Creme/yellow irises in the Northwest are difficult to identify. This is made even more difficult because several of the species hybridize. Shasta iris (Iris tenuissima) closely resembles yellowleaf iris (Iris chrysophylla) and will hybridize with the yellowleaf iris.
Shasta iris is a perennial native endemic to the Northern California foothills around the upper end of the Central Valley and the southern Klamath and Cascade Ranges. The Shasta iris habitat is shaded, duff-covered forests and small, sunny openings in oak/pine woodlands between 300 and 6,000 feet.
I believe, but cannot be absolutely certain, that Leonard and I found Shasta iris plants near the Gregory Campground near Lake Shasta (Shasta County CA). The type specimens of Shasta iris were discovered near the Pit River Ferry, a location currently under the east arm of Lake Shasta. The Shasta iris in the photographs were found nearby.
Other characteristics used for identification of these Shasta irises include:
*a flower stem usually greater than 4 inches in length,
*the floral tube enlarged at the upper end,
*the floral tube enclosed by spathes,
*the sepals (fall) and petals (standard) spread outward and appear flat,
*the pistil is a highly modified style arm (connects stigmatic tip to the ovary),
*the sepals and petals are very slender with wavy or ruffled edges and brittle (break easily),
*the sepal/petal veins are dark yellow or lavender or reddish-brown,
*the long, narrow style crests are usually turned backward,
*the stigma is tongue-shaped,
*the basal leaves are upright and slightly reflexed with a pink to red base, and
*many leaves taller than the flowers.
The close resemblance between yellowleaf iris and Shasta iris can be see by comparing the Shasta iris photographs with my previous post on yellowleaf iris. (“Yellowleaf Iris” on 08-10-2016)
The species name means “very slender” and refers to the narrow petals and sepals. Other common names for Shasta iris include long-tube iris and slender iris.