This section is from the book "The Gardener's Monthly And Horticulturist V24", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
Botanists are now mostly agreed that the florist's Dahlias have originated from two species, D. superflua and D. frustranea, though some unite them under the name of D. variabilis - a very appropriate title, for the variation in form and color of the flowers causes them to merge into each other, and it is not easy to indicate any clear marks of distinction. The chief character, however, which has been selected for this purpose is the involucre (the bracts surrounding the flowers), which in D. superflua is reflexed, and in D, frus tranea is spreading. In other respects they are similar, having strong succulent stems, divided leaves, and flower heads in which the outer florets are flat, broad, spreading, and richly colored, the central florets being tubular and yellow. Dahlias were first mentioned by Hernandez in his account of Mexico about the middle of the seventeenth century, and two figures are given under the Mexican names, with descriptions of their supposed medicinal properties. Some years subsequently a traveler in Mexico, named Menonville, who was, it is said, "employed by the French minister to steal the cochineal insect from the Spaniards," also noticed them, commenting on their great beauty.
In 1789 plants of D. superflua were introduced to England by the Marchioness of Bute, and some were grown in Madrid at the same time, and among the latter the first one which flowered in the autumn of 1789 enabled Cav-anilles, a Spanish botanist, to define the genus under the name of Dahlia pinnata, the genus being named in honor of Dahl, a pupil of Linnaeus, and the specific title referring to the form of the leaves, and this appears to be the D superflua of succeeding authors. Two other forms also flowered in following years, and were respectively named D. rosea and D. coccinea, and all were figured in a botanical work published at the end of that century. The first plants introduced by the Marchioness of Bute appear to have been lost, and in 1804 seeds were sent by Lady Holland from Madrid to England, and plants were raised from these, which flowered in that and the following years. In Andrews' "Botanist's Repository," 1804, one of these, D. pinnati, was figured from a plant "that flowered in September and October in the open ground at Holland House, Kensington." This has large florets of a purplish crimson color, the centre being bright yellow.
In the same year a figure of D. coccinea appeared in the "Botanical Magazine," which has small bright orange scarlet flowers, and was said to have been introduced from France in the previous year by Mr. Fraser of Sloane Square. The second edition of the "Hortus Kewensis" in 1813 gives three varieties of D. suoerflua - namely, purpurea, lilacina, and nana, and only mentions another species, D. frustranea, as synonymous with the D. coccinea of the " Botanical Magazine." In this work an engraving of a single form of D. superflua appeared in 1817, together with a representation of one of the so-called double varieties, the first presumably that was figured. It has flat purplish florets, not cupped like we have them now, but full and of good form. In connection with these it is mentioned that it was the opinion of DeCandolle that "No blue variety of Dahlia superflua would ever be found, because blue and yellow being the two primitive colors of flowers, and always exclusive of each other, no blue flower ever changes to yellow, or yellow to blue." Both these drawings were made from specimens in the Comte de Vande's garden, who had imported them from France, where it appears Dahlias had then been receiving much attention for some years. - London Journal of Horticulture.