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54-615: It is adjacent to the Pacific Bonsai Museum. The organization was founded in 1964 by members of the American Rhododendron Society (ARS) after a visit to Britain by Dr. Milton Walker. Walker was interested in importing cuttings from the best rhododendron plants in the wild as well as public and private gardens. He learned that he could not import cuttings directly from Europe due to American regulations. Canada allowed imports from Europe. Walker asked

108-468: A chromosome number of x=13, fruit that has a septicidal capsule , an ovary that is superior (or nearly so), stamens that have no appendages, and agglutinate (clumped) pollen . Rhododendron is the largest genus in the family Ericaceae , with over 1,000 species, (though estimates vary from 850 to 1,200) and is morphologically diverse. Consequently, the taxonomy has been historically complex. Although Rhododendrons had been known since

162-431: A cladistic analysis. They confirmed that the genus Rhododendron was monophyletic , with subgenus Therorhodion in the basal position , consistent with the matK studies. Following publication of the studies of Goetsch et al. (2005) with RPB2 , there began an ongoing realignment of species and groups within the genus, based on evolutionary relationships. Their work was more supportive of Sleumer's original system than

216-452: A sister to all other rhododendrons. The small polyphyletic subgenera Pentanthera and Azaleastrum were divided between two clades. The four sections of Pentanthera between clades B and C , with two each, while Azaleastrum had one section in each of A and C . Thus subgenera Azaleastrum and Pentanthera needed to be disassembled, and Rhododendron , Hymenanthes and Tsutsusi correspondingly expanded. In addition to

270-457: A hierarchy of subgenus, section, subsection, and species. Terminology from the Sleumer (1949) system is frequently found in older literature, with five subgenera and is as follows; In the later traditional classification, attributed to Chamberlain (1996), and as used by horticulturalists and the American Rhododendron Society , Rhododendron has eight subgenera based on morphology , namely

324-909: A lesser degree in the Mountainous areas of North America and Western Eurasia . Subgenus Tsutsusi is found in the maritime regions of East Asia (Japan, Korea, Taiwan, East China ), but not in North America or Eurasia. In the United States, native Rhododendron mostly occur in lowland and montane forests in the Pacific Northwest , California , the Northeast , and the Appalachian Mountains . Rhododendron ponticum has become invasive in Ireland and

378-419: A new subgenus was created by elevating subgenus Azaleastrum section Choniastrum to subgenus rank. Subgenus Pentanthera (deciduous azaleas) with its four sections was dismembered by eliminating two sections and redistributing the other two between the existing subgenera in clades B ( Hymenanthes ) and C ( Azaleastrum ), although the name was retained in section Pentanthera (14 species) which

432-413: A single section, and some sections only a single subsection. Shown here is the traditional classification, with species number after Chamberlain (1996), but this scheme is undergoing constant revision. Revisions by Goetsch et al. (2005) and by Craven et al. (2008) shown in ( parenthetical italics ). Older ranks such as Series (groups of species) are no longer used but may be found in the literature, but

486-418: A subgenus of Rhododendron . In 1987 Spethmann, adding phytochemical features proposed a system with fifteen subgenera grouped into three 'chorus' subgenera. A number of closely related genera had been included together with Rhododendron in a former tribe, Rhodoreae. These have been progressively incorporated into Rhododendron . Chamberlain and Rae moved the monotypic section Tsusiopsis together with

540-443: A week collecting roots, wood, seeds and cuttings which would take them over a year to analyze. One of the founding members of the society Lawrence Pierce and his wife Isabel Colman Pierce received a gold medal from the American Rhododendron Society . The Royal Botanic Garden Edinburgh named a rhododendron species piercei for him. The Edinburgh Society named a rhododendron hybrid Isabel Piece after Isabel Colman Piece. In 2007

594-472: Is a genus of shrubs and small to (rarely) large trees , the smallest species growing to 10–100 cm (4–40 in) tall, and the largest, R. protistum var. giganteum , reported to 30 m (100 ft) tall. The leaves are spirally arranged; leaf size can range from 1–2 cm (0.4–0.8 in) to over 50 cm (20 in), exceptionally 100 cm (40 in) in R. sinogrande . They may be either evergreen or deciduous . In some species,

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648-547: Is a non-profit organization whose mission is to encourage interest in, and disseminate information about, the genus Rhododendron . Members' experience ranges from novice to expert. The society provides a means through which people interested in rhododendrons and azaleas can communicate and cooperate with others via its publications, events, local and regional meetings and international conferences. Society activities include public education, plant sales, flower shows, seed exchanges, and scientific research. It has chapters throughout

702-515: Is a very large genus of about 1,024 species of woody plants and in the heath family (Ericaceae). They can be either evergreen or deciduous . Most species are native to eastern Asia and the Himalayan region, but smaller numbers occur elsewhere in Asia, and in North America, Europe and Australia. It is the national flower of Nepal , the state flower of Washington and West Virginia in

756-458: Is subgenus Rhododendron , containing nearly half of all known species and all of the lepidote species. For a comparison of the Sleumer and Chamberlain systems, see Goetsch et al. (2005) Table 1. This division was based on a number of what were thought to be key morphological characteristics. These included the position of the inflorescence buds (terminal or lateral), whether lepidote or elepidote, deciduousness of leaves, and whether new foliage

810-643: Is the best collection of rhododendron species on the planet. In 2015 a RSBG sponsored tour of India led by Executive Director & Curator Steve Hootman were trapped for two days by a Himalayan landslide. They were able to escape by footpath led by the local police and military. While on the expedition they "recorded about 20 different species of rhododendron in the area, including a newly discovered species". Scientists from Holden Arboretum in Kirtland, Ohio visited RSBG in 2015 to take samples to investigate physiological diversity among Rhododendron species. They spent

864-733: The Maritime Southeast Asia from their presumed Southeast Asian origin to Northern Australia, with 55 known species in Borneo and 164 in New Guinea . The species in New Guinea are native to subalpine moist grasslands at around 3,000 metres above sea level in the Central Highlands. Subgenera Rhododendron and Hymenanthes , together with section Pentanthera of subgenus Pentanthera are also represented to

918-591: The Solomon Islands . The centres of diversity are in the Himalayas and Maritime Southeast Asia , with the greatest species diversity in the Sino-Himalayan region, Southwest China and northern Burma , from India – Himachal Pradesh , Uttarakhand , Sikkim and Nagaland to Nepal , northwestern Yunnan and western Sichuan and southeastern Tibet . Other significant areas of diversity are in

972-529: The United Kingdom . It is an introduced species, spreading in woodland areas and replacing the natural understory. R. ponticum is difficult to eradicate, as its roots can make new shoots. A number of insects either target rhododendrons or will opportunistically attack them. Rhododendron borers and various weevils are major pests of rhododendrons, and many caterpillars will preferentially devour them. Rhododendron species are used as food plants by

1026-452: The larvae ( caterpillars ) of some butterflies and moths ; see List of Lepidoptera that feed on rhododendrons. Major diseases include Phytophthora root rot, stem and twig fungal dieback. Rhododendron bud blast, a fungal condition that causes buds to turn brown and dry before they can open, is caused by the fungus Pycnostysanus azaleae , which may be brought to the plant by the rhododendron leafhopper, Graphocephala fennahi . In

1080-438: The nursery trade. Rhododendrons can be propagated by air layering or stem cuttings. They can self-propagate by sending up shoots from the roots. Sometimes an attached branch that has drooped to the ground will root in damp mulch, and the resulting rooted plant then can be cut off the parent rhododendron. They can also be reprodcued by seed dispersal - or by horticulturalists collecting the spent flower buds and saving ad drying

1134-659: The 1,100 different rhododendron species that presently existed in the world. In 2019 the Weyerhaeuser Company was sold to Industrial Realty Group (IRG) and planned to develop the Woodbridge Corporate Park. RSBG told the Federal Way Mirror that it was negotiating a new lease and had no plans to go anywhere. The owners of IRG said they are committed to working with RSBG and "have an excellent working relationship" with them. This

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1188-604: The American Rhododendron Society awarded the gold medal to co-director Steve Hootman for his work in conservation and education, calling him one of the "foremost international plant hunters of the late 20th and early 21st centuries ... and among the most knowledgeable people in the world on the genus Rhododendron ". 47°17′34″N 122°18′08″W  /  47.2928°N 122.3023°W  / 47.2928; -122.3023 American Rhododendron Society The American Rhododendron Society ( ARS )

1242-503: The American Rhododendron Society still uses a similar device, called Alliances The system used by the World Flora Online as of December 2023 uses six subgenera, four of which are divided further: Species of the genus Rhododendron are widely distributed between latitudes 80°N and 20°S and are native to areas from North America to Europe , Russia , and Asia , and from Greenland to Queensland , Australia and

1296-487: The Edinburgh group, placing more emphasis on the lepidote characteristics of the leaves, united all of the lepidote species into subgenus Rhododendron , including four of Sleumer's subgenera ( Rhododendron , Pseudoazalea , Pseudorhodorastrum , Rhodorastrum ). In 1986 Philipson & Philipson raised two sections of subgenus Aleastrum ( Mumeazalea , Candidastrum ) to subgenera, while reducing genus Therorhodion to

1350-522: The Garden include the Victorian Stumpery, Himalayan Blue Poppy Meadow, Alpine Rockery Garden and Pond Garden. The Garden Gift Shop and Nursery are located within the Garden. It is open to the public daily, except Mondays. As of 2011, the garden had over 10,000 rhododendron plants. Over 700 species from every continent were represented in the garden. By 2019, the garden had become home to 850 of

1404-741: The UK the forerunner of the Rhododendron, Camellia and Magnolia Group (RCMG), The Rhododendron Society was founded in 1916. while in Scotland species are being conserved by the Rhododendron Species Conservation Group. Both species and hybrid rhododendrons (including azaleas) are used extensively as ornamental plants in landscaping in many parts of the world, including both temperate and subtemperate regions. Many species and cultivars are grown commercially for

1458-614: The United States and Canada, as well as in Denmark , Finland , the Netherlands , Scotland , Sikkim , and Sweden . The ARS publishes a quarterly journal, The Journal of the American Rhododendron Society , covering a wide range of topics including rhododendron culture, propagation techniques, hybridization results, public and private gardens, plant portraits, companion plants, plant hunting explorations, rhododendron scientific research, Society news and events, and much more. The journal

1512-826: The United States, the state flower of Nagaland and Himachal Pradesh in India, the provincial flower of Jeju Province in South Korea, the provincial flower of Jiangxi in China and the state tree of Sikkim and Uttarakhand in India. Most species have brightly colored flowers which bloom from late winter through to early summer. Azaleas make up two subgenera of Rhododendron . They are distinguished from "true" rhododendrons by having only five anthers per flower. The common and generic name comes from Ancient Greek ῥόδον rhódon  'rose' and δένδρον déndron  'tree'. Rhododendron

1566-572: The description of Rhododendron hirsutum by Charles de l'Écluse (Clusius) in the sixteenth century, and were known to classical writers (Magor 1990), and referred to as Chamaerhododendron (low-growing rose tree), the genus was first formally described by Linnaeus in his Species Plantarum in 1753. He listed five species under Rhododendron : R.   ferrugineum (the type species ), R. dauricum , R. hirsutum , R. chamaecistus (now Rhodothamnus chamaecistus (L.) Rchb.) and R. maximum . At that time he considered

1620-597: The garden opened to the public on a limited basis. In 2010 the RSBG opened the 5,000-square-foot Rutherford Conservatory, a climate-controlled greenhouse open to the public that displays a collection of tropical rhododendrons known as vireyas . The vireya section, which has about 319 species, is found almost entirely in Indonesia, Sumatra, Borneo, the Philippine Islands, Malaysia, Thailand and New Guinea. Some of

1674-561: The genus divided into eight sections. Of these Tsutsutsi ( Tsutsusi ), Pentanthera , Pogonanthum , Ponticum and Rhodora are still used, the other sections being Lepipherum , Booram , and Chamaecistus . This structure largely survived till recently (2004), following which the development of molecular phylogeny led to major re-examinations of traditional morphological classifications, although other authors such as Candolle, who described six sections, used slightly different numeration. Soon, as more species became available in

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1728-425: The heath complex in oak-heath forests in eastern North America. They have frequently been divided based on the presence or absence of scales on the abaxial (lower) leaf surface ( lepidote or elepidote). These scales, unique to subgenus Rhododendron , are modified hairs consisting of a polygonal scale attached by a stalk. Rhododendron are characterised by having inflorescences with scarious (dry) perulae ,

1782-520: The later modifications introduced by Chamberlain et al. . The major finding of Goetsch and colleagues was that all species examined (except R. camtschaticum , subgenus Therorhodion ) formed three major clades which they labelled A , B , and C , with the subgenera Rhododendron and Hymenanthes as monophyletic groups nested within clades A and B , respectively. By contrast subgenera Azaleastrum and Pentanthera were polyphyletic , while R. camtschaticum appeared as

1836-492: The monotypic genus Tsusiophyllum into section Tsutsusi , while Kron & Judd reduced genus Ledum to a subsection of section Rhododendron . Then Judd & Kron moved two species ( R.   schlippenbachii and R.   quinquefolium ) from section Brachybachii , subgenus Tsutsusi and two from section Rhodora , subgenus Pentanthera ( R. albrechtii , R. pentaphyllum ) into section Sciadorhodion , subgenus Pentanthera . Finally Chamberlain brought

1890-574: The mountains of Korea , Japan and Taiwan . More than 90% of Rhododendron sensu Chamberlain belong to the Asian subgenera Rhododendron , Hymenanthes and section Tsutsusi . Of the first two of these, the species are predominantly found in the area of the Himalayas and Southwest China (Sino-Himalayan Region). The 300 tropical species within the Vireya section of subgenus Rhododendron occupy

1944-415: The new section Tsutsusi , subgenus Azaleastrum . Genus Menziesa (9 species) was also added to section Sciadorhodion . The remaining small subgenus Therorhodion with its two species was left intact. Thus two subgenera, Hymenanthes and Azaleastrum were expanded at the expense of four subgenera that were eliminated, although Azaleastrum lost one section ( Choniastrum ) as a new subgenus, since it

1998-428: The nineteenth century so did a better understanding of the characteristics necessary for the major divisions. Chief amongst these were Maximovicz 's Rhododendreae Asiae Orientali and Planchon . Maximovicz used flower bud position and its relationship with leaf buds to create eight "Sections". Bentham and Hooker used a similar scheme, but called the divisions "Series". It was not until 1893 that Koehne appreciated

2052-708: The owner of the Royston Nursery, Mary Grieg on Vancouver Island in British Columbia to propagate the cuttings; she worked out an arrangement with the University of British Columbia to facilitate the process. Evelyn Jack, working with the University, grew the plants for two years and, by agreement, kept one plant for the University and sent the other to Oregon for the Society. The Society kept

2106-458: The plants on Walker's property near Eugene, Oregon until 1971 when they were moved to a Board member's home near Salem, Oregon . By 1974, after outgrowing several other sites, the collection moved to its current location, provided by Weyerhaeuser Company corporate headquarters at no cost to the Society. In 1976 a membership and volunteer program were developed. The garden was replanted to group species most closely related to each other. In 1980

2160-475: The presence of scales (lepidote), deciduousness of leaves, and the floral and vegetative branching patterns, after Sleumer (1980). These consist of four large and four small subgenera. The first two subgenera ( Rhododendron and Hymenanthes ) represent the species commonly considered as 'Rhododendrons'. The next two smaller subgenera ( Pentanthera and Tsutsusi ) represent the 'Azaleas'. The remaining four subgenera contain very few species. The largest of these

2214-519: The relationship of the flower buds to the leaf buds, habitat, flower structure, and whether the leaves were lepidote or non-lepidote. While Sleumer's work was widely accepted, many in the United States and the United Kingdom continued to use the simpler Balfourian system of the Edinburgh group. Sleumer's system underwent many revisions by others, predominantly the Edinburgh group in their continuing Royal Botanic Garden Edinburgh notes. Cullen of

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2268-606: The significance of scaling and hence the separation of lepidote and elepidote species. The large number of species that were available by the early twentieth century prompted a new approach when Balfour introduced the concept of grouping species into series . The Species of Rhododendron referred to this series concept as the Balfourian system. That system continued up to modern times in Davidian's four volume The Rhododendron Species . The next major attempt at classification

2322-570: The then known six species of Azalea that he had described earlier in 1735 in his Systema Naturae as a separate genus. Linnaeus' six species of Azalea were Azalea indica , A. pontica , A. lutea , A. viscosa , A. lapponica and A. procumbens (now Kalmia procumbens ), which he distinguished from Rhododendron by having five stamens , as opposed to ten. As new species of what are now considered Rhododendron were discovered, they were assigned to separate genera if they seemed to differ significantly from

2376-577: The two separate genera included under Rhododendron by Chamberlain ( Ledum , Tsusiophyllum ), Goetsch et al. . added Menziesia (clade C ). Despite a degree of paraphyly , the subgenus Rhododendron was otherwise untouched with regard to its three sections but four other subgenera were eliminated and one new subgenus created, leaving a total of five subgenera in all, from eight in Chamberlain's scheme. The discontinued subgenera are Pentanthera , Tsutsusi , Candidastrum and Mumeazalea , while

2430-414: The type species. For instance Rhodora (Linnaeus 1763) for Rhododendron canadense , Vireya ( Blume 1826) and Hymenanthes (Blume 1826) for Rhododendron metternichii , now R. degronianum . Meanwhile, other botanists such as Salisbury (1796) and Tate (1831) began to question the distinction between Azalea and Rhododendron , and finally in 1836, Azalea was incorporated into Rhododendron and

2484-552: The undersides of the leaves are covered with scales (lepidote) or hairs (indumentum). Some of the best known species are noted for their many clusters of large flowers. A recently discovered species in New Guinea has flowers up to six inches (fifteen centimeters) in width, the largest in the whole genus. The accompanying photograph shows it as having seven petals . There are alpine species with small flowers and small leaves, and tropical species such as section Vireya that often grow as epiphytes . Species in this genus may be part of

2538-493: The various systems together in 1996, with 1,025 species divided into eight subgenera. Goetsch (2005) provides a comparison of the Sleumer and Chamberlain schemata (Table 1). Rhododendron Choniastrum Hymenanthes Azaleastrum Therorhodion The era of molecular analysis rather than descriptive features can be dated to the work of Kurashige (1988) and Kron (1997) who used matK sequencing . Later Gao et al. (2002) used ITS sequences to determine

2592-486: The vireyas on display in the Rutherford Conservatory are nearing extinction in their native habitat due to forest degradation . In addition, other rare plants such as wild orchid species and tree ferns are displayed, all growing together as one would see them in their native habitats that span oceans and continents. The conservatory is named for RSBG volunteer Francis C. Rutherford. Additional areas in

2646-534: Was a distinct subclade in  A . In all, Hymenanthes increased from one to two sections, while Azaleastrum , by losing one section and gaining two increased from two to three sections. (See schemata under Subgenera .) Subsequent research has supported the revision by Goetsch, although has largely concentrated on further defining the phylogeny within the subdivisions. In 2011 the two species of Diplarche were also added to Rhododendron , incertae sedis . This genus has been progressively subdivided into

2700-583: Was by Sleumer who from 1934 began incorporating the Balfourian series into the older hierarchical structure of subgenera and sections, according to the International Code of Botanical Nomenclature , culminating in 1949 with his "Ein System der Gattung Rhododendron  L.", and subsequent refinements. Most of the Balfourian series are represented by Sleumer as subsections, though some appear as sections or even subgenera. Sleumer based his system on

2754-402: Was derived from axils from previous year's shoots or the lowest scaly leaves. Following the cladistic analysis of Goetsch et al. (2005) this scheme was simplified, based on the discovery of three major clades (A, B, C) as follows. Clade A Clade B Clade C Sister taxon The larger subgenera are further subdivided into sections and subsections Some subgenera contain only

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2808-589: Was first established in April 1947 as the Quarterly Bulletin of the American Rhododendron Society . The ARS funds research on rhododendrons and azaleas, presents Rhododendron of the Year awards, and gives gold and silver medals to society members for outstanding service. Rhododendron Former subgenera : Rhododendron ( / ˌ r oʊ d ə ˈ d ɛ n d r ən / ; pl. : rhododendra )

2862-467: Was moved to subgenus Hymenanthes . Of the remaining three sections, monotypic Viscidula was discontinued by moving R.   nipponicum to Tsutsusi ( C ), while Rhodora (2 species) was itself polyphyletic and was broken up by moving R.   canadense to section Pentanthera ( B ) and R.   vaseyi to section Sciadorhodion , which then became a new section of subgenus Azaleastrum  ( C ). Subgenus Tsutsusi ( C )

2916-411: Was reduced to section status retaining the name, and included in subgenus Azaleastrum . Of the three minor subgenera, all in C , two were discontinued. The single species of monotypic subgenus Candidastrum ( R.   albiflorum ) was moved to subgenus Azaleastrum , section Sciadorhodion . Similarly the single species in monotypic subgenus Mumeazalea ( R.   semibarbatum ) was placed in

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