4b.2d. Iris (subg. Limniris, sect. Limniris) ser. Californicae (Diels) G. H. M. Lawrence, Gentes Herb. 8: 360. 1953.
Iris subsect. Californicae Diels in H. G. A. Engler and K. Prantl, Nat. Pflanzenfam. ed. 2, 15a: 501. 1930
Stigmas triangular or bilobed. Capsules 3-ribbed, 3-cornered, or cylindrical. Seeds without aril or raphe.
Species 11 (11 in the flora): w United States.
Series Californicae presents some of the most complex taxonomic problems in all of our American irises. All but one species of the series have produced naturally occurring primary hybrids with other species of the group, the one exception being Iris munzii. Two have hybridized with only one other species of the group: I. bracteata with I. chrysophylla, and I. hartwegii with I. macrosiphon. Horticulturally, primary hybrids involving every one of the species have been produced and introduced into gardens. Iris douglasiana has been hybridized with all ten of the others. Only one of the primary hybrids has been given a nothospecific name: I. ×thompsonii (I. douglasiana × I. innominata).
All of these species have 2n = 40. The primary hybrids that have been studied cytologically have shown no significant abnormalities during meiosis, and most of them have had a high degree of fertility. In turn, primary hybrids have been crossed with others, as well as with yet other species, over and over again. Many of these multispecific hybrids have been given cultivar names, and have been propagated vegetatively and widely dispersed over those areas of the country in which they are hardy.
L. W. Lenz (1959) considered very carefully the role of introgressive hybridization within this group. Since every species in the series has the same chromosome number and a great percentage of the hybrids are fertile, as the ecological barriers are decreased or eliminated by the efforts of man, introgression will increase as more and more are brought into contact with others. In considering Iris tenax subsp. klamathensis, Lenz remarked, “This subspecies belongs with the I. tenax–hartwegii–munzii complex and it is most closely related to I. tenax. Indeed in many ways it might be considered as a member of that species. However, there are certain morphological differences, most important of which is the difference in perianth-tube length.” Are the differences due to introgression with some of the other species? Should this be separated as a nothospecies? The same questions could be asked regarding the four subspecies of I. hartwegii. Lenz concluded that “From present available evidence it would appear that primary speciation in the Californicae has taken place principally, though perhaps not exclusively, through ecological isolation of sympatric forms and there has been little or no chromosomal re-patterning within the group. As a result, the species possess the potential of producing vigorous and fertile hybrids when any breakdown occurs in the ecological barriers separating the species. When this does happen, one of the possible results is the merging of separate species into a single interbreeding population providing the isolating barriers are altered sufficiently.” This he termed “secondary speciation.” He went on to observe that “Opposed to the mass fusion of two species into a single interbreeding population is the mere trickle of genes across an interspecific barrier which is manifest in the production of an occasional hybrid. Between the two extremes there can be every intermediate stage.”
Lenz, L. W. 1958. A revision of the Pacific Coast irises. Aliso 4: 1–72. Lenz, L. W. 1959. Hybridization and speciation in the Pacific Coast irises. Aliso 4: 237–309.