Classifying Dahlias: Singles, Cactus, Decorative, and Peony Forms

Originally published as The Evolution of the Dahlia: Chapter Three (1920)

Original text by J. J. Broomall is in the public domain.

Compilation, editorial notes, introduction, biography, and revised text copyright © 2026 by Steve K. Lloyd. All rights reserved.

In Classification, Broomall turns from questions of cultivation and heredity to a different problem: how an increasingly diverse flower should be named and divided into classes. His concern is not taxonomy in the modern botanical sense so much as practical classification by visible form. Singles, Collarettes, Shows, Fancies, Pompons, Cactus, Decorative, and Peony dahlias all become examples of a system struggling to keep pace with the plant’s increasing variety.

The chapter is also argumentative rather than merely descriptive. Broomall challenges contemporary definitions of the Cactus Dahlia, objects to the term “Hybrid Cactus,” and criticizes the increasingly elastic Peony class. Much of his disagreement arises because class names were being asked to convey several different things at once: flower shape, ancestry, historical naming, and exhibition convention. His later 1931 essay, Rethinking Dahlia Classification: Cactus, Peony, and the Problem of Names, would return to these problems with a substantially more elaborate system, but that later development remains separate from the 1920 chapter.

Unlike Chapters One and Four, Classification contains no explicit chapter-to-chapter promise or revision dependency in its retained prose. Its placement here is therefore editorial rather than dictated by the surviving serial sequence. 

The text printed here is from J. J. Broomall’s 1920 Dahlia Guide. 

The ever-increasing diversity in the form of the Dahlia, while adding to its popularity, is making the correct classifying of the different varieties a more and more difficult task.

There are many dahlias hard to classify; hence the overlapping of classes. Some that are classed as decorative might more correctly be described as show dahlias, and “vice versa,” and some dahlias vary in form from year to year; take the decorative dahlia Altadena for instance. When first introduced, this variety was a true decorative in form as shown in the cut, but in succeeding years the petals have become more pointed until it might be called a hybrid cactus in shape.

First in order comes the single dahlia, as that was the original form of the flower in its native habitat. The true single dahlia consists of 8 petals evenly arranged around a central disk.

I have seen varieties with 10 petals, but such are comparatively rare; in no case should there be an odd number of petals; a dahlia having 9, 11 or a greater number of petals is not a true single, and is almost certain to become duplex, or semi-double in character.

The Collarettes (which were introduced by M. Rivoire of Lyon, France, several years ago) are similar to the singles in form, but have an additional row of much smaller petals located at the inner base of the larger outside petals; these inner petals are generally of a different color, but not always.

In the variety called swallow, the outer petals and collar are both pure white. There is also a variety that is pure yellow throughout, but in most of the yellow varieties the collar is lighter in color.

The “Show Dahlias” are compact double flowers composed of a large number of rather short tubular petals. A. D. Livoni might be considered a perfect sample of this class.

Fancy Dahlias differ from Show Dahlias in color only, the majority of them being really variegated Show Dahlias.

Pompons are diminutive Show and Fancy Dahlias, the only difference being in the size. A Pompon should not exceed two inches in diameter; some growers will probably place the limit at less than that.

And now we come to the Cactus Dahlia; if I am correctly informed the American Dahlia Society accepted the decision of Prof. F. H. Hall, of the N. Y. State Experimental Station, as to what should be considered a true Cactus Dahlia, and that no Dahlia having petals less narrow and pointed than J. H. Jackson should be classed as a Cactus Dahlia.

Now while I have corresponded with Prof. Hall for years, and respect him as a Horticulturist, and a gentleman, I cannot agree with his ruling. I claim that any dahlia that is as narrow and pointed as Juarezi is a Cactus Dahlia and cannot correctly be classed as a Hybrid.

Here is a picture of Juarezi, the Original Cactus Dahlia; it is from a poor photograph, but it shows the form of the flower. I have been growing it for more than 20 years and have never seen it more pointed or narrow than this.

I overheard a Teacher of Horticulture in my garden last summer declare that the “Golden West” could not be considered a Cactus Dahlia; I showed him Juarezi and asked him how he would classify that; he replied, “it is a Hybrid Cactus.”

Now Hybrid is defined as a mongrel—“a mixture of two species.” Poor Juarezi, it would appear bad enough to have been thrust almost into oblivion by its gorgeous descendants; but to be called a mongrel—this is too much.

According to history Juarezi was called a Cactus Dahlia because it resembled the blooms of Cereus Speciossimus in COLOR, and not on account of the shape of the flower. It does seem to me that those judges who refuse to accept any Dahlia as a Cactus Dahlia unless it has needle-like petals are liable to “swallow a camel while straining at a gnat.”

Hybrid Cactus; this term, while it may give an idea as to the form of a certain class of Dahlias, as applied to a great many at the present time, is both erroneous and absurd.

Decorative Dahlias; a true Decorative Dahlia should have rather broad, flat petals, showing no tendency to become either cupped, quilled, or pointed. Minna Burgle, and Hortalanus Fiet can be considered perfect samples of this class.

Peony Dahlias; if we find the Cactus and Hybrid Cactus somewhat “mixed” in the Peony class is confusion worse confounded.

I remember a good many years ago, soon after the first of this class was introduced from Holland, of sending for the first set of 8 or 10 offered, having no idea at the time what a Peony Dahlia was like; great was my disappointment when I found I had purchased a lot of semi-double decoratives, for that is exactly what they were.

I never could understand why the term Peony was applied; possibly some of them may have borne a faint resemblance to P. Moutan, the semi-double tree peony, but I have yet to see a Peony Dahlia that bore the least resemblance to the old-fashioned Peony of the gardens back home.

While the first of this class were decorative in form, what of the Peony Dahlias being offered today? Apparently every open-faced Dahlia of every conceivable shape, and some with no shape at all have been put into this class until it promises to rival the “Smith family” in numbers.

Now there are some very beautiful semi-double dahlias that are a joy to look at, and well worth growing; but why not confine the Peony class to those decorative in form, and if the flower happens to be a semi-double Cactus or Hybrid Cactus, call it such, and not class it as a Peony when it bears no more resemblance to a Peony than it does to a Rose or a gilliflower.

1. Classification and petal number. Broomall’s categories reflect the horticultural and exhibition terminology of his period rather than modern botanical taxonomy. His statements that a true single dahlia has eight petals, that an odd number of petals disqualifies it as a true single, and that such flowers are almost certain to become duplex or semi-double are preserved as part of his historical understanding of dahlia form.

2. F. H. Hall and the Cactus Dahlia. Broomall reports, with the qualification “if I am correctly informed,” that the American Dahlia Society had accepted Prof. F. H. Hall’s standard for defining a true Cactus Dahlia. Broomall rejects that standard and argues instead from Juarezi, the original Cactus Dahlia as he understood it. The passage records Broomall’s side of a contemporary classification dispute and should not be read as an independently established account of the Society’s formal position.