The Remarkable "Marin Iris"
"The delicacy of forms and the fine shadings of color combine to make the Marin iris one of the chief floral delights of the vernal woodlands." - - John Thomas Howell, Marin Flora (1949).
Forests of the Marin Peninsula in California have been isolated for a long time, perhaps several thousand years since the end of the last Ice Age. A wide belt of pasture and prairie grassland now separates them from related forests to the north and east.
In the shaded woodlands around Mount Tamalpais, genetic material from at least three parental iris stocks combine to form a natural hybrid known as the "Marin iris". Two purple-flowered species are still common: Douglas iris (Iris douglasiana) on the open coastal plain and brushland, and the Ground iris (Iris macrosiphon) of inland grassy hills and meadows. The third parent stock is a yellow-flowered forest species, probably Fernald's iris. Iris fernaldii is widely distributed is the Sonoma Valley and other forested areas to the east, but on the Marin Peninsula, it no longer exists as a pure species.
Sometimes you can pretty well guess the probable parents of a particular plant, especially when the crossing has recently occurred: - A graceful, light brown macrosiphon-like flower in a shady glade just a few steps away from a sunny meadow and some Ground iris; - Or a pale lavender, almost douglasiana-like flower under some streamside shrubs on the Tiburon peninsula above the San Francisco Bay. But in most cases, so many generations have passed, and the gene pools are so thoroughly mixed, that all you can do is stand in awe at the result.
Brian Agron often carries his camera along on bike rides or walks from his home in Fairfax. Most of his iris photos were taken in the area around Lake Lagunitas, on the northern slope of Mt. Tamalpais. Here he shares with us glimpses of the Marin iris' breathtaking variety of form and color.
In some years, pale white iris carpet this Madrone forest like snow.
The surrounding grasslands are no barrier for Marin Peninsula Ground iris (Iris macrosiphon).
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