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Development Of the Miniature Dwarf Bearded Irises (under Construction)

From Chapter 8 of "The World of Irises" by Barbara B. Whitehouse and Bee Warburton © 1978 AIS

Miniature Dwarf Beardeds

Barbara Whitehouse and Bee Warburton

While the sight of the first crocus may signify the return of spring to most people, it is the sight of the first miniature dwarf bearded iris that spells "spring" to irisarians. The first of the bearded irises to bloom, miniature dwarfs herald the season anticipated so eagerly during the long winter; each iris lover should grow at least one or two clumps of them for that reason alone. However, they are so charming that one or two clumps may ultimately become a whole bed or border.

By definition, miniature dwarfs are less than 21 cm (8 inches) tall and have an unbranched stalk. While there are no defined limits to flower size, a bloom should be no larger than 5-7.5 cm (2-3 inches) across in order to be in proportion for the height and the dainty foilage. Many inherit from the species a tendency to produce a multiplicity of stalks that make up for the lack of branching and produce a solid sheet of bloom.

CULTURE

Miniature dwarf bearded irises are small and dainty, useful as edging plants in a mixed perennial border or in front of taller and later irises. They are charming planted in a miniature dooryard garden where, protected and warmed by reflected sunlight, they will bloom even earlier. They are most at home in a rock garden where the rough stones emphasize their daintiness and enhance the vertical lines of the foliage when bloom season is over. However, they must be protected from encroaching mats of fast-spreading rock garden favorites.

While seemingly delicate, miniature dwarfs are extremely hardy. Even in bloom, they are relatively undamaged by light frost, although it is wise to protect plants from severe frost when possible. Their cultural requirements are those of all bearded irises, but because they have shallow root systems, heaving during freeze/thaw conditions can be more of a problem than it is for their larger relatives. It is wise to cover the plants with a light-weight mulch once the ground has frozen. Late-planted rhizomes which have had little time to develop root systems can be further protected from heaving by putting a brick or rock directly on the rhizome for the winter.

The pure pumilas are small and shallow-rooted plants, requiring some care to maintain. They demand a long winter dormancy, and are easily smothered by neighboring plants, and easily uprooted by winter heaving. To keep individual clones, of which several hundred have been numbered or registered (MIS 1970), it is necessary to transplant often. The variability that makes them such treasures indicates that in their native places they increase by seeding; indeed, growing them from seed is the surest way to maintain them. They are well worth the effort, especially as rock garden plants.

Other miniature dwarfs including chamaeiris-pumila and lilliput-pumila hybrids, perform well throughout the temperate zone. They seem to be less bothered by most iris pests and diseases than are their larger relatives. Leaf spot can be disfiguring; other kinds of plants between clumps serve as buffer zones to prevent the disease from spreading readily. Borers, less likely to attack these small plants, emerge in the north when the species pumilas are in bloom. Start your spray program for your entire iris planting before then, if possible, and spray again as soon as their bloom has ended. Since miniature dwarf foliage is only about 15 cm (6 inches) tall, the newly hatched borer has only a short way to go before reaching the rhizome-and the rhizomes are so small that a hungry borer can consume several before you realize it. Any spray program against borers (chap. 24) should also help prevent infestations of aphids and protect newly formed pods from damage by verbena bud moth.

HISTORY

Most of the history of the early dwarf irises from their origins mainly among the species of Italy and France are well documented in the manuscript put together by the Wrights at Cornell in the 1920s and finally published 50 years later as one of the Historical Chronicles-the Dwarf Bearded Irises, no. 26, consisting of reprints of articles from botanical journals of years 1800-1930. Though there is some record of smaller dwarf types, the great majority of dwarf irises produced and grown then and through the 1940s were of what came to be known as the "chamaeiris complex," though derived mostly from I. olbiensis and I. italica, related but larger and lustier species than I. chamaeiris itself. Since the time of Linnaeus these irises have often been incorrectly called I. pumila, or "pumila dwarfs," which has made difficult the interpretation of early crosses involving these species. H. P. Sass once expressed the opinion that hybrids of pumila imported and used by him were in fact chamaeiris varieties. Chromosome counts and cytogenetic studies later confirmed this, and also demonstrated that some of the smaller dwarfs, more prized individually and supposed to be pure I. pumila species, were natural hybrids of I. pumila with some of the larger "charnaeiris" dwarfs.

'Atroviolacea', the most famous of these, listed by Todaro in 1856, is often called the "cemetery iris" because it was carried by our ancestors across the country and often used to cover graves. 'Azurea' and 'Coerulea', nearly as famed, were discovered in the wild and have been cultivated in gardens since 1880; one of them is pictured in Dykes's (1913) I. pumila plate. These three are true miniatures, but for the first half of the twentieth century few such small dwarfs were available to gardeners.

THE CHAMAEIRIS DWARFS

The larger types, purple, gray blue, yellow or white, were grown everywhere. They were bred by Goos and Koenemann ( 'Citrea', 'Florida', 'Schneekuppe') and Junge ( 'Die Fee') in Germany, and Capame ( 'Bouquet, Cyanea, 'Sapphire') in Britain. Van Tubergen listed 'Fairy' in 1912, and in 1914 Millet, in France, introduced 'Marocain' and 'Negus'. In the 1920s another French breeder, Andre, introduced 'Lt. de Chavagnac' and 'Jean Siret', known for their dependable rebloom. During that decade, Burchfield, the foremost American dwarf iris breeder, created many outstanding varieties.

The gold-orange iris, 'Burchfield', registered posthumously by the American Iris Society, is one of his best. The pre-World War II years were highlighted by the Sass introductions, Sass 'Little Jewel', Sass 'Rose Mist and 'Tony', and the chamaeiris dwarfs were further improved during the war and postwar years by Hillson ( 'Tiny Tony'), Hodson ( 'Path Of Gold') and Marx ( 'Blue Mascot'). Production continued into the 1940s and early 1950s with the Welch introductions, the bright red-purple 'Blazon' and petunia purple 'Stylish', white and yellow 'Whitone', and golden yellow 'Orange Glint'. One of the last of the chamaeiris complex to be introduced, and one of the best in quality and as a parent, the Sass 'Black Baby', was released in 1955.

OTHER HYBRIDS

The Mediterranean spcies or subspecies that were the forbears of all these larger dwarfs were limited in color and pattern range. Somewhat bitoned but seldom of striking contrast, they lacked the sparkling clarity of color for which plant breeders strive. This limitation inspired some breeding with other dwarf species. I. arenaria and I. flavissima. These two small species are now recognized as synonymous and both are included as forms of I. humilis Georgii (chap. 1). Because they are so familiar under their synonyms, irisarians will undoubtedly continue to speak of them as "the arenaria complex". They are dainty plants some 15-20 cm (6-8 inches) tall with saucy bright gold flowers, fleeting of bloom.

Crosses with the chamaeiris complex were most successful, with distinctive new forms and colors produced by blending of their bright yellow with the anthocyanin coloring of the chamaeirises, but they were almost entirely sterile. The earliest of these included 'Ylo' from I. chamaeiris x I. arenaria; 'Jenny', from I. flavissima x 'Coerulea'; and 'Valery Germanis', from I. flavissima x 'Hungarica', one of several such hybrids produced by Karl Ugrinsky (chap. 11). Others were Hillson's 'Bronya', 'Cream Tart', 'Mist O' Pink', and 'Tiny Treasure', Cook's 'Keepsake' and 'Tampa', and the lovely 'Promise' from a cross of (chamaeiris) 'Balkana' with I. bloudowii , another member of Ugrinsky's Psammiris group. Welch's 'Cup and Saucer', and Zickler's 'Buster Brown' are notable examples of this personable group. There is no reason to suppose that the arenarias would not form even better hybrids with the pumila-talls, if this were given a trial, but all would undoubtedly prove equally sterile, as are the dainty 'Pumar Alpha' and 'Pumar Beta', produced by Ackerman from the wide and difficult cross of I. pumila x I. arenaria .

I. mellita is a diploid also, and hence gives mostly infertile seedlings in dwarf crosses; the mellita hybrids proved less successful in other ways. I. mellita itself, though with wildflower charm, has wide flat standards and narrow downhanging falls, and its coloring in the yellow forms is rather of a straw tint, while those with anthocyanin coloring are of a dull brown red. Its foliage is falcate (sickle-shaped) which in hybrids has an untidy appearance, and its overlarge spathes seem to predominate. Moreover, like all members of this Balkan complex- I. reichenbachii, I. balkana, I. bosniaca-it passes on to its hybrids susceptibility to the ugly anthocyanin streaking of virus infection; because of their greatly reduced fertility this cannot easily be bred out. On the other hand, it passes down some of its charm to its hybrids, the best, like 'Lavender Dawn', showing a crisp, clear, almost transparent lavender-orchid coloring.

All of these plants have a limited inheritance, and none could offer any competition to the marvelous diversity of Iris pumila, which revolutionized the breeding of the small bearded irises. The collections of species sent to America by friends in Europe, and sought out in Europe, the Near East, Russia, and India by the Randolphs (1959, 1961), became available to hybridizers in the late 1950s. Many dedicated workers experimented with this bonanza of new plant material, but it was the first dwarf irises from I. pumila, so small, so clearcut and so exquisite in their color combinations, that inspired the very particular devotion that led to the founding of the Dwarf Iris Society and later of the Median Iris Society, and to the worldwide dissemination of plants and information.

IRIS PUMILA L.

Iris pumila demonstrates all three of the themes pointed out by Lenz in his introduction to chapter 1. It is the product of hybridization between related groups of newly formed species (Randolph and Mitra 1959); it is tetraploid, and it carries an array of colors and patterns not surpassed by any other Iris group. This little iris, seldom more than 15 cm (6 inches) tall with flowers but 5 cm (2 inches) across, is known in "blue, dark and light blue, lavender blue, light and dark violet, reddish violet, sulfur yellow, lemon yellow, light yellow" (MIS, 1970). These colorings may be uniform, but usually show contrasting patches commonly referred to as "spot pattern" in their falls. Such patterns range from a few lines below the beards, to narrow crescents or halos, to half spots or full spots with narrow edging of the standard color. Full bushy beards in white, matching blue or purple, or occasionally yellow, accent the blades of the falls, but are yellow, orange or brown within the hafts. The falls commonly tum under, but sometimes flare, a trait that can be selected by the hybridizer. The flowers are stemless, or nearly so, except for rare Russian forms. Their long perianth tubes, from 5 cm to as much as 15 cm (2-6 inches), are sheathed in tight-clasping spathes and basal leaves, and they often produce more than one of their tiny scapes from each rhizome, so that each clump is capable of making a solid sheet of brilliant color.

Iris pumila is also the most fragrant and the most variable in fragrance of all iris groups, smelling, as Prodan says, like vanilla, lemon, heliotrope, wild orchids, violets, or the sweet-spicy scent of that singular contribution by the genus Iris to the world's loveliest fragrances, the orrisroot.

Pumila foliage is a pleasing dark green, and is variable in size, approximately 10-18 cm (4-7 inches) in length and 8-18 mm (1/3 to 5/8 inches) in width; it tends to overtop the flowers and lengthen after blooming. It is completely deciduous and separates cleanly from plants in the spring cleanup.

PUMILAS IN THE NEW WORLD

Since its arrival and distribution in America, I. pumila has been the foundation for three essentially new groups of garden irises in sizes adaptable to our changing gardens; our new miniature dwarf dass as well as the standard dwarfs (chap. 9) and the intermediates (chap. 10) all owe their existence to this sparkling midget, whose marvelous combining ability, well displayed in these three bearded iris classes, awaited the evolvement of the superlative modem tall beardeds. I. pumila has not proved persistent in gardens. Though it was brought to England in the nineteenth century by soldiers returning from the Crimea, it was never widely distributed there and was almost unobtainable in America until the 1940s, when it became available through the persistence of Robert Schreiner and Paul Cook. In the 1930s, Schreiner had imported seed from three sources-from the Crimea, from the University of Cluj in Romania, and from Vienna (Davidson 1965). The variety 'Nana' was named from the Crimean seed, and 'Carpathia' and 'Sulina' from the Romanian seed. None were named from the Austrian seed, but selections sent to Paul Cook and selectively bred by him resulted in varieties nearer than any previous offerings to real blue. Two of them he named 'Remnant 'and 'Sky Patch'.

The original Schreiner selections have proved to be some of the best pumilas tested for combining ability. 'Nana' gave good red coloring to its seedlings, 'Carpathia' was a breeder for form, and 'Sulina' was one parent of the famous sibs, 'April Morn' and Welch H-503, the latter especially a superlative breeder for the wide rounded form favored by modern judges. Some of the Russian pumilas, more slender of form with more restrained foliage, proved also to be superior, but many of the Russian forms have not been tested for breeding. Of these forms sometimes recognized as species, I. aequiloba was never widely distributed in America, but I. taurica , which Rodionenko calls "the pumila from the Caucasus," shows no noticeable difference from other forms of I. pumila in crosses with tall beardeds or with other pumilas, nor does the taurica-pumila hybrid, 'Tiny Taurus'. I. alexeenkoi , according to Rodionenko (1967), is a dark purple form of I. pumila with larger plants and flowers, but the form in distribution in America is no darker than many pumilas, and not nearly as large as some.

PUMILA HYBRIDS

Both the chamaeirises and the pumila-talls were tested with pumila forms; both types of crosses were successful, but it soon became clear that the best of the new miniatures were those that carried the recombined genes of the new tetraploid tall bearded through a Cook seedling from San Francisco x pumila, the first known lilliput to be used in breeding. 'Sparkling Eyes' and 'Cherry Spot' were the best of these, and remain as favorite white miniatures with strongly contrasting fall patches. I. pumila proved to be a superlative breeders' iris, and its ability to transfer genes from the well-developed new tetraploid tall beardeds to the smaller bearded irises was its great contribution to the development of modern bearded irises.

In this respect, a dainty small rose-purple form of I. pumila that was supposedly collected on the island of Crete, proved to be unique in combining with the plicata pattern of the tall beardeds to produce first-generation plicata lilliputs. This popular little species was commonly dubbed 'Cretica', and later registered under this name. Because of its unusual southern origin, Cretica itself and to some extent its progeny have proved adaptable to southerly gardens where other forms of the species have failed to thrive.

Oddly enough, some of the desired lilliput patterns, their diverse plicatas and the tangerine pinks, have not been reproduced in the 36-chromosome miniature dwarfs, probably because their low level of fertility prevents the necessary gene recombinations. However, the lilliputs themselves in advanced generations segregate just enough to produce shorter plants, and it is possible to breed them for small size with undiminished vigor and fertility. Before the dividing line between miniature and standard dwarfs was changed from 25 cm (10 inches) to 21 cm (8 inches), many of the small Lilliput segregates had been registered in the miniature dwarf class. Actually, the dividing line is not only one of size and season, but even more of horticultural or even botanical qualities. The greatest care is needed to preserve the essential daintiness of the miniature, which is not a function of the distance between the soil surface and the top of the flower.

CHROMOSOME MYSTERIES UNVEILED

The chromosome composition of I. pumila explains its success story. Karyotype studies of I. pumila by J. Mitra (1956) and Randolph and Mitra (1959) show that it is a tetraploid hybrid with four sets of 8 chromosomes. Two sets are like those of I. pseudopumila and the other two like those of I. attica . Both of these related small species show diversity of form, and particularly the diversity of color that results from their having both anthocyanin and plastid yellow pigments, which is the sign of recent speciation. Both are diploid species, with 16 chromosomes in two sets of 8. It seems probable that having diverged from a common ancestor and become separate species, they met and hybridized as diploids, then doubled to become the tetraploid I. pumila, most successful of all small bearded species. Discovery of forms of I. pseudopumila known previously only from Italy and Sicily, not far from the known habitat of I. attica in Jugoslavia suggested the eastern Adriatic as their probable meeting place. Here I. pseudopumila is smaller and daintier than in its Italian form, and is nearly stemless in contrast to the 15-20 cm (6-8 inch) stem of the Sicilian form. Tiny and stemless everywhere, I. attica in its Jugoslavian form has been at times classed as a subspecies of I. pumila, and it varies enough from the Greek forms to have been published as a separate species-I. ochridana Hayek (=I. pumila ssp. attica Boiss & Heldr.).

Whatever the source of its ancestors, I. pumila, a well-endowed child of nature, started forth on its expansion north, then east and west with all the inheritance needed for adaptation to new habitats. From its point of origin near the Adriatic coast, it established itself from Czechoslovakia and Austria across the Balkans and into Russia as far as the Ural Mountains.

In Russia and the Balkans (MIS 1970), I. pumila has differentiated until it has become a problem for taxonomists, subject to the usual lumping and splitting. Rodionenko (1967) considers all to be variants of the one species, but others have named many forms as species. In nature, pumila variants have intercrossed with other species in the past, and are still forming hybrids where they grow.

====================================================================================================== Figure 2. Idiogram of the gametic chromosomes of I. pumila (2n=32), showing its postulated origin from the diploids, I. attica and I. pseudopumila (2n=16). Both figure 2 and figure 3 illustrate the origin of tetraploids by hybridization and doubling of chromosomes of diploids. Garden Irises.
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====================================================================================================== near other compatible species, although their habitats are diminishing. In the Turda Gorge, south of Cluj in Romania, they have grown alongside I. aphylla , also a tetraploid but with 48 chromosomes, and the two have formed natural hybrids to which botanists have given species names. I. binata is supposed to be such a 40-chromosome hybrid, although perhaps unknown in American collections since all counted by Yendall (1970) proved to be hybrids of 36 chromosomes as is I. barthii, apparently from the backcross to a 32-chromosome parent.

In its dispersal, I. pumila diversified further not only in its physical characters, but also in its chromosomes. Karyotype studies show that the chromosomes of the Russian I. taurica differ somewhat from those of the more intensively studied Austrian forms of I. pumila , and that the Crimean 'Nana' and other Russian clones have a reduced complement of 30 or 31 rather than the normal 32 chromosomes of the species (Mitra 1959). However, these changes have not interferred with the fertility or the combining ability of the Russian clones, which are among sdme of the best in crosses with tall beardeds to produce wanted horticultural traits.

The pumilas are vanishing from their natural habitats, plucked from the hills around Vienna by ruthless picnickers; erased from the Balkans by the close cropping of sheep and goats. Named or numbered clones listed in the Eupogon Iris Species in Cultivation (MIS 1970) are becoming difficult to locate. Many of the most unusual , color forms, such as Kurzmann's 'Lilablanka', which has strong orchid standards and white falls, have proved impossible to maintain in American gardens. Thus we may well be thankful that

====================================================================================================== Figure 3. Idiogram of the gametic chromosomes of I. italica (2n=40), showing its postulated origin from the diploids, I. pallida Dubrovnik (2n=24) and I. pseudopumila (2n=16). Garden Irises.

====================================================================================================== ====================================================================================================== Continued at "The World of Irises" Chapter 9 "Standard Dwarf Irises"

Continued from "The World of Irises" Chapter 7 "Reblooming Irises" ====================================================================================================== For more information on historic Irises visit the Historic Iris Preservation Society at http://www.historiciris.org/

-- BobPries - 2015-12-21
Topic revision: r9 - 24 Jan 2021, WayneMesser
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