The Aril Society Checklist

 by Tom Waters

When I'm not writing blog posts, one of my many other iris-related activities is serving as checklist editor for the Aril Society International. I've just completed the 2023 update of the checklist, which is available on the ASI website. It occurred to me that there are probably many people who are not aware that the ASI maintains a checklist of aril and arilbred irises, nor aware of what it offers beyond other references. So I thought I would use this blog post to have a look at the checklist and why it is important.

When the Aril Society International was formed in the 1950s, there were no standardized definitions for the various types of aril and arilbred irises. Irises with oncocyclus or Regelia ancestry were registered with the American Iris Society under a bewildering range of classification codes. One of the first tasks of the new society was to sort through all the various registrations and establish specific categories for them. A persistent problem in the early years was that irises of 1/8, 1/16, or even less aril ancestry were being given awards as arilbreds despite being indistinguishable from TBs. The society addressed this by requiring irises to be 1/4 aril or more to be considered as arilbreds. Subsequently, there were two separate award systems created: one for arilbreds of 1/4 to 1/2 aril content, and another for irises of 1/2 aril content or more.

'Loudmouth' (Rich, 1970) won the
C. G. White Award as an OB (1/2 aril)
but is now an OB- (less than 1/2) 
because of a change in definition.

The checklist was critical for establishing which irises met the various award criteria. The editor would take the registration data, do pedigree research, consider an iris's appearance, breeding behavior, and any chromosome counts that had been done, and then assign it to the appropriate category. In days before the internet, the ASI checklist was the only source of this classification information, because it was impractical to reprint the American Iris Society checklists to give updated classifications for arilbreds. The classifications and definitions used by the Aril Society have changed several times over the years, and the checklist is the only authoritative reference on how definition changes have affected the classification of each arilbred iris. Applying the current definitions, which involve estimating the chromosome makeup of each cultivar, is not a trivial matter in some cases.

Here are some of the things you will find in the ASI checklist that may not be presented accurately (or at all) in other sources:

Classification Information. Each iris listed, even historic irises registered long ago under other definitions, are assigned to the current ASI classification, to the extent possible given the existing information. This is of particular value to show classification committees in regions where arils and arilbreds are likely to be exhibited. It is especially important for irises that were once considered arilbreds, but no longer meet the definitions of that class.

Height Categories. In 2018, the ASI established definitions for two height categories for smaller arilbreds: arilbred dwarf (ABD) and arilbred median (ABM). These are included in the current edition of the AIS Judges' Handbook. The checklist gives the correct height category for each arilbred listed.

Chromosome Configuration. Aril and arilbred irises may include chromosome sets from oncocyclus, Regelia, tall bearded, and dwarf bearded species. Which chromosome sets are present in a given iris is of considerable interest to hybridizers, as it affects fertility and helps the hybridizer properly classify any resulting seedlings. The checklist provides the most likely chromosome configuration for most irises listed, along with an actual chromosome count where one has been reported.

Fertility Observations. When an iris is known to have produced offspring as a seed parent or pollen parent, this is noted in the checklist.

Is this 'Bronze Beauty',
'Hoogiana Bronze Beauty',
Iris hoogiana 'Bronze Beauty',
'Bronze Beauty Van Tubergen',
or 'Antiope'? Answer: yes.

Irises Not Eligible for Awards as Arilbreds. An appendix to the checklist provides a thorough listing
of irises that do not qualify as arilbreds for various reasons: never having been registered, having been registered in a non-arilbred class, or having been disqualified as definitions became more strict.

Nonregistered Aril Hybrids. A substantial number of aril hybrids have been introduced, particularly through the firm of Van Tubergen in the Netherlands, that were never registered with the American Iris Society. Some were registered with the Dutch registration authority for bulb irises, while others were simply not registered at all. The checklist includes these in an appendix, along with photographs and other information.

Even today, where so much information seems just clicks away on the internet, the ASI checklist fills an important role in providing authoritative information that is not reliably available elsewhere. It is an important resource for judges, show officials, and hybridizers. Anyone with an interest in aril and arilbred irises should become familiar with what the checklist has to offer.

In Praise of Regelias

by Tom Waters

The Regelias are a group of irises native to central Asia, their range extending from near the Caspian Sea to the mountainous regions bordering Tibet. Their nearest relatives are the oncocyclus, which are found further west and south from western Iran to the Mediterranean. Regelias and oncocyclus together comprise the aril irises.

First, a few comments on the name "Regelia". The name honors German botanist Eduard August von Regel, who was director of the botanical garden in St. Petersburg, Russia, late in the nineteenth century. Russian plant explorers of that time were very active in central Asia, seeking out new species and bringing them to attention of European botanists and gardeners. The proper pronunciation of the name is thus Reh-GEH-li-a, although most English speakers have taken to using the pronunciation Reh-JEE-li-a instead. The name should be capitalized, since it comes from a personal name. Spell-checking software likes to change the name to "regalia", which refers to Royal trappings, a blunder that one should be alert for.

Regelias are similar to oncocyclus in having a large cream-colored aril attached to the seed, in going completely dormant in summer, and in preferring arid conditions. Whereas oncocyclus iris have only one bloom per stalk, Regelias usually have two. Regelias have beards on the inside of the standards as well as the falls! Whereas many oncocyclus have large globular blooms with prominent signals, Regelias have more svelte, elongated flowers, often with conspicuous veining. The two groups are interfertile, and there are advanced-generation hybrids between them.

There are eight or more species of Regelias. Historically, the three species grown in European and American gardens were the diploid Iris korolkowii and the tetraploids I. stolonifera and Iris hoogiana. More recently, I. afghanica and I. lineata are also sometimes obtainable. W. R. Dykes regarded Iris hoogiana as the most beautiful of all irises, because of its satiny sheen and elegant form.

Iris hoogiana

Iris stolonifera

'Vera' (RH)

There are hybrids between the Regelia species, called Regelia hybrids (RH). Two widely known Regelia hybrids are 'Vera' (uncertain parentage, derived from Iris stolonifera, probably crossed with Iris korolkowii), and 'Bronze Beauty Van Tubergen', a stolonifera/hoogiana hybrid registered by the Aril Society International in 2001, but in commerce since the mid-twentieth century.


All Regelias are adaptable to a wider range of climatic conditions than their oncocyclus relatives. Here in northern New Mexico, mine persist better than daffodils, and get the same care. Cold winters present no problem whatsoever, as they are native to continental mountainous regions. Dampness and humidity in summer can cause problems, as the plants are dormant then and susceptible to rot.

Regeliocycli

'Bronze Beauty Van Tubergen' (RH)

Once it was understood that the Regelias and oncocyclus irises could be crossed readily, hybridizers became interested in such hybrids, mostly as way to breed the Regelia adaptability into the often troublesome oncocycli, which are notoriously particular and difficult to grow in many climates. The firm of Van Tubergen produced a number of regeliocyclus hybrids in the early 20th century, many of which indeed proved quite durable and are still enjoyed today. Most of these were produced by crossing Iris korolkowii with oncocyclus species, and showed both Regelia veining and oncyclus dotting and signals. In current usage, the term "regeliocyclus" (RC) refers to a hybrid with both Regelia and oncocyclus ancestry that is predominantly Regelia in appearance. In practice, regeliocycli are aril hybrids with 1/2 Regelia ancestry or more.

'Dardanus' (Van Tubergen, not registered) (RC)

Regeliabreds

When hybridizing interest in arils blossomed in the 1940s and 1950s, the attention was almost exclusively on the oncocyclus. Regelias were thought of as "poor relations" that were not always welcome at the table. The prevailing opinion at the time was that they might be useful in breeding arilbreds that were easier to grow, or to facilitate breeding oncocyclus with bearded irises, but it was the "onco look" that was the holy grail of arilbred breeders, and signs of Regelia ancestry were frowned upon.

'Stars Over Chicago' (H. Danielson, 1973)

Henry Danielson was among the first to produce and promote arilbreds of purely Regelia ancestry, launching a popular series of regeliabreds with 'Genetic Artist' (H. Danielson, 1972). These regeliabreds (RB) were derived mostly from I. stolonifera and I. hoogiana. Rather than the globular oncocyclus look expected of arilbreds at the time, they tended toward elongated, open form, showing off the often dramatic colors of the insides of the standards. Although I. stolonifera itself tends to brownish and muted violet tones, its arilbred descendants often combine gold or yellow color with lavender or electric blue flushes in the center of the falls and standards, with similarly colored beards. These unconventional arilbreds were welcomed enthusiastically by some, but reviled by others as garish departures from the oncocyclus ideal.

In the 21st century, French hybridizer Lawrence Ransom picked up the torch of regeliabred breeding, using the Regelia hybrid 'Vera' to produce the siblings 'Eastern Blush' (2002) and 'Eastern Dusk' (2010). 'Eastern Dusk' then gave the distinctive horned arilbred 'Poisonous' (Ransom, 2010).

'Poisonous' (RB-)

Ransom also produced a delightfully varied series of regeliabred arilbred medians, again using 'Vera' as the Regelia parent, with mixed SDB pollen. These "Vera girls" include the widely grown 'Vera-Marina' (Ransom, 1998) and 'Vera-Ruby' (Ransom, 1996).

A special favorite of mine is an arilbred dwarf regeliabred from I. stolonifera X I. pumila, 'Topaz Talisman' (Jensen, 2015), from long-time Regelia enthusiast Elm Jensen, registered at 10 inches in height.

'Topaz Talisman' (RB)

Regelias and their regeliabred descendants have attracted a devoted following over the years, and have shown their great potential in adding variety, interest, and ease of culture to a collection of arils and arilbreds. Much of their full potential, I believe, is still untested. For decades, they have suffered from unfair comparison with their more popular oncocyclus and oncobred cousins. As more growers and hybridizers move away from the prejudices of the past, the Regelias and regeliabreds may at last come into their own as fascinating and beautiful types of iris in their own right.

An Arilbred Iris Sampler

Tom Waters

'Oyez' (White, 1938)

I was recently contacted by an iris lover who had read my blog post on the classification of arilbred irises and wanted to sample each of the categories. She asked if I had any recommendations. I gave a few off the top of my head, and she suggested that this might make a good blog topic. I agree! So here is my arilbred sampler, for those who want to try the full range of different types of arilbreds.

I've restricted the irises mentioned here to those that are readily available. The commercial gardens that have the best selection of arilbreds are Superstition Iris Gardens, Mid-America Garden, and Blue J Iris. In addition, the Aril Society International has an annual plant sale with many more arilbreds than these commercial growers offer. The offerings vary each year depending on what members contribute, but many varieties are offered nearly every year. If an iris was available from one of the three large commercial growers in their most recent catalog, or in the ASI plant sales for the last two years, I deemed it readily available. Some other commercial growers list a small number of arilbreds, and if arilbreds are grown in your area, the local iris society plant sales can also be a good source of plants.

I want to be clear that this listing is indeed intended as a "sampler". The idea is to cover as many different kinds as possible, to showcase the diversity of arilbreds. It is not an attempt to identify the "best arilbreds" by some objective criteria, nor even a list of "Tom's favorites". The idea is that if you are new to arilbreds, and plant a varied assortment, you can discover your own preferences and what grows well for you.

The ASI recognizes nine different categories of arilbred, based on the type and amount of aril content the iris has. There are two types of pure arils: oncocyclus and Regelia. An arilbred can have either or both of these types of aril in its background. Hence we have oncobreds (OB), Regeliabreds (RB), and oncogeliabreds (OGB, mixed onco and Regelia content). Furthermore, arilbreds can be half aril, more than half aril, or less than half aril. Those with more than half aril content are indicated with a "+" sign; those with less than half aril with a "-" sign. No sign is used for those that are half aril. Thus RB+ means an arilbred whose type of aril content is Regelia only, and whose amount of aril content is more than half.

It turns out that these nine categories actually allow for more distinctions than a practical gardener need attend to. There are very few OB arilbreds, and they are indistinguishable from most OGB types. The reason is that most of today's arilbreds are descended from pioneering work by C. G. White in the 1940s, and White did not keep track of parentages during this time. So his arilbreds, although drawing heavily on oncocyclus arils and selected to resemble oncocyclus as much as possible, are classified as OGB because of the possibility of some Regelia ancestry. So I don't separate OBs from OGBs here.

I do, however, separate out the arilbred medians and arilbred dwarfs from the tall arilbreds. These smaller arilbreds, typically with dwarf or median bearded irises in their parentage, fill a very different role in the garden and provide much of the diversity to be encountered in the arilbred tribe.

So much for the preliminaries. Onward to the plants!

OGB and OB (Onco-type halfbreds)

These are what most of us think of when we think of arilbreds. Most are tall types, with TB and oncocyclus ancestry dominating. Blooms are typically large and globular, often with strong aril markings, such as signal spots or veining.

'Refiner's Fire' (McGrath, 2007)

Large bold signals are actually a rather recent development in this group, with 'Energizer' (Shockey, 1996) being a striking breakthrough in its time. More recently, 'Noble Warrior' (Tasco, 2006) combines a dramatic signal with a bit of veining. 'Refiner's Fire' (McGrath, 2007) gives a striking dark signal on a deeply colored red-toned flower.

'Sand Dancer' (Tasco, 2010) gives us a whole different look, with falls covered in peppery stippling. Yet another completely different look is to be found in 'Navajo Velvet' (McAllister, 2009), with falls of lustrous, satiny mahogany red.

The historic arilbred 'Oyez' (White, 1938) has seduced many iris growers into the arilbred world with its dramatic precise veining. Strangely, it has been difficult to reproduce this striking pattern in modern arilbreds. ('Oyez' is a sterile diploid.) An early success was 'Jonnye's Magic' (Rich, 1992). For a true modern advancement in veined arilbreds, seek out 'Alakazam' (Tasco, 2013).

'Aladdin's Gem' (Thoolen, 2002)

There are few arilbred medians and arilbred dwarfs in this category. Very notable is 'Aladdin's Gem' (Thoolen, 2002), a fertile aril-pumila hybrid about the size of a small SDB (standard dwarf bearded)!

OGB- and OB- (Onco-type quarterbreds)

Originally, these categories were dominated by tall arilbreds that came from crossing halfbreds with TBs. At a time when halbreds were uncommon and difficult to grow, the quarterbreds were the most accessible arilbreds for most gardeners. The historic iris 'Elmohr' (Loomis-Long, 1942) was a fine example of the type, the only arilbred to win the Dykes Medal. It does not show the strong aril patterning we now expect in arilbreds, without signal or veining to speak of. To understand its allure, we must think back to a time when TBs were troubled with narrow petals and often droopy form. 'Elmohr' stood out with dramatically large blooms, wide falls, and a bit of globular onco form to bring it all together.

Some other tall quarterbreds for the sampler are 'Dune' (Hager, 1981) and the very recent 'Heart of Hearts' (Black, 2015). At their best, this type of iris can bring some of the modern TB form and bud count into irises that still evoke their aril ancestry.

'Desert Snow' (Black, 2013)

Since the 1970s, however, arilbred medians have increasingly dominated these categories. Crossing an
OGB halfbred with an SDB produces an OGB- arilbred median. In the garden, these occupy a niche similar to the IBs (intermediate beardeds), but with some aril traits to give them that special something extra. The charm and adaptability of this type of arilbred has given them a great appeal among arilbred growers and median fanciers alike. 'Brash and Bold' (Black, 2009) and 'Desert Snow' (Black, 2013) are fine examplars of what this category has to offer.

A somewhat different approach is found in 'Persian Sapphire' (Baumunk, 2005), a child of 'Aladdin's Gem' that has more Iris pumila in its makeup than TB.

There are some arilbred dwarfs in this category that are worthy of attention. 'Loudmouth' (Rich, 1970) is a perennial favorite, SDB-sized with raucous signal and veining and globular form. 'Tiny Pirate' (Rich, 1990) is the most diminutive arilbred I have grown; it would be small even among MDBs (miniature dwarf beardeds), but struts onco form, a signal, and a whisper of veining.

RB (Regelia-type halfbreds)

Enthusiasm for large, globular oncocylcus irises with their dramatic signals and stippling was a driving force in early arilbred breeding. The Regelias took a back seat in the minds of many growers and breeders; sometimes they were thought of as providing nothing but some ruggedness and climate adaptability. But some have always appreciated the Regelias for their svelte elegance, sometimes striking veining, satiny texture, or blended colors.

An early Regeliabred that helped draw attention to the potential of this type of iris was 'Genetic Artist' (H. Danielson, 1972). This shows a classic color pattern derived from the Regelia Iris stolonifera: a yellowish rim around a blue or violet center. 'Afrosiab' (Volfovich-Moler, 2001) shows a touch of ruffling from its TB parent, 'Mary Frances' (Gaulter, 1973). The French hybridizer Lawrence Ransom worked extensively with Regeliabreds, with his 'Eastern Blush' (Ransom, 2002) being much used in his breeding program.

RB- (Regelia-type quarterbreds)

Ransom's work takes center stage in this category. Among the tall RB- are the horned 'Sandthorn' (Ransom, 2011), and his "Pashtun" series, for example 'Pashtun Princess' (Ransom, 2011).

Ransom also produced a delightfully varied series of RB- arilbred medians, the "Vera girls", from crossing the Regelia 'Vera' (Van Tubergen, not registered) with SDBs.of which 'Vera-Marina'  (Ransom, 1998) is one example.

OGB+ (Onco-type "three-quarter"-breds)

This group has become sadly scarce in commerce, with seldom any new ones registered and introduced. This is perhaps because few arilbred hybridizers today grow the oncocyclus species and hybrids needed to produce this type of arilbred, which usually comes from crossing an OGB arilbred with a pure oncocyclus. The few that are readily available are not always representative of the best this type of breeding has to offer. 'Tul Kerem' (H. Danielson, 1974) is interesting but I find its combination of oncocylcus and Regelia traits ends up not doing justice to either. 'Masada's Glory' (Whitely, 2002) is a better exemplar of what this category has to offer. Although they do not meet my availability criteria, keep a look out from 'Jeweled Veil' (Rich, 1978) or 'Dotted Sunsuit' (Mathes, 2001). These show the oncocyclus features of their ancestry to best advantage.

RB+ (Regelia-type "three-quarter"-breds)

'Turkish Topaz' (Austin, 1962)

A couple oddities round out the sampler. 'Turkish Topaz' (Austin, 1962) was registered as a pure Regelia hybrid, but its parentage is somewhat ambiguous and it looks and grows like an RB+. The flowers are yellow with much brown streaking and blotching. 'White Arts' (L. Danielson, 1986) has only Iris hoogiana in its Regelia ancestry. This species shows nothing that we might recognize as distinctively aril in its coloration. If you walked by 'White Arts' in a garden, you could be forgiven for thinking it was a white IB or perhaps an antique diploid TB.

If you want to sample the world of arilbreds, be sure to try several different types. The variety available in plant size, color pattern, and form is truly remarkable!

Classifying Aril and Arilbred Irises

by Tom Waters

If you're even a little interested in arils and arilbreds, you will have noticed that there is a rather bewildering array of terms used to describe them in catalogs, in iris society publications, and in general use among iris growers. In today's post, I hope to help make sense of it all.

The Big Distinction

The most important distinction of all is that between arils and arilbreds. By today's definition, an aril is a species from the oncocyclus or Regelia sections, or a hybrid derived only from these two groups of species. In contrast, an arilbred is a hybrid derived from both arils and ordinary bearded irises (whether tall bearded, median, or dwarf).

Although this seems pretty easy, and these definitions have been official for more than half a century, one still often hears people casually refer to both arils and arilbreds as "arils". This creates a truly unfortunate confusion, especially since arilbreds differ from arils in both appearance and cultural requirements. To emphasize the distinction, you will sometimes hear people speak of "pure arils" to clarify that they are not talking about arilbreds.

A Closer Look at Arils

Aril hybrids are hybrids whose ancestry is only oncocyclus, Regelia, or both. A hybrid with only oncocyclus ancestry is an oncocyclus hybrid (OH), one with only Regelia ancestry is a Regelia hybrid (RH). Simple enough. But there are two terms in use for hybrids that are a mixture of oncocyclus and Regelia: regeliocyclus (RC) and oncogelia (OG). Originally, these terms indicated whether the cross used to produce the hybrids was Regelia x oncocylcus or oncocyclus x Regelia, but that turned out to be an unhelpful distinction. The appearance of the flowers doesn't depend on which direction the cross is made, and once you have advance-generation hybrids, the distinction is impossible to maintain. Today, we use RC to refer to aril hybrids where the Regelia influence is predominant (these are typically 1/2 Regelia or more by ancestry, but it really depends on the appearance of the flower, not the details of the pedigree). OG, naturally, refers to a hybrid where the oncocyclus influence is predominant.

Iris acutiloba lineolata, an oncocyclus

Iris stolonifera, a Regelia

A Closer Look at Arilbreds

Long ago, people used the word "arilbred" to refer to any iris with both aril and bearded ancestry, regardless of how little aril ancestry or aril flower characteristics it had. Today we know that inheritance is through chromosome sets, and a set of chromosomes is usually either passed on to a hybrid as a complete set or not at all. So many older "arilbreds" that were 1/8 or 1/16 aril by ancestry really had no aril content at all!

One of the first initiatives of the Aril Society International after it was formed in the late 1950s was to restrict the definition of arilbreds to irises with significant aril ancestry and significant aril appearance. Today, to be classified as an arilbred, an iris must be at least 1/4 aril by chromosome complement and the flower must show at least two aril characteristics, such as signal or veining. This definition helps protect the distinctiveness of arilbreds as a class.

Another initiative of the Aril Society was to encourage hybridizers to work with arilbreds that had more aril content and appearance. A separate category was created for arilbreds that are at least 1/2 aril, and these are eligible for a special award, the Clarence G. White Medal. Those less than 1/2 aril are eligible for the William Mohr Medal instead. Unfortunately, there is no simple terminology to distinguish these two categories; you just have to say "less than 1/2 aril" and "1/2 aril or more".

One peculiarity of this division is that aril hybrids (pure arils) are also eligible for the C. G. White Medal, because not enough of these are produced or widely grown to merit their own system of awards. I think this has contributed in a small way to the confusion between arils and arilbreds - for a number of years, the American Iris Society used the abbreviation "AR" for both arils and arilbreds eligible for the C. G. White Medal, and "AB" for arilbreds eligible for the William Mohr Medal.

Nine Types of Arilbreds? Yes, Really

Although for awards purposes, the American Iris Society sorts all arilbreds into only two classes (less than 1/2 aril and 1/2 or more aril), the Aril Society uses a more detailed system of categories that tracks not only the amount of aril content, but also the type of aril content (oncocyclus, Regelia, or both).

An arilbred with only oncocyclus and bearded ancestry is an oncobred (OB). One with only Regelia and bearded ancestry is a regeliabred (RB). If both oncocyclus and Regelia ancestry are present, it is an oncogeliabred (OGB). This is by far the largest category.

If the arilbred has less than 1/2 aril content, it is marked with a "-" sign. If more than 1/2, with a "+" sign. If it has 1/2 aril content exactly, neither a "-" or "+" is used.

So all together that makes nine types of arilbred: OB-, OB, OB+, OGB-, OGB, OGB+, RB-, RB, and RB+.

'Bhutan' (Tasco, 2010), an OGB

'Jeweled Veil' (Rich, 1978), an OGB+

A point to note is that since 1990, the amount of aril content is based on chromosome sets, not parentage (which is why the word "content" is used rather than "ancestry"). Although the distinction between chromosome content and ancestry often makes no difference, there are times when it does. 'Loudmouth' (Rich, 1970), for example, came from a cross of an oncocyclus with an SDB. Thus it is 1/2 aril by parentage. However, the oncocyclus parent was a diploid, providing only one set of aril chromosomes, whereas the tetraploid SDB parent provided two sets of bearded chromosomes, making 'Loudmouth' only 1/3 aril by chromosome content. It won the C. G. White award under the old parentage system, but today it is classified as OB-, and would not be eligible for that award.

'Loudmouth', an OB-

Despite all this attention to detail regarding the aril ancestry of arilbreds, no distinctions at all are made regarding the type of bearded ancestry, whether TB, dwarf, or median. Sometimes smaller arilbreds with dwarf or median ancestry are called "arilbred medians", "aril medians", or other similar terms, but these are not official categories.

Finally, here is a chart that tries to make sense of this all:

I hope this post has shed some light on a rather complicated subject. Do you find these categories helpful when choosing and growing arils and arilbreds?

Tetraploid Arils, Anyone?

by Tom Waters

'Tadzhiki Eclipse'

If you're a gardening enthusiast with a keen interest in irises or other perennials, you've probably come across the term tetraploid. There are tetraploid daylilies, for example, and in the iris world you'll see the term used to describe some miniature tall bearded (MTB), Siberian, and other types of iris. But what is a tetraploid and why does it matter if a variety is tetraploid or not?

Plants and animals are made up of cells, and in the nucleus of each cell are structures called chromosomes that carry the organism's genes. These chromosomes come in sets. For almost all animals and many plants, there are two sets of chromosomes in each cell. Humans, for example, have two sets of chromosomes, 23 in each set. At conception, each person receives one set of chromosomes from their mother and one from their father. One can't really think of any simpler way for an organism to inherit genes from both parents.

There are more complicated ways, however, especially in the plant kingdom. Some plants have four sets of chromosomes, two sets coming from each parent instead of one. These are tetraploids. (Plants with just two sets are called diploids.)

What are the consequences of having four sets of chromosomes instead of two? One consequence is that tetraploids are frequently (not always) larger than their diploid counterparts. In the 19th century, garden tall bearded irises were all diploids. Around 1900, plant collectors found tetraploid tall bearded species in the Middle East, and brought them into European and American gardens. The new plants attracted attention because of their taller stems and larger flower size. (There was no knowledge of chromosome numbers at the time, so iris growers and breeders were aware only of the difference in appearance of the new plants.)

The tetraploids were so popular with iris breeders that by the middle of the twentieth century, virtually all new TB varieties were tetraploid. This is still the case today.

One must be cautious, however, in associating tetraploids with large size. Size is determined by many factors. One of the very smallest bearded irises, the dwarf species Iris pumila, is a tetraploid although the blooms are only a few inches above the ground!

The great importance of tetraploidy in plant breeding is not that tetraploids are sometimes larger, but rather that more genetic combinations are possible with tetraploids than with diploids. With four copies of every gene instead of two, there are just many more possibilities!

One extraordinary aspect of tetraploid breeding is that hybrids between different species or types may be fertile if the parents are tetraploid, but sterile if the parents are diploids. The standard dwarf bearded irises (SDBs), for example, are fertile hybrids between tetraploid TBs and the tetraploid dwarf Iris pumila. So tetraploidy makes possible whole new types of fertile hybrids that simply could not exist otherwise. This is the main reason some hybridizers have taken such an interest in tetraploids.

'Bronze Beauty Van Tubrgen'

So now we come to the topic of this post: tetraploid arils. I love aril irises, with their exotic color patterns and dramatically shaped blooms. Most aril species are diploids. (I'm referring to pure arils here, not the arilbreds, which are a mix of aril and bearded ancestry.) In fact, the oncocyclus arils (the type that usually comes to mind when one thinks of arils) are all diploid. Crossing them with bearded irises, when it can be done at all, produces sterile hybrids.

Think of the possibilities that could open up if there were a family of tetraploid arils, like the family of tetraploid TBs!

Aril hybridizers have been thinking of that possibility for decades, and there are in fact some tetraploid arils, just not very many yet.

First, although all the oncocyclus species are diploids, there are two Regelia species that are natural tetraploids: Iris hoogiana and Iris stolonifera. A classic hybrid from these two species, 'Bronze Beauty Van Tubergen' (Van Tubergen, R. 2001) is also tetraploid. These are all lovely irises, but being Regelias, they do not have the oncocyclus characteristics, like huge globular blooms and big velvety black signals, that are the allure of aril irises for most people.

'Dunshanbe'

Second, a few arils with some oncocyclus ancestry are "accidental" tetraploids. Occasionally, a diploid parent produces a tetraploid seedling by chance. 'Persian Pansy' (Austin, 1960) and 'Tel Hashi' (Kellie, 1968) came about this way, but both seem to be lost now. 'Dunshanbe' (Wilkes, 1977), a seedling of 'Persian Pansy', is still being grown however, and is quite lovely with a dark sheen and nice veining. Its makeup is still more Regelia than oncocyclus, however.

Third, some breeders have created tetraploids deliberately using the chemical colchicine, that interferes with cell division, sometimes converting a diploid plant to a tetraploid. Usually, the plants created this way are unstable and sometimes unhealthy, but they can be crossed with other tetraploids to produce stable, reliable plants. 'Werckmeister's Beauty' (Werckmeister, 1992) came from this approach. In the 1980s, Sam Norris and John Holden created many tetraploid arils of predominantly oncocyclus makeup using this method. Alas, few have survived to the present day, and none are available commercially. Lawrence Ransom used one of these to produce 'Tadzhiki Eclipse' (Ransom, 1997) and 'Tadzhiki Bandit' (Ransom, 1997), both of which are still being grown in Europe and the US. 'Tadzhiki Eclipse' is, I think, the most oncocyclus-like tetraploid aril one is likely to be able to acquire today.

'Werckmeister's Beauty'

Through a little patience and diligence, I have acquired a small collection of tetraploid arils from the plant sale of the Aril Society International, occasional offerings of commercial growers, and the generosity of fellow aril hobbyists. I encourage others to do the same, especially those who live in the western US or other regions where pure arils can be grown without heroic measures being taken on their behalf. These are arils, not arilbreds, so they may need a little special attention regarding soil and siting. I have found them easier than most other pure arils, however.

If you are a hybridizer, you can cross them with each other to expand the family, or cross them with tetraploid bearded irises to create brand new types of fertile arilbreds.

Even if you are not a hybridizer, you can enjoy their bloom and know that you are helping preserve a very important group of plants, which may someday become the progenitors of new breeds of irises we can only imagine today.

If you can grow aril irises, have you tried any of the tetraploids? I think they are worth seeking out.

'Tadzhiki Bandit'

Arilbred Irises: A Touch of the Exotic

by Tom Waters

One of my favorite types of iris is hardly known to the general gardening public: arilbreds. These striking plants are deserving of much more attention.

What is an arilbred? The term aril applies to two groups of irises: the oncocyclus from the Middle East, and the Regelias from central Asia. (The word "aril" is a term for the prominent white color seen on the seeds of these types of iris.) These aril irises, although some of the most spectacular flowers in the genus Iris, often proved difficult to propagate and maintain in northern Europe or the US. Arilbred irises are the result of crossing these aril irises with the more familiar bearded irises. Many earlier breeders making these kinds of crosses were dreaming of flowers like those of the aril irises on plants that were as easy to grow as bearded irises. Today, this dream has largely become reality. Along the way, the endless gene combinations gave rise to a huge variety of flower types not even imagined before.

Seeds of an oncocyclus iris. Note the fleshy white collar or "aril", from which aril irises take their name.

Arilbred irises come in so many different colors, patterns, and forms that it is unwise to generalize about their appearance. Many, however, have large, globular blooms, a dark signal spot below the beard, and intricate veining.

'New Vision' (Tasco, 2012). Note the large dark signal and globular form. (Photo: Superstition Iris Gardens)

'Navajo Velvet' (McAllister, 2009).

'Oyez' (White, 1938). Note the intricate veining.

Arilbred irises grow extremely well in the western US and similar climates. They prefer conditions that are on the dry side during the heat of summer and the cold of winter, although they are not desert plants and will thrive on ample irrigation during the spring and autumn. In the desert southwest of the US, arilbreds often perform better than tall bearded irises, growing more rapidly and blooming more reliably. Growers in wetter climates, such as the eastern US, often find them more challenging to grow, although many are successful with them nonetheless. If you live in a wetter area, I recommend giving your arilbreds a particularly sunny spot with good air circulation and good drainage.

'Parable' (Johnson, 2011). (Photo: Mid-America Garden)

'Eyes on You' (Black, 2012). (Photo: Mid-America Garden)

'Refiner's Fire' (McGrath, 2007). (Photo: Pete McGrath)

'Aladdin's Gem' (Thoolen, 2002). One of the smallest arilbreds.

Arilbreds come in all sizes, from tall-bearded size to dwarfs only a few inches high. This is because all different types of bearded irises (tall, median, and dwarf) have been used to breed them, and also because the aril species themselves come in a wide range of sizes. Most arilbreds bloom earlier than the TBs, overlapping the standard dwarf bearded (SDB) and intermediate bearded (IB) bloom seasons. They do not have the branching and bud count seen on TBs: a single short branch and 3 to 4 buds is typical of many arilbreds. They make up for it with individual flowers that are showy and spectacular, and by often producing many stalks, even on a young clump.

Have you tried arilbred irises in your garden? How do they like your climate?