, and the domesticated forms often difficult of systematic study. The nomenclature of the group is confused because systematists are not agreed on the rank to be given to forms that have received independent names. Voss (Blumen-gartnerei) combines the three species of Cavanilles, D. pinnata, D. coccinea, and D. rosea, all under the name D. pinnata. His arrangement is as follows: D. pinnata, Cav.; variety coccinea, Voss (D. coccinea, Cav. D. rosea, Cav., in part.
D. frustranea, DC. D. crocea, Poir. D. bidentifolia and D. mexicana, Hort.); variety gracilis, Voss (D. gracilis, Ort.); variety Cervantesii, Voss (D. Cervantesii, Lag.); variety variabilis, Voss (D. variabilis, Desf. D. rosea, Cav., in part. D. sambucifolia, Salisb. D. superflua, Ait. D. purpurea, Poir.). It seems to be well, however, to keep D. rosea and D. coccinea distinct, and perhaps also D. pinnata; and this is the method adopted for the present treatment. Of the three Cavanillesian names, D. pinnata has priority.
Fig. 1205. Clustered roots of the garden dahlia.
A. Plant very tall, tree-like.
b. Flowers nodding, bell-shaped.
Roezl. Height 6-18 ft.: stems usually many from one base, mostly unbranched, knotty, 4-6-angled, usually dying to the ground in winter in S. Calif.: leaves 2-3-pinnately parted; leaflets ovate, narrowed at the base, acuminate, toothed, with a few short scattered soft hairs: flowers nodding, 4-7 in. across, white, more or less tinged with blood-red, especially at the base; rays sterile or pistillate, lanceolate, sharp-pointed, not 3-toothed at the apex. Gt. 1863:407; 56, p. 22. G.C. 1870:459; II. 12:437; III. 34:178. B.M. 5813. Gn. 12:352; 33, p. 527; 61, p. 40. R.H. 1872:170; 1911, pp. 62-3. A.G. 15:313. Mn. 8, p. 61 -As few conservatories can make room for so large a plant, it is common to graft this species on dwarf varieties of D. rosea. The inflated and pointed flower-buds (3-4 in. long) are very characteristic. It is not known whether the original plant collected by Roezl was found in wild or cultivated surroundings. This species and the next are mostly cult. under glass if cult. at the N., but this species thrives in the open in Cent. Calif.; the others are grown outdoors in summer, and the roots stored in winter.
Hybrids are reported between this species and D. excelsa.
bb. Flowers erect, not bell-shaped, but opening out flat.
Benth. (D. arborea, Regel). Height to 20 ft. or more: stems several from same base, usually unbranched, glaucous, marked with horizontal rings made by the stem-clasping base of the petioles as the lower leaves fall away, becoming woody for several feet in mild climates: leaves bipin-nate, as much as 2 1/2 ft. long, 2 ft. wide; leaflets as many as 25, ovate, those of the upper leaves often contracted at the base, acuminate, toothed, pale green beneath, with a few short scattered hairs or none: flowers 4 1/2 in. across, dilute purple, crimson-pink. G.C. II. 19:80; III. 27:85. - This species was described from a cult. plant with 8 rays in a single row, but with considerably elongated disk-flowers It was almost an anemone-flowered type, and all the florets were sterile. D.
arborea has never been sufficiently described as a botanical species, but plants have been cultivated for many years under this name. variety anemonaeflora, Hort. Disk of lilac or yellow tubular florets; rays flat.
aa. Plant medium, averaging 8 ft., commonly from 2-5 ft., rarely exceeding these extremes.
B. Leaves once pinnate: stem not branching from the base: habit erect. c. stem usually not glaucous: rays fertile.
D. Rays of the single flowers not recurved at the margins; of the double flowers never flat, but cupped.
rosea, Cav. (D. variabilis, Desf. D. Barkeriae and D. Royleana, Knowl. & Westc? D. superflua, Ait.
Fig. 1206. Dahlia rosea (or D. variabilis). (X 1/5)
D. purpurea, Poir. D. nana, Andr. D. crocata, Lag. D. coronata, Hort.). Fig. 1206. Leaves typically once pinnate, sometimes bipinnate; leaflets ovate, toothed, broader and coarser than in the other species. B.R. 55. B.M. 1885. - The original of practically all the old-fashioned dahlias, particularly the Single, Pompon, Show and Fancy types. It is therefore the parent of the vast majority of the horticultural varieties. This is a wonderfully variable species. Some plants are densely hairy, others scarcely at all. The leaves are sometimes bipinnate in parts of plants or throughout an entire plant. In double forms the rays usually have abortive pistils. Many garden forms have glaucous stems Some authors have doubted whether this species is distinct from D. coccinea, but the two types are very different in the garden, although there are intermediate forms in nature.
dd. Rays of the single flowers with recurved margins; of the double flowers not cupped, but long, flat and pointed, and some at least with recurved margins.
Juarezii, Hort. (D. Yuarezii, Hort.). Cactus Dahlia. Fig. 1207. Distinct in the bloom: heads brilliant scarlet; flowers irregular in length and overlapping, the rays narrow. The Cactus dahlias all originated from one plant, which was flowered in Eu. for the first time in 1864, and first pictured in G.C. II. 12:433 (1879). F.M. 1879:383. Gn. 18, p. 589; 19:742; 5C, p. 236. G.Z. 26:49.
cc. stem glaucous: rays not fertile.
Cav. (D. bidentifolia, Salisb. D. Cer-vdntesii, Lag. D. Crocea, Poir.). Fig. 1208, redrawn from B.M. 762 (1804). Always more slender than D. rosea, with narrower leaflets, and in the wild, at least, dwarfer than that species. The color range is much smaller, and does not include white or any shade of purple or crimson. The colors vary from scarlet, through orange to yellow. There are no double forms, and it has been said that this species will not hybridize with D. rosea. The named varieties pictured in I.H. 31:515 and 533 (1881), which are emphatically declared to be varieties of D. coccinea, are probably garden forms of D. rosea. The only characters that certainly distinguish D. coccinea from D. rosea are the glaucous stems and infertile rays of the former, but these characters break down in garden forms. B.M. 762. Gn. 19:154. G.C. II. 12:525.
bb. Leaves twice pinnate: stems branched from the base: habit spreading.
(D. glabrata, Lindl.). Fig. 1209, redrawn from B.M. 3878 (1841). Height 2-3 ft.: roots much more slender than those of D. rosea: stem and leaves wholly devoid of hairs; leaves bipinnate: floral bracts linear; flowers typically lilac; rays pistillate; outer involueral bracts linear. B.R. 26:29 (1840). Gn. 19:154 (1881). - This is a very distinct garden dahlia, and is worth growing merely as a foliage plant. The fine-cut character of the foliage makes it more attractive than the coarse foliage of most of the varieties of D. rosea. The plants are much dwarfer and wider spreading than most florists' dahlias, and show no stem while growing. The branched flowering stems are remarkably long, slender and wiry, often rising 2-3 ft. above the foliage. The rays are very short and often roundish, with a 6hort sharp point instead of 3 minute teeth. There are no red, yellow or white forms in nature. The roots of this and D. coccinea, being slenderer than those of D. rosea, must be preserved with greater care in winter.
D. gracilis, Ort. Leaves bipinnate and ternately divided, glabrous, the leaflets small, ovate and coarsely toothed: flowers brilliant orange-scarlet; outer bracts of involucre almost orbicular: 4-5 ft., making a dense bush with very slender growths, bearing heads 2 1/2-3 in. across. Apparently not in general cultivation - D. pinnata, Cav. Plant scarcely 3 ft. high, glabrous: leaves 5-foliolate; leaflets ovate, crenate-dentate, glaucous beneath, sessile; rachis winged: flowers large, solitary; female corolla large, blue-red, exterior involucre with 6-7 bracts, ovate, narrowed toward the base, spreading and reflexed-incurved, the interior with coriaceous lobes. The plate of Cavan-illes shows semi-double flowers, i.e. with several rows of rays, with the rays incurved at the margin and becoming at the base nearly tubular. - D. Zimapanii, Roezl, is by some retained in Dahlia and by others referred to Bidens; in this work it is described under Cosmos (C. diversifolius). Wllhelm Mlller.
L. H. B.†