Flora of North America species comparison

R. C. Foster (1937) named several varieties of Iris douglasiana, about which L. W. Lenz (1954) said, “This is a widespread and extremely variable species whose total variability is being increased due to introgressive hybridization between it and other species with which it has come into contact. Well marked and distinct geographic races cannot be detected; however, pronounced variations are to be found within a single population. For these reasons no attempt is made here to segregate taxa within such a polymorphic species.”

Iris douglasiana hybridizes with I. bracteata, I. chrysophylla, I. fernaldii, I. hartwegii, I. innominata, I. macrosiphon, I. munzii, I. purdyi, I. tenax, and I. tenuissima. The natural hybrid between I. douglasiana and I. innominata has been designated as Iris ×thompsonii R. C. Foster and the garden hybrid as Iris ×aureonympha E. H. English.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Iris germanica is considered to have been a natural hybrid between I. pallida and I. variegata Linnaeus, both of which also have the chromosome number 2n = 24. Whenever an interbreeding population of a fertile natural hybrid occurs, the plants can be expected to exhibit characters varying from one parental extreme to the other, and this is certainly true in the case of I. germanica. Iris pallida has striking silvery spathes subtending the flowers, whereas I. variegata has completely green or purplish, herbaceous spathes. Usually I. germanica has the spathes green or purplish at the base with scarious margins. Since I. pallida is up to 1 m tall and I. variegata is only up to 4 dm tall, I. germanica would be expected to be intermediate in height (this is true), but the forms have subsequently been selected for greater height and thus have become established as the “tall bearded irises.”

The perianths of Iris pallida are primarily blue, but one form had the blue pigment limited to stipples or stitches on the margins of both sepals and petals, and this recessive pattern was carried over into I. germanica. The perianths of I. variegata are yellow, with the veins of the sepals marked with a dark blue-violet that gives, along with the yellow background, a purple or brown effect. In some forms, the pigment of these veins spreads over most of the surface of the sepals, leaving only a small band of background color along the margins. In I. germanica, if this pattern introduced from I. variegata is added to a light blue-violet background, the petals remain light blue and the sepals become a very dark violet with light blue margins; this form has been called I. neglecta Hornemann. If the pattern is added to a white flower, the result has been called I. amoena de Candolle. A form in which the dark blue veins were replaced by white has been named I. leucographa Kerner. Another form in which this white pigment had spread to produce a large white area on the sepals with a narrow yellow border has been called I. flavescens Delile. All of these forms were known early in the breeding of the garden cultivars of I. germanica and added greatly to their popularity.

J. C. Wister (1927) said that Iris pallida and I. variegata were the only species involved in the production of I. germanica until about 1889, when Sir Michael Foster of England had several large-flowered irises sent to him from the eastern part of the Mediterranean: I. cypriana Foster & Baker, I. trojana A. Kerner ex Stapf, and I. mesopotamica Dykes. These he crossed with the best of the I. germanica forms that he had. He didn’t know it at the time, but these Mediterranean species were tetraploids, and with them he began to produce larger plants and more different patterns, which changed the entire direction of iris breeding. Since that time, many other species from Europe and Asia have been brought into the breeding: I. subbiflora Brotero, I. humilis M. Bieberstein, I. reichenbachii Heuffel, I. imbricata Lindley, I. attica Boissier & Heldreich, I. aphylla Linnaeus, I. albicans Lange, and many others. The plants resulting from hybridization with those other species can not be considered as I. germanica, but must have another name: I. ×conglomerata N. C. Henderson has been proposed.

(Discussion copyrighted by Flora of North America; reprinted with permission.)