The Azalea Lace Bug is a pest on rhododendrons, especially in gardens. Some hybrids and species are more susceptible to infection by the pests than others. Try avoid growing plants that are susceptible to these pests. I don't know of a complete list of hybrids/species rhododendrons that are, or are not susceptible though. https://www.inaturalist.org/observations/188059606
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.
Currently (26 Jun 2023) on iNaturalist there is only one record of R. albiflorum south, or west, of Hwy 22 in the Oregon Cascades. That record is from Bugaboo Ridge, Bachelor Mountain. There are currently no observations on iNaturalist south of Hwy 20. According to the Consortium of Pacific Northwest Herbaria (CPNWH) (pnwherbaria.org) Roy C Andrews collected this species on Indian Ridge, Lane County in 1935 and 1938. Other than a specimen from Bachelor Butte made in 1926 by E. Anderson those two records are the furthest south records of R. albiflorum in the Oregon Cascades.
I hope hikers will keep their eyes out for R. albiflorum south of Hwy 20 in the Oregon Cascades. The plants will probably be growing in somewhat damp areas well above 4,000' elevation, along rocky ridge lines, or near streams, lakes and meadow edges, possibly hiding in plain sight with Vaccinium spp.
In North-east Oregon they are currently known only from the Elkhorn Mountains, but not in the Wallowas, which seems odd since R. columbianum (formerly Ledum glandulosum) is found in the Wallowas, but not the Elkhorns. R. menziesii is apparently not found in either the Elkhorns, or the Wallowas since there are no records of this species on either iNaturalist, or in the CPNWH database from either of those locations. It is however found fairly close by in Idaho. Keep your eyes open!
Although we are well past the peak of hybrid rhododendron blooming period there are still some that are late bloomers. And there are some that will get reported as our native "Rhododendron macrophyllum" on iNaturalist.
Things to consider when reporting rhododendrons on iNaturalist. Rhododendrons did not evolve in savannas or deserts and are not found in those habitats. Rhododendrons are a very popular garden plant and there are many many hybrids, and cultivars, on the market. Rhododendrons found in private gardens are not wild, or species rhododendrons. Rhododendrons in public, and botanic, gardens are not wild. Rhododendrons found in wild urban parks may not be wild, such as Forest Park, Portland, OR and Sequoia Park, Eureka, CA, are not wild plants. A rule of thumb is that any rhododendron in an urban setting is probably not going to be wild, and possibly not Rhododendron macrophyllum.
Rhododendron macrophyllum has been used as a parent plant with some hybridizers, but it is not widely used, and most commercially available hybrids don't have it as a parent. It is sometimes sold in Native Plant section of nurseries, but it is not easily grown in the summer dry and warm lowlands surrounding the Willamette Valley, or Rogue Valley around Ashland/Medford.
It's in a name! Macrophyllum simply means big leaf. Macro = big, phyllum = leaf; and phyllum is pronounced: fill-um, not fy-lum.
There are a few extremes in coloring, but R. macrophyllum flowers tend to be pale pink and the pistil is a dark pink; the spots on the upper portion of the flower are also generally a bronzy color. There are variations. I have an album on flickr that shows some of the R. macrophyllum flowers I have photographed. More continue to be added. It can be seen thru this link: https://www.flickr.com/photos/ujelang/albums/72177720299414513
Enjoy the photos, but they may not be used without prior permission. And enjoy looking for, and finding, Oregon's wild native rhododendrons, there are five of them: R. albiflorum, columbianum, macrophyllum, and menziesii, . And don't forget to add them to iNaturalist.
There is a good discussion about leaf color on Rhododendron macrophyllum at this observation:
https://www.inaturalist.org/observations/123928264#activity_comment_58fc6cb6-cc34-4530-b006-9527d71707f2
I have compiled a collection of R. macrophyllum flower photos in an album on flickr, which can be seen via this link: https://www.flickr.com/photos/ujelang/albums/72177720299414513/with/247233154/
This album shows the wide variations in R. macrophyllum flowers. In time I will make an album of pink rhododendron flowers that are not R. macrophyllum.
R. macrophyllum is seldom grown in gardens, and now seldom used by hybridizers. It has happened. However, any plant not found in the wild is there by human means; plants found in gardens, state park visitors' center parking lots, college campuses, 'wild' city parks, are all suspect.
Three books of interest:
Greer, Harold E., 1996. :Greer's Guidebook to Available Rhododendrons, species & hybrids" (can sometimes be found on Powells Books, Amazon, ebay.)
van Gelderen, D.M. and J.R.P. van Hoey Smith. 1992. "Rhododendron Portraits". Timber Press.
Nelson, Sonja (ed). 2001. "The Pacific Coast Rhododendron Story. The hybridizers, collectors and Gardens." Binford & Mort Publishing.
The Rhododendron Species Botanic Garden journal 'Rhododendron Species', 2022, Vol. 17 has recently come out. It contains several articles of interest to Pacific NW botanists.
Rhododendron subsection Ledum, by Will Clausen talks about the Trapper Teas which were formerly in the genus Ledum. Oregon has only one species in this group and that is R. columbianum, which is found in the coast ranges and Siskiyou/Klamath Mountains, and in the Wallowa Mountains - but not in the Cascades. Washington State however has three species: R. columbianum, groenlandicum and neoglandulosum.
Emily Joseph has an article "Botanizing in the Biotic Communities of the Olympic Mountains" which is very interesting.f
For those interested in a recently described new species of Rhododendron there is an article on R. smokianum, Bauer & Albach, by Ralf Bauer. This species is found in a limited area in the Great Smoky Mountains, USA.
More information about the RSBG can be found on their website: https://rhodygarden.org/ This garden is a must visit garden for anyone interested in studying rhododendrons. However, any rhododendron found there isn't wild!
We went for a hike on August 23, 2021 to Umbrella Falls, Mount Hood, Mount Hood National Forest starting at the Elk Meadows Trailhead and then up to the falls on the Umbrella Falls Trail. Two known small patches of R. albiflorum were noted along Elk Meadows Trail at an elevation of about 4550 ft in rills (small gullies) above (west of) the trail. A third patch, at an elevation of about 4575 ft, was noted a hundred or so yards west of the Elk Meadows Trail north of the Umbrella Falls Trail. And finally a fourth patch as noted at about elevation 5125 near the Hood River Express ski lift.
At the first location north of the Elk Meadows Trailhead parking flowering had taken place as evidenced by many fruiting bodies. A good photo was obtained showing the location of this year's flowers on the stem above last year's seed pods. R. albiflorum is unique among Rhododendrons in that flowering takes place on the previous year's stem, and not from a terminal bud as in other Rhododendrons. see:https://www.inaturalist.org/observations/92326390
No flowering was evidenced at the 2nd location. see: https://www.inaturalist.org/observations/92503915
At the third location on the lower Umbrella Falls we noted foliage eaten by caterpillars, aphids, and later with microscopic investigation spider mites and an interesting large aphid, as well as two ubiquitous (for R. albiflorum) fungal infections. see: https://www.inaturalist.org/observations/92325595 which includes links to additional related observations.
The fourth and highest elevation observation on 8/23/21 (see: https://www.inaturalist.org/observations/92321447 and: https://www.inaturalist.org/observations/92316642 ) had plants growing in full sun in the ski runs and plants growing in shade. Those growing in conditions with more light have leaves that tend to have wavy/crinkly appearances, while those growing in shadier conditions have leaves that are flat.
There is quite a bit of variation within Pacific Rhododendron. DNA studies indicate there are about 4 clades in plants sampled from north+western California , north to Canada. See;
https://scholar.lib.vt.edu/ejournals/JARS/v60n1/v60n1-xi.htm
Prior to that two members of the American Rhododendron Society explored the Oregon Cascades near Detroit, Oregon for a few years trying to find plants with color variations. Their, and others', findings indicate the color of Pacific Rhododendron can range from white to dark pink. Summaries of, including photographs of color variations, their field trips can be found in the Journal of the American Rhododendron Society:
https://scholar.lib.vt.edu/ejournals/JARS/v40n2/v40n2-boge.html
https://scholar.lib.vt.edu/ejournals/JARS/v41n2/v41n2-boge.html
and
https://scholar.lib.vt.edu/ejournals/JARS/v42n3/v42n3-boge.html
I've been hoping to explore the range of R. albiflorum in the Oregon Cascades this year, hoping to answer the question does it still exist in areas where it has been collected, and what is the health of those populations? The Consortium of Pacific Northwest Herbaria website ( https://www.pnwherbaria.org/data/results.php?DisplayAs=WebPage&ExcludeCultivated=Y&GroupBy=ungrouped&SortBy=Year&SortOrder=DESC&SearchAllHerbaria=Y&QueryCount=1&IncludeSynonyms1=Y&Genus1=rhododendron&Species1=albiflorum&State1=oregon&Zoom=4&Lat=55&Lng=-135&PolygonCount=0 ) was used to find location data, including as follows:
Clackamas County: Veda Lake
Jefferson and Marion Counties: Olallie Lake Scenic and Mount Jefferson Wilderness Areas.
Linn County: Forest Road 2234, Bruno Meadows, Willamette National Forest and Bachelor Mountain.
Lane County: Scott and Scout Lakes, Indian Ridge, Middle Sister
Deschutes County: Bachelor Butte.
Grant County (?): Mount Ruth.
There are many recent reports on iNaturalist of the species around Mount Hood and Mount Jefferson areas and a few from the Elkhorn Mountains. In the Cascades there aren't any recent reports of the species south of Mount Jefferson; and none in the Wallowa Mountains of northeast Oregon. Does the species not exist in the Wallowas? see: https://www.inaturalist.org/observations?place_id=10&subview=map&taxon_id=126556
Much of the area around Mount Jefferson was seriously burned in 2020 from the Lionshead Fire so access to the area will be problematic for possibly several years. Since fires may be a continuing issue for quite awhile I am hoping that observers will make note of where they find R. albiflorum in Oregon, and post those observations on iNaturalist.
