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The Miniature Dwarfs:A Hybridizer's Survey of the Class, Its History, and Its Potential |
A Hybridizer's Survey
of the Class, Its History, and Its Potential
The miniature dwarf bearded irises (MDBs) are presently defined to
include all bearded irises less than 8 inches (20 cm) in height. This
simple definition says little about the great genetic diversity of
the dwarfs and their varied origins. The class encompasses three
major types with different chromosome configurations, more than any
other bearded iris class. This article is a survey of these different
types, what they contribute to the class, where they have come from,
and what their future may be.
The Miniature Dwarfs:
The genes of plants and animals are organized into chromosomes within the nucleus of each living cell, and these chromosomes come in groups called sets. The number and type of chromosome sets in an iris largely determines its fertility, and dictates what genes may be present for the hybridizer to work with.
Most bearded irises have chromosomes in sets of 12. Although there are differences from species to species, a set of 12 from one species is more or less compatible with a set of 12 from another species, making it possible to combine genes from different species in any desired combination. I will use the symbol T to represent a set of twelve chromosomes. You can think of "T" as standing for "twelve", or for "tall bearded" (TB), the most popular type of bearded iris whose chromosomes come in sets of twelve.
There are also bearded irises, all of them dwarfs, whose chromosomes come in sets of 8. Iris pumila is the most important member of this group, so I will use P to represent a set of 8 chromosomes.
With only the rarest exceptions, dwarf bearded irises are tetraploid, meaning they have four sets of chromosomes. There are five possible arrangements of P and T chromosome sets in tetraploid bearded irises: PPPP, PPPT, PPTT, PTTT, and TTTT. Only the first three configurations occur in hybrid MDBs, and they will be the focus of this review.
Irises with two sets of each type, PPTT, are called amphidiploids. They are generally fully fertile, with a chromosome count of 8+8+12+12, or 40. The best-known irises of this type today are the standard dwarf bearded (SDB), which were first produced in the early 1950s from crosses between TBs (TTTT) and the miniature species I. pumila (PPPP). Irises of this type have always been a part of the MDB class, and its predecessor DB class before the modern classification system was established in 1958.
I. lutescens is a dwarf species from the western Mediterranean: Spain, France, Switzerland, and northern Italy. It has many synonyms, including I. chamaeiris, I. italica, and I. olbiensis. Its natural height spans both the MDB and SDB classes as currently defined. It is almost never branched, bearing one or two buds in a single terminal. It ranges in color from blue, violet, and purple, to yellow, cream, and off-white, with some blends and bitones. For many years, the dwarf bearded irises of gardens in western Europe and North America were selected forms of I. lutescens, along with some natural hybrids of I. lutescens with other species. It was thus the prototypical "dwarf iris" until the middle of the 20th century.
Its chromosome configuration is thought to reflect its origins as a natural hybrid between a T-type iris and a P-type iris, perhaps I. pallida and I. pseudopumila. Some well-known examples are historic dwarf irises such as 'Bride' (Caparne, 1901), 'Path of Gold' (Hodson, 1943), and 'Black Baby' (Sass, 1955). Note that early registrations did not include height information, so not all I. lutescens cultivars, registered as dwarf bearded (DB), would necessarily meet the requirements of the MDB class. A number would be considered SDBs today, and a few even intermediate bearded (IBs). Work with this type of iris ended rather abruptly in the 1950s, when they were essentially supplanted by the new SDBs from TBs crossed with I. pumila.
A new era of dwarf and median breeding was ushered in in 1951, when Paul Cook introduced the first TB/pumila hybrids, dubbed "lilliputs". These new irises were in the same height range as the type Ia dwarfs, although tending toward the taller end of the range, and often bearing a branch with a single bud. They greatly extended the range of available colors and patterns, bringing in all the variety of the TBs of the time, as well as the extraordinary diversity from I. pumila, including its varied and often dramatic "spot pattern". From the beginning, dwarf iris connoisseurs have had an ambivalent relationship with the SDBs. Were they dwarfs (because of being similar in height to the type Ia dwarfs), or intermediates (because they came from crossing a dwarf with a TB, and could be branched)? There was much consternation and several false starts in resolving this issue, which culminated in the 1958 classification. The new classification created two classes, MDB, and SDB, with a dividing line of 10 inches (subsequently lowered to 8 inches, where it remains today). Most of the TB/pumila hybrids are SDBs, but some are small enough to be classified as MDBs.
These irises have the same chromosome configuration as the type Ia dwarfs, and are perfectly fertile with them. Although some such crosses were made early on, breeders quickly abandoned the type Ia dwarfs in breeding, preferring to cross the more colorful Ib types amongst themselves instead. As time has gone on, the SDB class has become even more varied and developed, with ruffling, wide petals, and an enormous range of color patterns otherwise unheard of in the dwarfs, such as tangerine pink, bicolors, and plicatas in all their variety. MDBs coming out of pure SDB breeding have become increasingly common, and now represent a large majority of new introductions in the class each year. Recent award winning MDBs are almost all of this type, with familiar examples being 'Chemistry' (Black, 2003), 'Icon' (Keppel, 2008), and 'Keeno' (Johnson, 2009).
Despite their obvious value in giving us polished, modern-looking MDBs in an outstanding range of colors, they do come with a downside. Because the normal height distribution for plants of this type is centered in the SDB range, many MDBs produced this way "just barely" fall below the height limit, and can be indistinguishable in the garden from the smaller SDBs. The MDB class thus faces problems familiar from the border bearded class: too many cultivars pushing the upper height limit, prone to growing out of class, and lacking distinctiveness to separate them from their larger kin.
The inventive hybridizer Ben Hager sought a way to retain the advantages of the type Ib dwarfs while mitigating their tendency to seem too large and coarse for the class. His solution was to repeat the TB/pumila crosses that produced this group, but rather than using the large TBs, he would shift to the daintier tetraploid miniature tall bearded (MTBs) from I. aphylla breeding. The resulting seedlings would be fully fertile with SDBs and type I MDBs. This is a good idea, and indeed gave him some of what he was looking for. His award-winning 'Libation' (Hager, 1975) and 'Gizmo' (Hager, 1977) indeed preserve the delicacy and charm desired in MDBs. Alas, this project was not taken up by others.
These are miniature dwarfs with three P sets and one T set, which is the usual result of crossing an amphidiploid (SDB or type I MDB) (PPTT) with I. pumila (PPPP). Their chromosome configuration is written PPPT, and the total chromosome number is 8+8+8+12=36. Some of these predate the practice of hybridizing, being natural hybrids cherished in gardens alongside the type Ia I. lutescens dwarfs. The best known, and best loved, is 'Atroviolacea' (Todaro, 1856), presumed to be a hybrid between I. lutescens and I. pumila. The three P sets ensure small size and daintiness, serving to reduce the sometimes overly large type I dwarfs. The drawback of this chromosome configuration is that it is unbalanced, limiting fertility and making long-term hybridizing projects frustrating.
These are hybrids in which the amphidiploid parent is an I. lutescens cultivar. A number of these were produced in the 1950s, after I. pumila was first introduced into American gardens and hybridizers began crossing it with the existing type Ia dwarfs. 'Primus' (Welch, 1950) is an example. These ceased to be produced when the TB/pumila SDBs supplanted I. lutescens in dwarf breeding.
Here the amphidiploid parent is an SDB (or, rarely, a type Ib MDB). From the mid-1950s through the 1980s, this was thought to be the most satisfactory cross for MDBs, with the SDB parent providing color variety and polished form, and the pumila parent lending daintiness, earliness, and floriferousness. Although some of these hybrids showed some fertility, others were infertile or just difficult to hybridize with. This hampered reproducing the full range of SDB colors and patterns in MDBs of this type. Nevertheless, they remained popular garden plants until the end of the 20th century, when they took a back seat to the type Ib dwarfs from pure SDB breeding. Some well-known examples of type IIb MDBs include 'Sky Caper' (Warburton, 1963), 'Zipper' (Sindt, 1979), and 'Alpine Lake' (Willott, 1981).
I. pumila has already been mentioned repeatedly in this article, as being the source of the SDBs and the type Ib MDBs, and then of the type IIb MDBs from backcrossing SDBs to I. pumila. It is also behind the modern IB class, which resulted from backcrossing SDBs to TBs. I. pumila is a truly diminutive dwarf, never branched, and with a stem so short that the ovary appears to sit atop the rhizome, with flowers held aloft by the long perianth tube. Most are only 3 to 6 inches in height. It grows wild from Austria and the Czech Republic, through Rumania and Ukraine, and over the Caucasus into Armenia and northeastern Turkey. The color range spans blue, violet, purple, cream, yellow, white, brown, reddish, and grayish. It is noted for its highly variable "spot pattern" on the falls which can be dark violet, brown, red, olive, or purple, and varies from a bold spot with a narrow outline of ground color, to a soft patch of color, a set of rays, or a half-moon halo around the beard.
I. pumila is a tetraploid, PPPP, with a total chromosome count of 8+8+8+8=32. It is thought to have originated as a natural hybrid between two similar diploid species, I. attica and I. pseudopumila.
I. pumila grows in inland continental areas, often at some elevation. Thus it is quite winter hardy, and valuable in breeding dwarfs for cold-winter climates. Conversely, it can be unhappy in the mild-winter climates of the American South or coastal California. It requires a definite winter chilling to bloom and thrive.
Although its lasting legacy for garden irises is no doubt the SDB class and their MDB and IB offshoots, I. pumila is a desirable garden plant in its own right, and a number of selected cultivars have been introduced. For a time, it rivaled the type I and type II MDBs as a source of new cultivars. Its potential is far from exhausted, especially as only a handful of cultivars, mostly from the western part of its range, were used in early breeding in the 1950s and 1960s. Four I. pumila cultivars have received the Caparne-Welch medal: 'April Morn' (Welch, 1952), 'Atomic Blue' (Welch, 1961), 'Sun Sparkle' (Sindt, 1968), and 'Little Drummer Boy' (Willott, 1997).
Note that today, I. pumila selections may be registered in the SPEC class, as well as the MDB class.
The history of dwarf iris breeding falls naturally into three phases. In the early phase (pre-1950), it was dominated by type Ia dwarfs, I. lutescens and its cultivars, and a smattering of hybrids. The introduction of I. pumila ushered in the middle phase (about 1950 to 1980), which displays the greatest variety of genetic types and the most adventurous hybridizing. Type I, II, and III MDBs were all prevalent in gardens, each offering something the other types lacked. The center of gravity at this time was the type IIb dwarfs, from SDB/pumila crosses, which I think of as the "classic" MDB recipe. The late phase (post-1980) is increasingly dominated by short selections from pure SDB breeding (type Ib), with all their riotous colors and patterns, but often at the expense of delicacy and early bloom.
I've compiled a list of Caparne-Welch Medal winners (Caparne Award prior to 1983), color coded according to the types described in this article. I've sorted them by registration year, rather than award year, to make it easier to see chronological trends in breeding. When something is classified as type I or type II, without an "a" or "b" subtype, it usually means both I. lutescens and modern SDBs were involved.
Award Year Cultivar Registration Year Type 1952 Atroviolacea 1856 IIa 1950 Sound Money 1934 Ia 1957 Path of Gold 1941 Ia 1953 Beauty Spot 1947 IV 1951 Primus 1950 IIa 1954 April Morn 1952 III 1955 Blazon 1952 Ia 1966 Promise 1952 V 1956 Sparkling Eyes 1953 II 1958 Veri-Gay 1953 II 1960 Cherry Spot 1954 II 1962 Black Baby 1955 Ia 1959 Blue Frost 1956 1964 Fashion Lady 1956 I 1961 Angel Eyes 1958 II 1963 Bee Wings 1959 IIb 1967 Knick-Knack 1959 Ib 1965 Atomic Blue 1960 III 1978 Orchid Flair 1960 IIb 1968 Sky Caper 1962 IIb 1969 Irish Doll 1962 I 1970 Bumble Wings 1962 1975 Lemon Puff 1964 Ib 1971 Blue Beret 1966 IIa 1972 Sun Sparkle 1967 III 1973 Buttercup Charm 1969 Ib 1974 Three Cherries 1971 Ib 1976 Curio 1971 Ib 1977 Tom Thumb 1972 Ib 1979 Libation 1974 Ic 1980 Nuggets 1975 IIb 1981 Penny Candy 1976 Ib 1982 Garnet Elf 1976 Ib 1987 Gizmo 1976 Ic 1985 Zipper 1978 IIb 1989 Alpine Lake 1980 IIb 1988 Ditto 1981 Ib 1990 Pussy Toes 1981 IIb 1991 Puppet Baby 1981 Ib 1993 Sparky 1983 Ib 1992 Chubby Cherb 1985 Ib 1994 Funny Face 1986 1998 Snuggles 1987 IV 1995 Spot of Tea 1988 Ib 1997 Grapelet 1989 Ib 2002 Scruples 1989 IIb 1996 Cinnamon Apples 1990 Ib 1999 Tooth Fairy 1992 Ib 2000 Bugsy 1992 Ic 2001 Hey There 1992 Ib 2003 Squiggles 1994 Ib 2005 Little Drummer Boy 1997 III 2008 Yak Attack 1997 Ib 2004 Dinky Circus 1998 Ib 2006 African Wine 1998 Ib 2007 Wise 2000 Ib 2009 Tiny Titan 2002 Ib 2010 Chemistry 2002 Ib 2011 Fission Chips 2003 Ib 2012 Dollop of Cream 2006 Ib 2013 Trimmed Velvet 2006 Ib 2014 Icon 2007 Ib 2016 Gecko Echo 2008 Ib 2018 Kayla's Song 2008 IIb 2015 Keeno 2009 Ib 2017 Cute as a Button 2009 Ib
Another graphic which tells a similar story was pulled together by using the AIS iris wiki to capture dwarfs registered in each decade year (1930, 1940, 1950, etc.). I was not particularly careful to make sure my lists were exhaustive or my type assignments perfect, but I think the overall pattern of how the popular types have changed over time is clear enough. It's also clear that dwarf breeding had its greatest heyday around 1960. It would be wonderful if a similar level of activity and innovation could be regained today and in the years ahead.
Although these three types (and their associated subtypes) constitute nearly all the MDBs that have been produced, they do not exhaust all the possibilities. Here are a few other types of breeding that have given (or might give) MDBs.
Aril species and hybrids have been crossed with dwarfs to produce MDB-sized plants. In recent decades, these are usually assigned to an appropriate arilbred class. Early on, however, some breeders placed them in the DB or MDB class, and this remains an option if the hybridizer feels they fit that class better, due to lack of strong aril characteristics, for example. 'Beauty Spot' (Marx, 1947) and 'Snuggles' (Miller, 1988) are Caparne-Welch winners from aril breeding.
The psammiris group of irises, including I. humilis (also known as I. arenaria and I. flavissima) and I. bloudowii, rather distant relations of other bearded irises, grow in sandy soils in Asia, with an outpost in eastern Europe. Early dwarf breeders were fascinated by them, and crossed them with type Ia dwarfs. Chromosome configuration made them almost completely sterile, but some of the initial hybrids were quite charming. 'Promise' (Cook, 1952) was the only Caparne-Welch winner of this type. Presumably psammirises could be crossed with SDBs with similar or superior results. Today, these would most likely be registered as SPX.
(48 chromosomes) There are some TTTT tetraploid species that might meet the criteria of the MDB class, particularly if hybridized and/or selected for small size. I. reichenbachii is considered a dwarf species, and exists in a tetraploid form. Although it is unbranched and delicate, its height in most forms pushes the boundary of the class. There are also very small forms of I. aphylla and I. schachtii that might fall into the MDB range. Jim and Vicki Craig produced two tetraploids from their aphylla-based MTB lines that were registered as SDBs.
(24 chromosomes) The dwarf species I. suaveolens (formerly often called I. mellita) is comparable in size to I. pumila, and there are also small diploid forms of I. reichenbachii that could be crossed with it, perhaps leading to interesting hybrids. 'Buddha Song' (Dunbar, 1970) is a hybrid of the diploid TB 'Rhages' with I. suaveolens, registered as an MDB at 7 inches. Sean Zera is developing a line of hybrids from I. suaveolens and diploid TB I. pallida with an eye to producing MDB-sized plants.
(16 chromosomes) There are two diploid species with P chromosome sets, I. attica from Greece and I. pseudopumila from Italy. Presumably diploid MDBs could be selected from these species or from hybrids between them.
January 2019
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Unless otherwise noted, all text and illustrations copyright Tom Waters and all photographs copyright Tom or Karen Waters. Please do not reproduce without permission.