Rhododendron distribution questions
There are now three people who have seen the five rhododendrons native to Oregon. Congratulations to @holyegg @mattunitis and @tellittothevoid
R. macrophyllum, as of 4 Aug 2023, has the most observations of any rhododendron in the state with 1,379 observations. It is probably the most mis-identified rhododendron in the state. Many observers see a rhododendron in a garden in western Oregon and think it is R. macrophyllum. If it is growing in a city in the Willamette Valley its not a wild plant, and most likely a hybrid/cultivar. I would refer you to the American Rhododendron Society's website to try and identify rhododendrons found in garden settings.
R. menziesii has the second most number of observations with 279 observations. It is found in the Coast Range south to about Reedsport, but has not been reported south of there, although it does occur in neighboring Del Norte County, CA, south to central Humboldt County. Mock Azalea is also found in the Cascades south in to the Willamette National Forest, but not in the Wallowa or Elkhorn Mountains of north-east Oregon despite it being found in Idaho's Seven Devils mountains on the Idaho side of the Snake River.
R. occidentale comes in third place with 263 observations. It is found in the south-western corner of the state frequently in serpentine derived soils. It is a popular garden plant and some observations, especially in some coastal state parks, may not be wild plants.
R. columbianum, with 229 observations, is found coastally, in the Siskiyous. Over in the Wallowa Mountains of north-east Oregon they are so far the only reported member of the genus Rhododendron from those mountains. It is not found in the Elkhorn Mountains, or Cascades of Oregon. I would refer you to a discussion by Will Clausen in the Rhododendron Species Botanical Garden's journal Rhododendron Species 2022 titled Rhododendron subsection Ledum. It seems that the population in the Wallowas should be a separate species of Rhododendron neoglandulosum because of morphological and genetic differences.
R. albiflorum, not surprisingly, comes in 5th place with only 142 observations in Oregon. There are very few places where someone can drive up to a spot to find them. I know of only one such location on the east side of Mount Hood where they are found growing alongside R. menziesii. Otherwise it will most likely involve a hike to find this species above 4,000' elevation. More work needs to be done to locate the species south of the Mount Jefferson area of the Cascades. They have been collected as far south as Lane County, but there are no observations on iNat south of Mt. Jefferson. They are found in north-east Oregon only in the Elkhorn Mounts where they are the only rhododendron. There are, so far, no nearby records from Idaho although there are 21 observations of this species from that state.
