In an article in our Fall 1979 issue, Ben Hager discussed the bearded irises which provide the most popular garden plants. Here he deals with the large and diverse group of irises without beards, among which many fine ornamental plants are also found.
The wild habitat of bearded irises is limited to the valleys and mountain ranges that lie to the north of the Mediterranean and to mountains and deserts at the northeastern and eastern end of that sea. The distribution of the beardless irises, on the other hand, is a far more extended story. Beardless irises in their many forms and species circumscribe the northern hemisphere, appearing on all continents and, as with many other plant genera, some are represented in the orient with close relatives found on both the west coast and in the eastern part of North America. Beardless irises are found from the southern areas of the temperate zone up to the edges of the frigid arctic. There are beardless irises that flourish in standing water and others that are happy only in desert conditions; many that demand acid soils and some that prefer alkaline.
G.H.M. Lawrence, in the classification provisionally used by the American Iris Society, divides Section Spathula (beardless irises) into three subsections: Subsection Foetidissima with just one species — Iris foetidissima; Subsection Apogon with sixteen series covering a multitude of species; and Subsection Evansia with eleven species.
Iris foetidissima is found in England and continental Europe. It is tolerant of complete shade — the only iris that is — and is grown, or survives, in gardens almost everywhere. It is known for the orange-red seeds that cling to the opened pod.
Of the sixteen series in Subsection Apogon, representatives of only four are widely grown in gardens: Series Sibiricae; Series Spuriae; Series Laevigatae and Series Hexagonae. A fifth, Series Californicae, contains plants of great garden value and hybrids of these are becoming popular throughout the world. They tolerate only a limited range of soil and climate, however, and their cultivation is confined to a few favorable areas and the gardens of specialists prepared to accommodate their particular needs. Further hybridization will almost certainly extend their range of cultivation, for these plants have few equals among garden ornaments.
Cultivation of plants of Series Unguiculares and Subsection Evansia is similarly limited. Of the remaining series, little is known of some of them; some are not cultivated at all, others are assumed to be growing in the wild. Although of considerable charm, others are difficult to obtain, and, in most cases, difficult to maintain.
Subsection Evansia encompasses a group of most appealing irises with native populations centered in China and extending into northern India and Japan, but with three species in the United States: Iris tenuis, narrowly endemic in Oregon; Iris lacustris around the Great Lakes; and Iris cristata from Arkansas to the Atlantic, the latter two growing in gravelly waterways and I. tenuis preferring woodsy humus. These three small flowered irises resemble, and are quite close relatives of, Iris gracilipes in Japan. This group of four species should do well in shaded rock gardens in cooler areas and all are cold hardy.
Growing in Northern India and China are the Evansia irises with aerial rhizomes, fans of gold-green leaves and much branched flower stems carrying many frilly white or pale lavender flowers: Iris confusa, I. wattii, I. formosana (which seems to be an enigma since few have seen it, although it is supposed to grow on Taiwan) and Iris japonica, a self sterile triploid which has gone wild in parts of Japan, spreading by long stolons. A form of this called Iris “Uwodu” was noted as having stolons three to four feet long. No wonder it has traveled throughout Japan, even with no seed to facilitate its spread.
Iris speculatrix is grown by no one, although attempts have been made at its cultivation. It is the most tropical of all irises and is found in Hong Kong.
Iris tectorum, the roof iris of Japan, has China as its native land. This iris, in particular, makes one wonder why it should be classified as beardless, let alone in a Subsection at the very end of Lawrence’s beardless list. The Evansias do not have beards, but they do have what are called crests at the same place on the falls. These crests are irregular cockscomb-like formations, said to be “epidermal proliferations not to be confused with beard hairs.” To the gardener, however, their appearance is a coincidence that raises doubts about classification. Several successful crosses have been made between Iris tectorum and Iris pallida, a bearded iris, but there is no proven record of an Evansia being crossed with a beardless iris. Perhaps we should think of the Evansias, especially Iris tectorum, as being a link between the widely divergent bearded and beardless irises.
Iris milesii has flowers similar in color and pattern to those of Iris tectorum, but they are smaller and on tall branched stems. Iris milesii grows in drier, sunnier locations and is from northern India. It crosses, so far as is known, with nothing but itself.
The group of irises with aerial rhizomes are generally self sterile but crosses between them are common. Elwood Moleseed made many such crosses a few years ago at the University of California. One result of these, a dwarf iris, was recently posthumously named for him.
Culture is simple but exacting. All but Iris tectorum and I. milesii must be grown in pure leaf mould, aged wood shavings, or a mixture of leaf mould and sand. Too much contact with soil results in dwindling and loss of the plants.
Series Sibirica is divided into two subseries on the basis of chromosome counts. From European meadows where we find Iris sibirica of Subseries Sibiricae, then jumping to the eastern Orient to find Iris sanguinea (both have 28 chromosomes), we there pick up the other subseries group, Chrysographes. Subseries Chrysographes includes Iris wilsoni and I. forrestii, the yellow flowered members, and I. chrysographes, I. delavayi, I. clarkei, and l. phragmitectorum with violet to purple colored flowers. All have 40 chromosomes. In spite of the difference in chromosome counts, members of these two subseries will intercross, producing, almost always, infertile offspring. However, at least one such hybrid of recent origin is fully fertile.
We can postulate that the Series Sibiricae reaches across the Pacific Ocean to the west coast of North America where we find the eleven species of the Series Californicae. In recent years a great number of hybrids have been obtained by crossing plants of the Series Sibiricae (especially those of Subseries Chrysographes) with those of the Series Californicae. The offspring are sterile, but attractive and worthy of space in gardens. The first Dykes Medal was given in 1927 to ‘Margot Holmes’, an iris from such a cross made in England. These hybrids have attracted enough attention to be given the group name of Cal-Sibe and are listed in the catalogs of nurserymen in the Northwest, although they grow with reluctance, if at all, in California. The northern California coast might meet their requirements — they do grow in England.
This interfertility shows the close relationship between Series Californicae and Series Sibiricae. And, as a further consideration, a hybrid was described (with convincing photographs) of a cross between an iris of Series Californicae and Iris setosa of the Series Tripetalae. Iris setosa is the near-arctic iris whose range covers the area from Labrador, through Canada to Alaska and into Siberia — the only species to span two continents. It requires the cold of its austere northern habitat to grow well. South of the state of Washington, it is not to be considered a satisfactory garden subject: Nevertheless, in Georgia and the Carolinas is a closely related iris of the same series — Iris tridentata. Undoubtedly a glacial emigrant, the seeds of Iris setosa were probably pushed down by glaciers. In one of those dramatic examples of evolution, Iris tridentata emerged, adapted to the humid hot swamps of those southern regions.
Plants of Subseries Chrysographes are interesting and often spectacular in flower, but are not widely grown as garden plants because of their exacting demands for moisture and rich acid soils. They are also more dependent on low temperatures than temperate zone winters can guarantee.
With the two species of Subseries Sibiricae, however, we are in gardener’s territory. They and their hybrids have furnished us with some of the most satisfactory garden irises available. The Siberians are moist meadow plants in nature and at least a partial recreation of such a situation is advisable, but boggy conditions are to be avoided. Good drainage with a fairly constant moisture supply and a slightly acid soil will make them happy. The immediate coastal areas of Northern California and the marine-influenced parts of Washington and Oregon would have such conditions, but the inland and southern areas of this territory tend to have alkaline soil and water. Additions of a little sulphur and lots of organic matter should correct such soils to the benefit of Siberian irises. A sprinkling of camellia food a couple of times a year will keep them going if the soil is moist.
Pacific Coast Irises
The species and hybrids of Series Californicae also prefer acid soils. With the exception of Iris douglasiana, a coastal meadow plant, they are woodsy plants that grow in soils with high humus levels and high rainfall. Unlike others of the acid-loving irises the Pacific Coast irises need a summer dry-out — as do most western native plants. These irises would undoubtedly be the darlings of the iris world except for their arbitrary and demanding natures. They are not at all easy to transplant when mature and they are very particular about climate and soil. Abundant growth and flowering on plants of this group is pretty well limited to temperate western coastal areas and coastal mountain ranges. England has proved to have a climate benevolent for them, as have parts of Australia and New Zealand, where many western natives do so much better than they do at home.
Three exceptions to the coastal habitats of plants of Series Californicae are found in the foothills of the Sierra Nevada: Iris macrosiphon, Iris munzii and Iris hartwegii. Brought down to the Central Valley floor these plants are harder to maintain than those of the coastal species. Iris munzii is being widely used in breeding because of its clear blue color, but much remains to be done in combining that color with the robustness of, say, Iris douglasiana.
The wonderfully beautiful flowers of the new hybrids being derived from crosses of Iris innominata, I. bracteata, I. douglasiana and the iris from Oregon and Washington, I. tenax, are without question among the most exquisite of flowering plants. Work by hybridizers must lead toward the development of hardier strains; they should be possible to achieve.
The next two groups of acid-loving beardless irises will all grow in standing water; yet, though some need definite bog-like root-runs, others will grow well in sufficiently irrigated gardens. But, to repeat, they all need acid soil.
The Japanese iris, Iris kaempferi, (strictly, Iris ensata, but I prefer the name in common use) is perhaps the best known of Series Laevigatae. Modern cultivars derived from this species look unlike others in Series Laevigatae, but the wild irises from which the spectacular kinds of today have been developed over the last 300 years by the Japanese, have a strong resemblance to Iris laevigata and were often confused with it. It is interesting to note that today’s marvelous beauties are the results of the selective breeding of one species only. All of the great advances in breeding other irises are the outcome of hybridizing among two or more closely related species.
Pictures of iris gardens in Japan nearly always show Iris kaempferi growing in flooded beds. This has led to the idea that they must be grown in that manner. Such is not the case. The fact is simply that the Japanese flood the beds for picturesque effect. Not that the irises won’t grow in standing water, they obviously will, but they will also flourish in gardens where deep and frequent irrigation is applied during spring and through flowering. Some water is also needed to keep them from drying out completely during the rest of the year. Too boggy a condition can even be harmful to them during the winter dormant season. Japanese irises prefer heavy soils high in fertility and humus.
Iris kaempferi is native to Japan and Korea, as is Iris laevigata, Iris laevigata is strictly a bog plant doing well in very wet locations such as pond edges, and in pots standing in water. This is the iris most often seen in Japanese art; obviously they think highly of it. Iris laevigata has evidently resisted such development as occurred with Iris kaempferi, although it is handsome in itself and many selections of color and form have been named. Considering the superficial similarity between Iris kaempferi and Iris laevigata and their botanical relationship it seems strange that they will not cross, nor are any wild hybrids known. Tetraploidy has been induced in plants of both these species, as it has in Siberian irises.
Iris pseudacorus is the giant of the iris world, making huge clumps four to six feet tall. The bright yellow to cream flowers are showy, but look small by comparison to the monstrous plants and broad leaves. This is the iris representing Series Laevigatae in the streams and lakes of Europe. Seeds, prolifically borne, germinate readily. Streams or lakes where it is introduced are soon lined with seedlings and it has become common throughout the world. It will grow well with regular garden irrigation or in areas of high rainfall but the more moisture it gets the taller it becomes. There are also dwarf forms of it. Cutting the seed pods from the plants before they mature avoids proliferation. Hybrids between Iris pseudacorus and the Japanese iris (Iris kaempferi) are now available. They look more like Japanese irises but have yellow flowers, a color not known in Japanese irises.
Along the Atlantic coast of North America and into the midlands around the Great Lakes are two irises put into Series Laevigatae, some think, simply to find a shelf to store them on. Both are spectacular water-side plants being almost as vigorous as Iris pseudacorus. Iris versicolor from the northern range has the distinction of possessing the highest chromosome count of all irises, 2n =108. It grows less well in moderate climate gardens than does the more southerly Iris virginica which has only 72 chromosomes. (This is still pretty high for an iris — the giant Iris pseudacorus has only 2n =34.) Iris versicolor and l. virginica are interfertile and, surprisingly, the offspring will occasionally produce seed. This is only one of the peculiarities of these species. The seeds of Iris virginica, with their corky coating, have a close resemblance to those of the Louisiana irises of Series Hexagonae. The seeds of Iris versicolor are smaller with a thin, very shiny, mahogany brown covering.
It has been suggested that Iris versicolor arose from an ancient cross of the northerly Iris setosa with Iris virginica. The chromosome count of I. versicolor, 2n =108, perhaps the result of an unreduced gamete, would tend to support this theory. But what kind of family tree does that produce, with l. setosa crossing with irises of Series Californicae which in turn are related to the Siberians? What of the classification of Series Laevigatae and the two American members of it, which certainly resemble members of Series Laevigatae more than they do other irises? Such are the mysteries of iris evolution that may eventually be unraveled by studies of iris cytology and by further breeding.
All of the acid-loving irises so far mentioned, with the exception of the Californicae and Iris virginica are winter dormant — the leaves die down in winter. That, of course, points up the fact that they are native to colder climates. As we look to milder areas such as those occupied by the two exceptions, the pattern changes to one of winter leaf growth with semi-dormant periods in late summer. The so-called Louisiana irises of Series Hexagonae, coming mainly from the Gulf of Mexico coast, will naturally follow this pattern. Our modern garden Louisianas are hybrids between the five species of this Series — some of them natural hybrids collected in the wild. Iris giganticaerulea, the largest species, is entirely coastal and southern; Iris fulva, with terra-cotta red flowers, is much smaller and grows up the Mississippi to southern Illinois; Iris brevicaulis (I. foliosa) can often be found as far north as Indiana, Iris hexagona is more exclusive and grows in a more easterly area from the Carolinas down into Florida. The limited range of Iris hexagona suggests that it is less adaptable and for this reason perhaps, it has been used less in breeding modern hybrids. A recently described species, Iris nelsoni has resulted from introgressive hybridization but was isolated to the extent that it developed its own specific characteristics. The southernmost relatives of this group are all swamp plants. Iris fulva and I. brevicaulis grow on river banks and meadows with less moisture. The Louisiana irises are the greatest contribution from North America to the iris world. Not that they are prettier or more spectacular than the Pacific Coast native irises, but because they can be more widely grown as garden plants. Louisiana irises grow and flower in gardens as far north as the Canadian border, although not as abundantly as in more southern climes. They will grow in standing water year around or in normal garden conditions if the soil is acidified and irrigation is regular and generous. In mild climates they put on most of their leaf growth during the winter and hold their green leaves better through the summer than do others of this growth pattern.
Louisiana irises do not produce flowers in masses as do other irises but present a distinguished display of well spaced flowers on sturdy, branched, two to three foot stems. Here too is the widest range of colors to be found in beardless irises; white, yellow, brown, red, pink, lavender, violet and purple. The truest red in irises is also in flowers of this group.
The irises of Series Spuria, like most of the other beardless irises, need a lot of field work done among the wild populations to straighten out the confusion surrounding them. Fourteen or more species still exist and among those now recognized are four at least that are dwarf, three of intermediate height and the rest are plants three to four feet in height. But the garden irises of today stem mainly from only three of these; Iris ochroleuca, with large white flowers, I. monnieri, described from a garden plant but never found in the wild, and one of the forty-four chromosome irises — which one is not known — that entered breeding lines through an iris mistakenly called ‘Monspur’. The name ‘Monspur’ is made from those of Iris monnieri and I. spuria from which it was thought to be descended. Recent chromosome counts, however, have shown that I. spuria was not involved. I. monnieri has yellow flowers and may be a natural hybrid of I. ochroleuca and a yellow iris from Turkey yet unnamed. These irises, which show only yellow, white and blue in their flowers are, nonetheless, the basis of all large flowered garden varieties of today which have flowers of white, yellow, brown, pink, lavender, deep violet, purple and wine-red. Recently added genes from Iris maritima, I. carthaliniae, I. klattii and I. demetrii — these last two fairly new arrivals from Russia — have brought clearer blues, bi-color patterns and a longer period of summer-green foliage.
Spuria irises have a distribution arching across Europe from Spain to Turkey and southern Russia. Nearly all of those from Europe and southern Russia are dormant in winter whereas those from Turkey are dormant in mid to late summer and start foliage growth in early winter. Most hybrids today are derived from the latter group and are summer dormant. Crossing these with winter dormant irises is giving plants with a longer period of summer green foliage, as this character seems dominant in breeding. Spuria irises, no matter what their region of origin, have similar cultural needs. They must have good drainage with adequate moisture in the spring and fall, but a definite drying-off period from mid July through August. They seem to prefer soils that are high in nutrients and slightly on the alkaline side. The modern hybrids are wonderful garden subjects and have last well as cut flowers. Some of the wild ones charm also.
Other irises that prefer alkaline soil include the one species of the Series Ensatae, from the uplands of central Asia, and those of the Series Longipetalae. Iris biglumis (I. ensata) var. hyacinthina makes an attractive, permanent clump if planted in a well drained, sunny location. It covers itself with small lavender and white flowers in early spring. Series Longipetalae consists of two species, Iris missouriensis and I. longipetala. I. missouriensis, sometimes called the Rocky Mountain iris, extends its range to meadows on the eastern slopes of the Sierra — with a patch in the meadow to the west of Mount Shasta, and others near a couple of lakes in the mountains of southern California and just across the border into Mexico (making it the only iris native to that country). West of that line Iris missouriensis will not grow. In an area From Aromas north to Healdsburg along the eastern slopes of the coastal hills of central California is found I. longipetala. Land in that area is being built over more rapidly every year and except that it can cling to steep hillsides, I. longipetala in the wild is not long for this world.
Iris longipetala is closely related to I. missouriensis but, like most western maritime plants, it grows in the winter months, and grows like a weed (which cattlemen swear it is), whereas I. missouriensis will not grow at all in the same area. Proposals to relegate I. longipetala to the status of a subspecies of I. missouriensis ignore these differences, important to gardeners, and suggest affinities between the plants misleading to those attempting their cultivation.
Iris unguicularis (I. stylosa), the winter iris is worthwhile in gardens that are not too cold in winter. The delicately scented lavender or white flowers are produced from November on, but may be overlooked in the heavy foliage. Many gardeners cut back the leaves in October so that the flowers are seen only with shorter new leaves. This native of Mediterranean shores may not compete for color with spring flowering irises, but in its season there is little to compare with it, especially when it is grown in association with pink flowered saxifrage.
Irises form a large and complex genus. Of the beardless irises alone there is far more to be said than can be included in this short article. The World of Irises, recently published by the American Iris Society, contains information to enthrall an enthusiast for many years. It can be had by sending $15 to the Society c/o Dorothy Howard, Librarian, 226 East 20th Street, Tulsa, OK 74119.
Not everything I have said here is in accord with the “provisional” classification system used in The World of Irises. I have stressed relationships between species suggested by attempts at hybridizing them because it seems to me that if species are interfertile there is a closer relationship between them than investigation of their morphology will reveal. Cytology — the comparison of patterns of genes in plant chromosomes — will tell more, but that road to understanding is a long one.