By the ninetheenth century botanists had created new genera such as Evansia, Hermodactylus, Moraea, Oncocyclus, and Xiphion. Opinion was divided whether to split the genus into several parts or lump them back into Iris. For instance, J. G. Baker separated some such as Moraea and Xiphion from Iris in his Handbook of the Irideae published in London in 1892.
W. R. Dykes clarified the situation by a compromise in his monograph The Genus Iris (Cambridge University Press, 1913; reprinted in 1974 by Dover). Some groupings of species previously made separate genera became sections within the genus Iris. These included Evansia, Oncocyclus, and Xiphion. (Dykes further divided some of these sections of Iris into groups of species.) Others groupings of species remained outside the genus. The Snake's Head Iris, which Linnaeus had called Iris tuberosa, was left in the genus Hermodactylus, and the many moreas (south African irises) placed in Iris by Linnaeus remained the genus Moraea.
L. Diels' classification of the Iridaceae (in Engles and Prantl's Die Naturlichen Pflanzenfamilien, 1930) updated Dykes classification. Subsections were named in the Apogon section (beardless irises).
G. H. M. Lawrence reclassified irises in 1953. An updated classification by Randolph appears in Garden Irises (L. F. Randolph, editor; A. I. S. 1959). Dykes' sections and subsections were shifted up and down into subgenera, sections, subsections, and series, but no irises were shifted into or out of the genus Iris. This classification is used by the American Iris Society.
Rodionenko's 1961 reclassification in The Genus Iris (in Russian, Moscow, 1961) was more ambitious in that he split the genus into five genera: Iris (includes rhyzomatous irises), Xiphium (bulbous irises like Dutch and English irises), Iridodictyum (bulbous irises like reticulata), Gynandriris (just what Linnaeus called Iris sisyrinchium), and Juno (bulbous Juno irises). Below is a summary of Rodionenko's classification of Iris, the other four genera mentioned above, and Hermodactylus. In this classification, a genus may be divided into subgenera, a subgenus into sections, a section into subsections, and a subsection into series. Several species may be included in a series.
Genus Iridodictyum (Reticulata irises)
Genus Juno (Juno irises)
Genus Pardanthopsis (P. dichotoma, Vesper Iris)
Genus Belamcanda (Blackberry Lilies)
Hybrid genus Pardacanda (Pardanthopsis X Belamcanda; P. norrisii, Candy Lilies)
Most of the irises that a gardener would group would be in the beardless iris group or the bearded iris group. The beardless iris group is a very wide group; beardless irises usually won't even crossbreed unless they're closely related. The bearded iris group must be more closely interrelated since many will crossbreed with each other often producing fertile seedlings.
There are several groups of beardless irises recognized by gardeners. In fact, some gardeners are devoted to just one of these groups. Siberian irises (series Sibiricae) and Pacific Coast irises (series Californicae) are two such groups. Some of the Siberians will cross with the Californicas resulting in a hybrid group called Cal-Sibes. Unfortunately, they're nearly always infertile. Japanese irises are bred from a species in the series Laevigatae. Two other groups of beardless irises are the Louisiana irises (series Hexagonae) and the Spuria irises (series Spuriae). In Rodionenko's classification, Spuria irises are placed in a different subgenus (Xyridon) from the other beardless iris mentioned here.
Bearded irises are the most popular irises. The `true' bearded iris hybrids (section Iris) derive from a wide variety of species belonging to the series Pumilaie, mostly smaller irises, and the series Elatae, mostly larger irises. The American Iris Society classifies bearded irises into six groupings based on size: miniature dwarf, dwarf, intermediate, miniature tall, border, and tall. Another, more exotic, group of bearded irises are the Aril irises (section Hexapogon) which includes Oncos (subsection Oncocyclus) and Regelias (subsection Regelia). These interbreed with the true bearded iris to produce what are called Arilbred irises.