Natural, wild PCI hybrid populations

Hybrids (offspring of different species) can occur wherever the ranges of the two or more species overlap. In some cases, this condition may have been stable for hundreds or even thousands of years. Here are two PCI examples:

1. Thompson's Iris.     Iris innominata is a narrow-leaf, delicate, golden-flowered iris living in the dry oak/pine uplands of southern Oregon and adjacent California. Iris douglasiana is a broad-leaf, robust, mostly lavender-flowered species common along the nearby humid coast. In the area between the two lives a series of iris populations that seems to represent an ancient region of intergradation between different parents.

    Leaving typical I. innominata habitat in Oregon and descending the Smith River Canyon toward the coast along Highway 199, one first finds plants that look like I. innominata but with a slight lavender blush on the petals. The farther one travels, the darker the petals - the veins on the petals become purple rather than reddish brown, the petals lavender with yellow centers, then finally almost entirely purple. By the time the highway leaves the river and turns south in the humid lowland Jedediah Smith Redwood State Park, the plants look almost entirely like I. douglasiana: robust, broad-leaved plants and purple flowers with occasional yellow centers on the petals.
    It may not matter to the iris, but biologists haven't been able to agree whether to treat the populations in this transition zone as a distinct species (Iris thompsoni), or simply as a variable hybrid ( I. douglasiana X I. innominata, or I. X thompsoni).

2. The Marin Iris. The shaded Coastal Range forests north of the Golden Gate in central California are home to a large-flowered, mostly yellow iris that some botanists treat as yellow I. douglasiana. Those familiar with the area know that the story is more complex.

    The Marin iris is a field laboratory of natural hybridization, open to anyone who likes the challenge of a good puzzle. There are at least three parent genepools (purple-flowered I. douglasiana and I macrosiphon and yellow-flowered I. fernaldii), actively mixing their components to find a "best fit" for each microhabitat. As a general rule:

• Flower color is most often pale yellow, but it varies widely. In a small area you can see pure snow-white flowers beside others cream-color or pale yellow, shades of brown to white or yellow with a lavender blush on the petals, or lavender with darker purple veins. When present, the signal spot is usually yellow.
• Yellow-flowered plants mostly live on shaded woodland slopes with only dappled sunlight. A few feet away, in adjacent sunny meadows, you find purple Iris macrosiphon. And the open coastal chaparral / grasslands are the exclusive territory of true Iris douglasiana. At the interface, where one habitat stops and another begins, live the plants with clear features of two or three parents.
• Yellow flowers with 2- to 4-inch long floral tubes are found close to the sunny meadows inhabited by typical I. macrosiphon.
• Typically, the Marin iris plant has the structure of a Douglas iris: rather robust, with broad bifacial leaves (one side shiny, the other dull) and ovaries triangular in cross section and with a nipple-like projection where the tube begins. The other parents have narrower leaves, and you can expect to see plants showing the full range of variation between the two.
• Most Marin iris are single plants, usually not forming clumps like the Douglas iris.
• Marin iris' stalks are usually unbranched; Douglas iris stalks are often branched.

    In different books, you might find the Marin iris labeled simply as yellow I. douglasiana, as a Douglas iris race (I. douglasiana major) or variety (I. douglasiana var. major), as a distinct species: (I. major), or as a hybrid: (I. douglasiana X I. fernaldii). Again, it probably doesn't matter to the iris.

NOTE. A related, scattered group of multiparent hybrids [Iris douglasiana, Iris macrosiphon, and Iris fernaldii] occurs in forested areas south of California's Golden Gate, between San Francisco and Santa Cruz counties. In 1959, Lee Lenz described several populations under the label "Santa Cruz Irises".

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