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The Rose Flower: Its Petals and Forms (shapes)
By Dan Mills, Consulting Rosarian

This may seem like a boring subject, but it’s not when you get into it.  When you grow a variety of roses, you can’t help but be fascinated by the different flower forms (shapes) and especially the differences in petal shapes, petal textures, and petal arrangements (configurations) within the flowers.  But in researching flower form and petals you might be surprised by the apparent lack of detailed writing on the subject.  
For example, in searching the Cumulative Index of the American Rose Annual, 1916 - 1997, I found only one article specifically dealing with flower “form” and none specifically dealing with petals.  This was especially odd to me since the period 1916-1997 covers most of the evolutionary period of the classic hybrid tea form ( “…a bloom gracefully shaped with petals symmetrically arranged in an attractive circular outline tending to a high center.”, quoted directly from the ARS Judges manual).  There are a few websites, including ARS, that deal with rose flower forms, but all that I’ve seen are highly simplified and contain relatively little detail.   The one exception is the website, which claims to describe over 44,000 roses and has an excellent section on bloom form.
Nevertheless, I have pieced together information from various sources to go along with my personal experiences to develop a program of pictures to illustrate the basic flower forms and the wide variety of petal characteristics that help define those forms.  I want to extend a big “thank you” to Jean Stream for collecting, tagging, and assembling those photos into a power point program that I can share with you.     
Basic Flower Forms (shapes)

In its publication Ultimate Rose (2000, p. 157), the ARS lists the following nine rose shapes with brief definitions:
Blown: normally well-shaped bloom past its best; opened wide to reveal stamens and the rest of the center.                     
Flat: shallow low-centered bloom with a small number of petals.
Globular: bloom possessing many petals forming a ball-like flower with a closed center.
High-centered:  classical shape of the hybrid tea – long inner petals forming a central cone.
Open-cupped:  bloom possessing many petals forming a cuplike flower with an open center.  
Pompon: rounded bloom with many short petals regularly arranged.             
Quartered: inner petals arranged into four distinct sections rather than forming a cone.
Rosette: flat, low-centered bloom with many short petals that are regularly arranged.   
Split-centered:  inner petals confused (not regularly arranged), forming an irregular central area.  

Each of the forms (shapes) defined above, except Blown and Split-centered, is reiterated in the 2018 ARS Handbook for Selecting Roses on page 11.  This grouping of forms seems to encompass most OGRs and modern roses except for perhaps some of the English-style roses.  
In his book, The English Roses (2005), David Austin specifies “shallow cup” and “deep cup” as distinct forms, in addition to the ARS Open-cupped form.  His point is that most of his cup shaped roses, whether deep or shallow, are filled with petals in the center as opposed to the ARS Open-cupped form being defined as having an open center.  
Actually, David Austin specifies ten flower shapes on his website and in his printed catalogs.  He adds “single” roses and “semi-double” roses as distinct shapes. But it could be argued that it’s a moot point because both single and semi-double roses fit nicely into the ARS form called Flat.   Another slight difference is that Austin seems to consider “quartered” to be a sub-class of “rosette”, probably because many full-flowered Austin roses are basically rosette with a smaller number being clearly quartered.  A more substantial difference is that Austin considers “recurved” to be a distinct form because, in so many of his roses, the interior petals reflex (turn outward) as they age forming a ball or dome-like appearance. But the major difference, as explained above, is Austin’s addition of “shallow cup” and “deep cup” to the list of basic forms. I will attempt to illustrate clearly all of these flower forms in the power point presentation.     
Petal Characteristics

Petal count is a measure of the fullness of the flower.  ARS designates 4-8 petals as a single; 9-16 a semi-double; 17-25 a double; 26-40 full; 41 + very double.  As mentioned before, David Austin considers “single” and “semi-double” to be so different in appearance from full roses that he designates them as distinct flower forms.

Petal shape refers to the architectural detail of the petal.  Most petals are somewhat oval or wedge-shaped, with outer edges varying from smooth, to scalloped, to ruffled or frilled, to undulating, to wavy, to serrated, to pointed (sometimes called quilled).  The adjectives to describe these shapes can get dizzying, but are largely attributable to descriptions provided by rose breeders, themselves, or by companies trying to market the particular characteristic.  In almost all roses, except maybe singles, petals typically reflex inward or outward, or sometimes both ways, with respect to the center.  And the degree and direction of the curvature may vary considerably as the flower opens.  

Petal texture refers to the thickness and surface variation of the petal. Some petals are very thin and delicate (almost translucent) and silky to the touch, while others are thicker, firmer, and perhaps leathery or velvety to the touch. Most petals have a smooth surface, but some rugosa petals in particular seem to display a degree of roughness. All of these characteristics of texture are generally much easier to observe and appreciate in the garden or on the grooming table than from photographs.  Another aspect of texture worth mentioning is the petal’s relative degree of turgidity or droopiness, called “substance”.  A well-hydrated rose usually displays good substance, a concept very important to the exhibitor.

Petal arrangement is perhaps the single most important factor in defining a flower’s form.  It refers to the distinct pattern that emerges from the collective positioning of all the petals. That’s why most of the flower forms discussed above take the name of the pattern that defines them.  Some common petal arrangements are flat, cupped, rosette, quartered, spiraling to a high center, globular, button eye and imbricated.  The objective of my power point program is for everyone to come away with a clearer visual image of the various rose flower forms and the petals that collectively create them.  

Additional reference:   In addition to the books Ultimate Rose and The English Rose, cited earlier, I would highly recommend Tea Roses: Old Roses for Warm Gardens (2008).  This latter reference contains a statement of both flower size and shape, and petal shape and texture for each of the approximately 60 tea roses cataloged.  The book also contains perhaps the best rose glossary I’ve found other than the one on the website.  
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