Species in the Pacific Coast Iris group (PCNI) are fully interfertile with each other, which has helped make such proliferation of garden hybrids with widely varying flower traits possible. This occurs naturally on the West Coast where PCNI are native. In areas where a number of PCI species naturally co-reside, hybrids with intermediate characteristics occur. This also makes positive identification difficult in the field, even for professional botanists.
The following discussions are for three areas where more than two PCNI species overlap in the wild. In these areas, it is not at all uncommon to find no 'good' species, but a proliferation of hybrids with mixed plant and flower traits.
For more information on wild PCI hybrids, refer to Dr. Lee Lenz’s booklet, Hybridization and Speciation in the Pacific Coast Irises, available as a reprint from SPCNI.
Three species of PCNI live around San Francisco Bay. On the north side is the Marin area. This is the area immediately north of San Francisco Bay, from the coast into the Coast Range, in Sonoma and Napa Counties. South of the Bay Area in the Santa Cruz Mountains the same three species are also found. In both areas, plants can be seen with relatively pure species characteristics along with others that are not at all easy to identify. Hybrids between all three species are common, mixing plant size, flower shape and color into new combinations, which can make species determinations very difficult.
The three species growing around the Bay Area are I. douglasiana, I. macrosiphon and I. fernaldii.
I. douglasiana is a strictly coastal species; it is vigorous, evergreen and tall, with well branched flower spikes, bearing up to six or more flowers per spike. Disturbances, such as clear cutting and road building, have helped it spread inland, bringing it into more contact with the other species in this region, and aiding hybridization. The coastal I. douglasiana populations are typically purple-flowered, though whites, pinks, yellows, blues and lavenders also occur.
The latter two species are found in meadows, woodlands and forests. Flower color is extremely variable in I. macrosiphon, from purple to white and yellow; this species prefers sunny slopes. Flower stems are quite short, and are typically buried in tall grasses.
I. fernaldii is taller, and always has creamy yellow flowers. It prefers deeper shade than I. macrosiphon.
Hybrids have a mix of physical traits, including flower shape, flowering stem length, flowering time, and leave size. It is often simpler to recognize these as part of a larger species complex than it is to identify each of the known species in this area.
The greatest number of PCNI species is found in northern California and southern Oregon, where several mountain ranges come together along with a patchwork of serpentine and normal soils, and a wide range of elevations and microclimates, all combining to create the ideal workshop for blending species in variable growing conditions into new combinations.
The mountain ranges include the southern Oregon Coast Range, Siskiyou Mountains, Klamath Mountains, Trinity Alps and northern California Coast Range. This is a botanically isolated and unique region, with a high number of endemic plant species. Challenging geography and limited access combine to ensure that no botanist can thoroughly know this area. New species and range extensions, particularly of California species northward, are common findings. In Oregon, the counties include Coos, Douglas, Josephine and Siskiyou Counties. In California, the counties include Humboldt, Del Norte and Trinity Counties.
The species in the Klamath-Siskiyou area include: I. bracteata, I. chrysophylla, I. douglasiana, I. innominata, I. tenax and I. thompsonii. Southern Oregon is the southern end of the geographic range for I. tenax, and the northern end of the range for I. douglasiana. All other species occur only in this area. Two other species have very limited distribution here, and do not overlap as much with these six: I. tenuissima and I. bracteata.
I. douglasiana is strictly coastal in its distribution, though as around the Bay Area, disturbance due to logging, road building and urbanization has helped it spread inland and into contact with other species. The coastal I. douglasiana populations are typically purple-flowered, though whites, yellows, blues and lavenders also occur. This species prefers normal (non-serpentine) soils, open sites, and is salt tolerant. It normally occurs on coastal meadows and seacliffs from southern California to southern Oregon.
I. bracteata, I. chrysophylla and I. innominata are commonly found on serpentine soils, which tend to be sunnier and drier than normal soils due to suppression of nutrients that are less available to plant roots.
I. thompsonii and I. tenax prefer normal to transitional, non-serpentine soils. I. thompsonii hybridizes with I. douglasiana and I. innominata. I. thompsonii has been described by some researchers as a stable hybrid between I. douglasiana and I. innominata. More recent work found that it has distinctly different floral structure characters and unique flavonoids, and is therefore a distinct species. It also hybridizes with nearby species, and along some highways a full range of species 1 to hybrids to species 2 can be seen between it and its neighbors, I. douglasiana and I. innominata. I. innominata has yellow flowers. I. thompsonii has purple-blue, cream, white, gray, red and lavender flowers. Both grow in tight clumps with narrow dark green leaves.
I. tenax is the most northerly PCNI, and is generally deciduous, like the most southerly species, I. hartwegii. It prefers normal soils and sunny locations at a range of elevations. Flower color is highly variable in I. tenax, with at least two geographic areas of stable yellow flower color, and all other colors, from white to dark purple, including blues, light to dark, lavender, pink, and red.