31 Ways to Build an Iris

Introduction

Although my interests are focused on the six tetraploid fertile families, I thought it would be interesting to enumerate all possible chromosome configurations of bearded and aril irises. There are 31 such configurations at the diploid, triploid, and tetraploid levels. The diagrams included here should help in picturing the relationship between the different types of irises and the expected result of crosses between different types. Those adept at three-dimensional visualization might want to picture the diagrams here stacked in space, with the tetraploid triangle topped by the triploid triangle topped by the diploid triangle to make a sort of truncated pyramid.

When a chromosome configuration is identified here as "fertile", "limited fertility", or "infertile", these are theoretical appraisals based on the number of chromosome sets that have similar sets to pair with. In practice, of course, a given plant may be more or less fertile than theory would suggest.

I've tried to list all known species with each type of chromosome configuration, and some examples of garden varieties as well. Comments, additions, and corrections are most welcome.

Diploids

chromosome configuration: diploid aril and bearded irises

There are six possible diploid configurations: AA, AP, AT, PP, PT, and TT. Many of the iris species found in nature are diploid.

 

AA

type: aril

expected fertility: fertile

plants in cultivation: some

These are the diploid arils, including all oncocyclus species and pure oncocyclus hybrids (OH), as well as the Regelia species, with the exception of Ii. hoogiana and stolonifera. This is a fertile family, although outcrossing to plants of other configuration is unlikely to produce fertile seedlings. Because I. korolkowii is the regelia most used in crossing with oncocycli, most RCs and OGs belong to this group. These are undoubtedly among the most beautiful of all irises. Unfortunately, they are also the most difficult to grow and propagate outside their native climate (mountains and deserts of the Middle East and central Asia). Hundreds of garden varieties have been produced since the late 1800s, but most are no longer in cultivation.

Species: all oncocyclus species, Ii. afghanica, darwasica, korolkowii, lineata.

Some garden varieties: Artemis, Babylonian Brass, Charon, Gamaliel's Wisdom, Heritage Orange, Judean Charmer, Kashmir Princess, Leo's Magic, Polished Brass, Purple Sequin, Shalah, Teucros, Tirat Tsvi.

 

AP

type: arilbred dwarf

expected fertility: infertile

plants in cultivation: none

This is the configuration one would expect to result from crossing diploid arils with I. attica or I. pseudopumila. Although it seems likely that someone would have tried such a cross at some point, there are no registered irises in this group. Any irises from such a cross would be expected to be infertile, barring a chance unreduced gamete.

 

AT

type: arilbred

expected fertility: infertile

plants in cultivation: few

This configuration results from crossing diploid arils with diploid TBs, MTBs, or 24-chromosome dwarf species such as I. suaveolens. Many of the first arilbreds fall in this category, including the famous 'William Mohr' and early varieties from C. G. White such as 'Oyez', 'Nelson of Hilly', and 'Myomy'. Most irises in this group are infertile or effectively so, and arilbred breeding in the first half of the 20th century was greatly frustrated by this fact. Few of these irises remain in cultivation today, having been superseded by the fertile amphidiploid arilbreds from C. G. White's later work. Lowell Baumunk's 'Hammurabi' is a modern example of this type.

 

PP

type: miniature dwarf bearded

expected fertility: fertile

plants in cultivation: few

This category is represented by two dwarf bearded species, Ii. attica and psedopumila. As far as I am aware, there are no registered hybrids between these species and only a couple clones have been named.

 

PT

type: dwarf or median bearded

expected fertility: infertile

plants in cultivation: none

This configuration would result from crossing I. attica or I. pseudopumila with an MTB, diploid TB, or one of the TT species. As far as I know, no plants of this sort have been registered and introduced into commerce.

 

TT

type: miniature tall bearded

expected fertility: fertile

plants in cultivation: many

This group includes most modern MTBs, as well as many antique TBs from the early 20th century and earlier. Recently, MTB breeders have been exploring the use of some of the lesser known TT species. This group is a fertile family but, being diploid, is unlikely to produce fertile offspring when outcrossed with irises of other groups.

Species: Ii. albertii, imbricata, pallida, perrieri, reichenbachii (some clones), scariosa, suaveolens, taochia, timofejewii, variegata.

Some garden varieties: Aachen Elf, Bangles, Bumblebee Delite, Chickee, Foursome, Kaleidescope, Mme. Chereau, Petite Monet, Quirk, Spring Thing, Welch's Reward, White Canary, Zebra, Zula

 

Triploids

chromosome configuration: triploid aril and bearded irises

There are ten possible chromosome configurations at the triploid level: AAA, AAP, AAT, APP, APT, ATT, PPP, PPT, PTT, and TTT. None of these constitute a fertile family, nor are any triploid species found in nature. These plants are thus all the result of wide crosses made by hybridizers.

 

AAA

type: aril

expected fertility: limited

plants in cultivation: few

Triploid arils are produced by crossing diploid arils with tetraploid arils. Some of the seedlings show some degree of fertility, and the use of triploid arils is one way to expand the fertile family of tetraploid arils. Most of these are RCs from I. stolonifera or I. hoogiana, although OGs are also represented in this group. As with all pure arils, gardenability is an issue.

Some garden varieties: Aaron's Shield, Clara, Garnet Tiara, Guinevere, Hera, Lucia, Midnight Journey, Persian Violet.

 

AAP

type: arilbred dwarf

expected fertility: limited

plants in cultivation: none

Plants with this configuration would result from crossing tetraploid arils with I. attica or I. pseudopumila. Crossing amphidiploid arilpums with diploid arils would also give this result. As far as I know, none have been produced by either method. They might be helpful in expanding the amphidiploid AAPP family with diverse aril genes.

 

AAT

type: arilbred

expected fertility: limited

plants in cultivation: some

Many arilbreds of this type have been produced by crossing amphidiploid arilbreds with diploid arils. This type of cross is usually made to introduce additional desirable aril characteristics into the arilbreds. Most of the OGB+ "three-quarter-breds" are of this type. This configuration would also result from crossing MTBs or diploid TB or TT species with tetraploid arils, although I am not aware of any having been produced in this way. Irises of this group sometimes have enough fertility to be bred back to either parental type.

Some garden varieties: Abu Zabad, Bib Black Bumblebee, Ech-Chams Harra, Emerald Fantasy, Izonya, Jeweled Veil, Jordanian Prince, Judean Rouge, Kasbah Queen, Mendocino, Nitzan, Petite Sirrah, Radiant Smile.

 

APP

type: arilbred dwarf

expected fertility: limited

plants in cultivation: few

Jonnye Rich produced three irises of this type by crossing I. pumila with diploid arils. The plants are MDB size and show some aril characteristics. It would also be possible to produce irises of this type by crossing I. attica or I. pseudopumila with amphidiploid arilpums.

The irises in this group are Pearls on Onyx, Tiny Pirate, and Tiny Tyke.

 

APT

type: arilbred dwarf

expected fertility: infertile

plants in cultivation: few

A number of arilbred dwarfs have been produced by crossing SDBs with diploid arils. In principle, the same configuration could be obtained by crossing an amphidiploid arilbred with I. attica / I. pseudopumila or by crossing an amphidiploid arilpum with a diploid MTB. These plants tend to be SDB sized, with some aril characteristics.

Some garden varieties: Calypso Clown, Canasta, Kelita Adah, Loudmouth, Omar's Eye, Plum Cute.

 

ATT

type: arilbred

expected fertility: limited

plants in cultivation: few

Irises of this type can result from diploid arils crossed with tetraploid tall beardeds or from amphidiploid arilbreds crossed with MTBs or other diploids. (The first type is more common.) Most of these were produced in the first half of the 20th century, and few are still in cultivation.

Some garden varieties: Blumohr, Etching, Miss Martha, Sigrid.

 

PPP

type: miniature dwarf bearded

expected fertility: limited

plants in cultivation: none

Irises of this type would result from crossing I. pumila with I. attica or I. pseudopumila. I do not believe there are any in cultivation.

 

PPT

type: miniature or standard dwarf bearded

expected fertility: limited

plants in cultivation: none

Plants of this configuration would be produced by crossing I. pumila with MTBs or other diploids, or by crossing SDBs with I. attica / I. pseudopumila. Nes's 'Cap Sounion' (1959) was produced from the latter type of cross. I do not believe any are in cultivation.

 

PTT

type: intermediate bearded

expected fertility: limited

plants in cultivation: few?

These are the result of SDB x MTB crosses, and could also be produced by crossing tetraploid TBs, BBs, or MTBs with I. attica / I. pseudopumila. I believe the first type of cross has been made by MTB breeders, but I do not know of registered varieties from such breeding. A few of the latter type have been registered over the decades or used in further breeding.

 

TTT

type: tall or miniature tall bearded

expected fertility: limited

plants in cultivation: few

Triploid TBs were produced in the early 20th century when tetraploid TBs became available and were bred with the existing diploids. More recently, some MTB breeders have crossed diploid MTBs with tetraploids from I. aphylla breeding. The former group is probably largely gone from gardens. Among the MTBs, it is often difficult to distinguish diploids, triploids, and tetraploids where the pedigree is complex.

Some possible MTB triploids: Ozark Dream, Ozark Maid

Some antique triploid TBs: Queen Caterina, San Gabriel, Frieda Mohr, Sunmist, Venus de Milo.

 

Tetraploids

chromosome configuration: tetraploid aril and bearded irises

There are fifteen possible chromosome configurations at the tetraploid level: AAAA, AAAP, AAAT, AAPP, AAPT, AATT, APPP, APPT, APTT, ATTT, PPPP, PPPT, PPTT, PTTT, and TTTT. These include six fertile families (the tetraploid arils, TBs, and I. pumila; and the amphidiploid SDBs, arilbreds, and arilpums). The nine remaining combinations are expected to have limited fertility, as they are unbalanced tetraploids with two sets that pair and two that do not.

 

AAAA

type: aril

expected fertility: fertile

plants in cultivation: few

For more on this group, see my Tetraploid Arils page.

 

AAAP

type: arilbred

expected fertility: limited

plants in cultivation: few

This is the configuration that results when an amphidiploid arilpum is crossed with a tetraploid aril. Elm Jensen has registered two such irises: 'Kazakhstan' and 'Moments Later', both from a stolonifera/pumila seedling as the arilpum parent.

 

AAAT

type: arilbred

expected fertility: limited

plants in cultivation: few

Irises of this type are produced when amphidiploid arilbreds are crossed with tetraploid arils. Earlier examples typically used I. hoogiana or I. stolonifera as the aril parent, and more recently Sharon McAllister has produced a number of irises of this type using tetraploid RCs. This group includes fewer irises than the triploid "3/4-breds" with diploids as the aril parent, and regelia characteristics are often prominent.

Some garden varieties: Armenian Descent, Bedouin Child, Celeste Azul, Code Talker, Inscrutable, Persian Art, Rebecca's Veil, Sky Signal, Urmia.

 

AAPP

type: arilbred dwarf

expected fertility: fertile

plants in cultivation: few

For more on this group, see my Arilpums page.

 

AAPT

type: arilbred median

expected fertility: limited

plants in cultivation: few

Plants of this configuration can be produced by crossing amphidiploid arilpums and arilbreds together, or by crossing tetraploid arils with SDBs. All known varieties are from the latter type of cross. Early breeders crossed garden dwarf bearded irises with regelia species; some more recent introductions make use of tetraploid RCs. The historic 'Zwanenburg' possibly belongs to this group, apparently the result of an unreduced gamete from its diploid aril parent, I. susiana.

Known garden varieties: Bakhshish, Benjamin, Black Dazzler, High Sierra Snow, Lilli-Hoog, New Era, Party Robe, Ray Serene, Spotless, Spring Caper, Vera-Anne, Vera-Beatrice, Vera-Louise, Vera-Marina, Vera-Olivia, Vera-Ruby.

 

AATT

type: arilbred

expected fertility: fertile

plants in cultivation: many

For more on this group, see my Amphidiploid Arilbreds page.

 

APPP

type: arilbred dwarf

expected fertility: limited

plants in cultivation: none

Plants of this sort would be obtained by crossing amphidiploid arilpums with I. pumila. Werckmeister's 'Nunatakr' and 'Plusia' (and possibly Miller's 'Bite Size' and 'Snuggles') are the only examples I know of.

 

APPT

type: arilbred dwarf or median

expected fertility: limited

plants in cultivation: few

Irises in this group result either from crossing I. pumila with an amphidiploid arilbred, or crossing an arilpum with an SDB ('Persian Sapphire' being the only one from this latter type of cross).

Known garden varieties: Baby Kabul, Bozrah, Persian Sapphire, Saletta, Wine Sundae.

 

APTT

type: arilbred median

expected fertility: limited

plants in cultivation: some

Most arilbred medians are the result of crossing SDBs with amphidiploid arilbreds. In principle, plants of this type could also be produced by crossing amphidiploid arilpums with TBs, although none of the latter are known to date. These irises are some of the most popular arilbreds of less than half aril content, and frequently win high awards in this category.

Some garden varieties: Byzantine Beauty, Cairo Love Song, Chain Reaction, Earfalas, Eye to Eye, Fairy Goblin, Jewel of Omar, Little Orchid Annie, Octave, Prairie Thunder, Prince of Egypt, Sajjetta, Suspect.

 

ATTT

type: arilbred

expected fertility: limited

plants in cultivation: some

These are the quarterbreds or "Mohr type" arilbreds from crossing amphidiploid arilbreds with TBs. These were popular in the mid-20th century, as they are easy-to-grow plants that show some aril characteristics. Interest in the group has declined somewhat, after improvements in the amphidiploid arilbreds made that group an often better choice for those interested in arilbreds. A number are still being produced, however, and many are attractive garden subjects.

Some garden varieties: Cope Goodwin, Coronation Tapestry, Desert Festival, Dune, Elmohr, Engraved, Gentle Poet, Hakuna Matata, Moonchild, Old-Fashioned Girl, Saffron Jewel, World Wide Web.

 

PPPP

type: miniature dwarf bearded

expected fertility: fertile

plants in cultivation: few

For more on this group, see my Iris pumila page.

 

PPPT

type: miniature dwarf bearded

expected fertility: limited

plants in cultivation: some

The classic cross for modern MDBs is SDB x pumila, which produces irises in this group (although there are smattering of pure pumila MDBs and many from SDB breeding as well). This group shows somewhat more fertility than one might expect, and breeding with other MDBs is not uncommon.

Some garden varieties: Alpine Lake, April Ballet, Azurea, Cradle Blue, Fuzzy, Gobo, Gold Canary, Little Rascal, Nuggets, Pixie Pirate, Robin's Egg, Saucy Sprite, Scruples, Secret Eye, Toyland.

 

PPTT

type: standard dwarf bearded

expected fertility: fertile

plants in cultivation: many

For more on this group, see my Amphidiploid Dwarf and Median page.

 

PTTT

type: intermediate bearded

expected fertility: limited

plants in cultivation: many

The classic cross for IBs, TB x SDB, produces irises of this type. A few have some fertility, but most breeding has focused on making making the TB x SDB cross with select parents. These are important garden plants, bridging the dwarf and tall bearded bloom seasons. The species I. albicans, presumably a natural hybrid of ancient origin, has this configuration as well.

Some garden varieties: April Fog, Attitude, Azure Echo, Broadway Baby, Confederate Soldier, Gaslight, Honey Glazed, Hot Fudge, Lemon Pop, Rare Edition, Shampoo, Silent Strings, Voila.

 

TTTT

type: tall bearded and border bearded

expected fertility: fertile

plants in cultivation: many

For more on this group, see my page on The 48-Chromosome Bearded Irises.

 

Some Thoughts

So what can be learned from an overview such as this? One simple observation is that some of these groups are much more developed than others. The reasons for this are many: available species, historical accident, gardenability, and popularity trends. It is unlikely that we will ever see hundreds of garden varieties of the PP diploid group (Ii. attica and pseudopumila), for example: There are not many different species to work with, and I. pumila is more varied and more useful in outcrossing to other types. In other cases, however, there would seem to be quite a lot of untapped potential for adventurous breeders to dip into.

A second observation is that development of the fertile families seems to drive the improvement of the garden irises. All our irises are either members of these families or rely on them for parental stock. The IBs could not have improved as much as they have over the decades, for example, were it not for improvements in the fertile families of SDBs and TBs. Modern OGB+ "3/4-breds" and arilbred medians would not exist as we know them if the fertile family of amphidiploid arilbreds had not reached a critical mass to allow ongoing improvement through breeding.

Triploids, although limited in their fertility, provide about the only way for the ordinary hybridizer to bring genes from diploid irises into the tetraploid fertile families. (The other option being to hope for an unreduced diploid gamete to appear by chance.) This is particularly important in the case of the arils, since all oncocyclus species are diploids. Unbalanced tetraploids are of less usefulness in expanding the gene pool, since their parental stock are members of the tetraploid fertile families already.

We can imagine a future when the genes from all the many delightful and beautiful species of aril and bearded irises are preserved in our garden plants, to be brought together in any imagined combination for long-term breeding projects. This future can be largely realized among the tetraploids, if the fertile families are sufficiently varied and inclusive. The PPPP family is self-contained and is not likely to expand in its gene pool. The TTTT family is expanding gradually, thanks to breeders working with I. aphylla and more recently other species in this group. Where the most work is needed, though, is in expanding the tetraploid arils with genes from the diploid oncocycli. This is probably the only way to keep the full genetic legacy of the oncocycli alive for the long-term breeding of garden irises.

 

 Tom Waters

September 2010

updated May 2015

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