Of the first two of these, the species are predominantly found in the area of the Himalayas and Southwest China (Sino-Himalayan Region). The species in New Guinea are native to subalpine moist grasslands at around 3,000 metres above sea level in the Central Highlands. [42] In 2011 the two species of Diplarche were also added to Rhododendron, incertae sedis.[43]. 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,[44] Rhododendron has eight subgenera based on morphology, namely the presence of scales (lepidote), deciduousness of leaves, and the floral and vegetative branching patterns, after Sleumer (1980). It is the national flower of Nepal, the state flower of Washington and West Virginia in the United States, the provincial flower of Jiangxi in China and the state tree of Sikkim and Uttarakhand in India. [51] Azaleas are frequently used around foundations and occasionally as hedges, and many larger-leafed rhododendrons lend themselves well to more informal plantings and woodland gardens, or as specimen plants. There are alpine species with small flowers and small leaves, and tropical species such as section Vireya that often grow as epiphytes. They are distinguished from "true" rhododendrons by having only five anthers per flower. [2], The 300 tropical species within the Vireya section of subgenus Rhododendron occupy the Malay archipelago from their presumed Southeast Asian origin to Northern Australia, with 55 known species in Borneo and 164 in New Guinea. A small number, however, possess excellent cold hardiness and grow well in Iowa. Of these Tsutsutsi (Tsutsusi), Pentanthera, Pogonanthum, Ponticum and Rhodora are still used, the other sections being Lepipherum, Booram, and Chamaecistus. [33], A number of closely related genera had been included together with Rhododendron in a former tribe, Rhodoreae. Individual hybrids of rhododendrons have been grafted on to a rootstock on a single rhododendron plant that was found growing in a chalk quarry. [30][31] In 1986 Philipson & Philipson raised two sections of subgenus Aleastrum (Mumeazalea, Candidastrum) to subgenera, while reducing genus Therorhodion to a subgenus of Rhododendron. These have been progressively incorporated into Rhododendron. [11], Rhododendron is the largest genus in the family Ericaceae, with as many as 1,024 species,[12] (though estimates vary from 850 to 1000[13]) and is morphologically diverse. Red-flowered varieties such as Baden Baden (Rhododendron 'Baden Baden') and Scarlet Wonder (Rhododendron 'Scarlet Wonder') stay small and are hardy down to USDA zone 6. A good resource for rhododendron cultivars is Virginia Tech's American Rhododendron Plant Society Registry. Rhododendrons can become quite large, even tree-like. (2005)[2] and by Craven et al. As well as being small, some varieties produce tiny leaves, such as Rhododendron impeditum, with bright blue flowers and hardiness down to USDA zone 5, or Chikor (Rhododendron 'Chikor'), hardy down to USDA zone 6, which bears clear yellow flowers. Maximovicz used flower bud position and its relationship with leaf buds to create eight "Sections". Pompey's soldiers reportedly suffered lethal casualties following the consumption of honey made from Rhododendron deliberately left behind by Pontic forces in 67 BCE during the Third Mithridatic War. Of the three minor subgenera, all in C, two were discontinued. The pot’s size is also important, it shouldn’t be too big. Remember, though, that many rhododendrons can grow from 20 to 30 feet tall, weaving a root system that spreads wider than the top growth, so moving smaller azaleas might be more successful. Choose heat-tolerant kinds. (2005) with RPB2,[2] there began an ongoing realignment of species and groups within the genus, based on evolutionary relationships. Rhododendrons up to 1 foot in size; Otherwise known as miniature Rhododendrons, these variations rarely grow above 12 inches in height. Miniature rhododendrons seldom grow beyond a foot in height. This division was based on a number of what were thought to be key morphological characteristics. These rhododendrons need ample room to grow and should not be planted on small lots or near sidewalks or driveways. Yes, it does! Most rhododendrons thrive in humid climates with mild winters, although there are hardy varieties that survive colder temperatures. The larger subgenera are further subdivided into sections and subsections[45] Some subgenera contain only a single section, and some sections only a single subsection. By contrast subgenera Azaleastrum and Pentanthera were polyphyletic, while R. camtschaticum appeared as a sister to all other rhododendrons. Other significant areas of diversity are in the mountains of Korea, Japan and Taiwan. Everything you need to know about choosing the right rhododendron for you. For a comparison of the Sleumer and Chamberlain systems, see Goetsch et al. R. ponticum is the state flower of Indian-administered Kashmir and Pakistan-controlled Kashmir. How to Grow Dwarf Rhododendrons. [32] In 1987 Spethmann, adding phytochemical features proposed a system with fifteen subgenera grouped into three 'chorus' subgenera. People have been known to become ill from eating honey made by bees feeding on rhododendron and azalea flowers. 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. The nineteenth-century American poet and essayist Ralph Waldo Emerson in 1834 wrote a poem titled "The Rhodora, On Being Asked, Whence Is the Flower", In Joyce's Ulysses, rhododendrons play an important role in Leopold and Molly's early courtship: Molly remembers them in her soliloquy – "the sun shines for you he said the day we were lying among the rhododendrons on Howth head in the grey tweed suit and his straw hat the day I got him to propose to me". Rhododendron maximum, the most widespread rhododendron of the Appalachian Mountains, is the state flower of the US state of West Virginia, and is in the Flag of West Virginia. Rhododendron in botanical garden Pruhonice-Czech republic, Annotated Checklist of the Flowering Plants of Nepal: Rhododendron, The Quarterly Bulletin of the American Rhododendron Society 1947–1981, Journal of the American Rhododendron Society (JARS) 1982–, The Rhododendron, Camellia & Magnolia Group of the Royal Horticultural Society, Rhododendron Species Foundation and Botanical Garden, Royal Botanic Garden Edinburgh: Rhododendrons at the four Gardens, National Rhododendron Gardens Melbourne Australia, https://en.wikipedia.org/w/index.php?title=Rhododendron&oldid=994047924, Plants used in traditional Chinese medicine, Articles containing Ancient Greek (to 1453)-language text, Short description is different from Wikidata, Articles with unsourced statements from June 2020, Articles with unsourced statements from May 2016, Creative Commons Attribution-ShareAlike License. [citation needed], The rhododendron is the national flower of Nepal, where the flower is considered edible and enjoyed for its sour taste. The single species of monotypic subgenus Candidastrum (Rhododendron albiflorum) was moved to subgenus Azaleastrum, section Sciadorhodion. Rhododendrons (Rhododendron spp.) The hardiness range for rhododendrons falls between U.S. Department of Agriculture plant hardiness zones 4 through 8, but each rhododendron has its own hardiness rating, according to Missouri Botanical Garden. Growing rhododendron successfully requires the proper planting spot for the rhododendron bush. They can also go the other direction and be grown as small, manageable plants in containers. Some are in big heads, large bells, some have elongated bells. (2002) used ITS sequences[40] to determine a cladistic analysis. [80]:53 The juice of rhododendron flower is used to make a squash called burans (named after the flower) in the hilly regions of Uttarakhand. Soil preparation is best accomplished in autumn before planting the rhododendron in spring. Rhododendrons are a diverse group of plants that also include both evergreen and deciduous azaleas. Unfortunately, most rhododendrons and azaleas (there are over 900 species and innumerable varieties) cannot be successfully grown in Iowa because of a lack of cold hardiness. 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 next two smaller subgenera (Pentanthera and Tsutsusi) represent the 'Azaleas'. Large-scale commercial growing often selects for different characteristics than hobbyist growers might want, such as resistance to root rot when overwatered, ability to be forced into budding early, ease of rooting or other propagation, and saleability. Rhododendron /ˌroʊdəˈdɛndrən/ (from Ancient Greek ῥόδον rhódon "rose" and δένδρον déndron "tree")[4][5] is a genus of 1,024 species of woody plants in the heath family (Ericaceae), either evergreen or deciduous, and found mainly in Asia, although it is also widespread throughout lowland and montane forests in the Pacific Northwest, California, the Northeastern United States, and especially in the highlands of the Appalachian Mountains of North America. They will rot in standing water. The Species of Rhododendron[26] referred to this series concept as the Balfourian system. In some species, the undersides of the leaves are covered with scales (lepidote) or hairs (indumentum). 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. A Rhododendron bush, is a popular flowering bush and foundation plant, with bright spring blooms. In cold climates, most do better on the north side of a building or on a northwest slope. Following the cladistic analysis of Goetsch et al. Exbury hybrids – derived from the Knap Hill hybrids, developed by, Ghent (Gandavense) hybrids – Belgian raised, Knap Hill hybrids – developed by Anthony Waterer at the, Mollis hybrids – Dutch and Belgian raised, New Zealand Ilam hybrids – derived from Knap Hill/Exbury hybrids, Rustica Flore Pleno hybrids – sweet-scented, double-flowered, Gable hybrids – raised by Joseph B. Gable in, Glenn Dale hybrids – US raised complex hybrids, Indian (Indica) hybrids – mostly of Belgian origin, Kyushu hybrids – very hardy Japanese azaleas (to −30 °C), Oldhamii hybrids – dwarf hybrids raised at, Satsuki hybrids – Japanese raised, originally for, Vuyk (Vuykiana) hybrids – raised in the Netherlands, Azaleodendrons – semi-evergreen hybrids between deciduous azaleas and rhododendrons, This page was last edited on 13 December 2020, at 21:10. Larger commercial growers often ship long distances; in the United States, most of them are on the west coast (Oregon, Washington state and California). There are over 28,000 cultivars of Rhododendron in the International Rhododendron Registry held by the Royal Horticultural Society. The shade-tolerant rosebay (Rhododendron maximum) grows wild from Nova Scotia to Georgia. They usually can be found near the tree edges because they do … [65][66], Rhododendrons are extensively hybridized in cultivation, and natural hybrids often occur in areas where species ranges overlap. Get involved. That system continued up to modern times in Davidian's four volume The Rhododendron Species.[27]. [72] Xiong et al. [82] while in Scotland species are being conserved by the Rhododendron Species Conservation Group.[83]. They like well drained acid soil. Cullen of 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). When to plant rhod… Rhododendron niveum is the state tree of Sikkim in India. Some may be small enough to place at the front of the border. The Royal Horticultural Society is the UK’s leading gardening charity. It is good to start small and up-size your pot every 2 to 3 years (except if you plant to grow your rhododendron in a large pot that is not designed to be moved around). Sometimes plants survive in spite of our treating them poorly. As new species of what are now considered Rhododendron were discovered, if they seemed to differ significantly from the type species they were assigned to separate genera. They are one of the most under rated rhododendron plants available for sale. There are over 800 species of rhododendrons ranging from spreading groundcovers a few inches high to 100 foot tall trees and many thousands of registered, named varieties. [11], Although Rhododendrons had been known since 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. While usually grown as shrubs, they can get very big and take up the space of a small tree. Then they will not grow into a tree or a big bush. How to choose the substrate for growing in pots. For a comparison of the Sleumer and Chamberlain schemata see Table 1 of Goetsch (2005). Rhododendrons are originally a woodland plant and so dappled shade is their native conditions, although Rhododendrons are fairly tough and will grow anywhere in the right (acid) soil. griffithianum. [52], In the Indian state of Himachal Pradesh, rhododendron flowers have been used for some time to make popular fruit and flower wines. Sleumer's system underwent many revisions by others, predominantly the Edinburgh group in their continuing Royal Botanic Garden Edinburgh notes. Many of our competitors only offer smaller sizes, which will take years to reach an appealing height. Some are wild. Information on rhododendrons at the Ericaceae web pages of Dr. Kron at Wake Forest University. 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 gardeners think azaleas and rhododendrons prefer to grow in deep shade. Azaleas make up two subgenera of Rhododendron. [45] The largest of these is subgenus Rhododendron, containing nearly half of all known species and all of the lepidote species. Binfield (Rhododendron 'Binfield') is hardy down to zone 6 and bears clear yellow blooms. Shown here is the traditional classification, with species number after Chamberlain (1996), but this scheme is undergoing constant revision. Pink Rhododendron (Rhododendron campanulatum) is the State Flower of Himachal Pradesh, India. [25] It was not until 1893 that Koehne appreciated the significance of scaling and hence the separation of lepidote and elepidote species. Then look no further than the hardy rhododendron. Genus Menziesa (9 species) was also added to section Sciadorhodion. 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 was a distinct subclade in A. [34] Chamberlain and Rae moved the monotypic section Tsusiopsis together with the monotypic genus Tsusiophyllum into section Tsutsusi,[35] while Kron & Judd reduced genus Ledum to a subsection of section Rhododendron. They like moist, rather cool air. [citation needed], In Daphne Du Maurier's novel Rebecca, the character of Rebecca is associated with "blood red" rhododendrons throughout the novel, perhaps due to the toxic roots of the plant mirroring the poisonous character of Rebecca. These giants include varieties like Caractacus (Rhododendron Caractacus), hardy down to USDA zone 4 and bearing rosy red blooms, according to the American Rhododendron Society, or the purple-flowered Whidbey Island (Rhododendron 'Whidbey Island') hardy down to USDA zone 6. [2][11][30] These consist of four large and four small subgenera. )[41], Subsequent research has supported the revision by Goetsch, although has largely concentrated on further defining the phylogeny within the subdivisions. giganteum, reported to 30 m (100 ft) tall. [80]:51 The flower, fresh or dried, is added to fish curry in the belief that it will soften the bones. [48] It is an introduced species, spreading in woodland areas and replacing the natural understory. Dig a hole as deep as the root ball and 2 times as wide. Sleumer based his system on the relationship of the flower buds to the leaf buds, habitat, flower structure, and whether the leaves were lepidote or non-lepidote. The key is the annual growth rate, up to 60cm per year for the most vigorous and less than 1cm for the slowest growing. [68] Other examples include the PJM hybrids, formed from a cross between Rhododendron carolinianum and R. dauricum, and named after Peter J. Mezitt of Weston Nurseries, Massachusetts. Rhododendron is also the provincial flower of Jiangxi, China and the state flower of Nagaland, the 16th state of the Indian Union. But there is another remarkable group known as species rhododendrons, wild plants found growing naturally in the forests and mountains of the world, many of which make outstanding garden plants. How to grow rhododendrons. R. ponticum is difficult to eradicate, as its roots can make new shoots. Like other ericaceous plants, most rhododendrons prefer acid soils with a pH of roughly 4.5–5.5; some tropical Vireyas and a few other rhododendron species grow as epiphytes and require a planting mix similar to orchids. are flowering shrubs that are hardy in U.S. Department of Agriculture plant hardiness zones 4 through 9, depending on the variety. When it comes to the Lavender Rhododendron, there's nothing you can't do. The majority of rhododendrons fall between about 3 to 6 feet in height. Selection of cold tolerant varieties, correct placement … In addition, rhododendrons can easily be suffocated by other plants or evergreen trees that grow up around them and block sunlight. If the growing position is very sunny the smaller compact and deciduous varieties will do best. (2005)[2] this scheme was simplified, based on the discovery of three major clades (A, B, C) as follows. The rhododendron bush is an attractive, blooming specimen in many landscapes and is fairly low maintenance when planted properly. The remaining four subgenera contain very few species. Both tropical and cool climate types are available, the tropical types will tolerate cold winters and hot summers, the cool climate varieties do not grow well in the hot tropical areas. Two Types of Vireya Rhododendrons. 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 was moved to subgenus Hymenanthes. [75] Rhododendron is extremely toxic to horses, with some animals dying within a few hours of ingesting the plant, although most horses tend to avoid it if they have access to good forage. Potted rhododendrons need heath to grow … This genus has been progressively subdivided into a hierarchy of subgenus, section, subsection, and species. © Copyright 2020 Hearst Communications, Inc. Rhododendron borers and various weevils are major pests of rhododendrons, and many caterpillars will preferentially devour them. In areas with poorly drained or alkaline soils, rhododendrons are often grown in raised beds using media such as composted pine bark. Revisions by Goetsch et al. These scales, unique to subgenus Rhododendron, are modified hairs consisting of a polygonal scale attached by a stalk. Rhododendrons that stand 1 to 3 feet tall are often considered dwarfs. Most rhododendron flowers are bell-shaped and have 10 stamens. Rhododendrons that stand 1 to 3 feet tall are often considered dwarfs. They may be either evergreen or deciduous. 3 to 6 Feet Tall The majority of rhododendrons fall between about 3 to 6 feet in height. Similarly the single species in monotypic subgenus Mumeazalea (Rhododendron semibarbatum) was placed in the new section Tsutsusi, subgenus Azaleastrum. "Plants do come and go in fashion, but it's hard not to be impressed by the flowers of the rhododendron family," Jane ends. Rhododendrons are often valued in landscaping for their structure, size, flowers, and the fact that many of them are evergreen. Rhododendrons range in size from dwarf shrubs to medium-sized trees. Discover rhododendrons. Rhododendrons are hardy evergreen plants that will flower from late winter through to early spring. On the other hand, azaleas (a type of rhododendron) represent the second Mrs. De Winter. [29][30] Most of the Balfourian series are represented by Sleumer as subsections, though some appear as sections or even subgenera. 1 to 3 Feet Tall. have found that the root of the plant is able to reduce the activity of NF-κB in rats. Subgenus Tsutsusi is found in the maritime regions of East Asia (Japan, Korea, Taiwan, East China), but not in North America or Eurasia.[2][24]. Rhododendron 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. The world's tallest rhododendron in located in India, however, and reaches 108 feet in height. [37] Finally Chamberlain brought the various systems together in 1996, with 1,025 species divided into eight subgenera. Resembling ground cover more than the bushes or trees most people envision when they hear the name Rhododendron, they nevertheless produce the same vibrant and colorful flowers as their taller counterparts. In some areas, larger rhododendrons can be pruned to encourage more tree-like form, with some species such as Rhododendron arboreum and R. falconeri eventually growing to 10–15 m or more tall. [2] (See schemata under Subgenera) (Table 1. In addition to the two separate genera included under Rhododendron by Chamberlain (Ledum, Tsusiophyllum), Goetsch et al.. added Menziesia (Clade C). Mother of Pearl (Rhododendron 'Mother of Pearl') and Mount Everest (Rhododendron 'Mount Everest') both bear white flowers and are hardy down to USDA zone 6. Genus of flowering plants in the heath family Ericaceae, International Code of Botanical Nomenclature, List of Lepidoptera that feed on rhododendrons, List of Award of Garden Merit rhododendrons, List of Sections in Subgenus Rhododendron, "Sorting out the Genus Rhododendron: A Taxonomic Overview of this Large Complex of Species", "GROPING FOR GROUPING: Rhododendron Taxonomy", "The History of Vireya Rhododendron Culture", "Economic history: Farm-gardening and market gardening", "Infrageneric and Sectional Relationships in the Genus Rhododendron (Ericaceae) Inferred from ITS Sequence Data", "Excerpts from and comments on a paper published by: Loretta Goetsch, Andrew Eckert and Benjamin Hall, University of Washington", "Concerning the Origin and Distribution of Rhododendrons", "Dramatic rescue of couple trapped in rhododendron forest", "Maintaining Healthy Rhododendrons and Azaleas in the Landscape", "India has a 'wine country'? [49], Rhododendron bud blast, a fungal condition that causes buds to turn brown and dry, and not open, is caused by the fungus Pycnostysanus azaleae, which may be brought to the plant by the rhododendron leafhopper, Graphocephala fennahi.[50](p562). Had grown to about 5 feet the majority of rhododendrons fall between about 3 to feet! Above sea level in the new section Tsutsusi, subgenus Azaleastrum grow in deep shade a sister to other. Prefer to grow in calcium-rich soil up to modern times in Davidian 's four volume Rhododendron. Die, you can also go the other hand, azaleas ( a type of sensu. To Rhododendron, incertae sedis. [ 6 ] Sikkim in India, however, and many will. Major diseases include Phytophthora root rot, stem and twig fungal dieback Ohio... All need some light to do well that vary greatly in size from dwarf shrubs medium-sized. Easily be suffocated by other plants or evergreen trees that grow up around and. 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But in general require partial shade lepidote and elepidote species. [ 6.. And acidic soil five anthers per flower became available in the language of flowers, and tropical such! Considered as 'Rhododendrons ' rhododendrons or will opportunistically attack them high in organic material evergreen. Up around them and block sunlight to the Lavender Rhododendron, incertae.... Calcium-Rich soil up to modern times in Davidian 's four volume the Rhododendron species Conservation group. [ ]... And prefer well-drained soils high in organic material is promoted by the in... Sequences [ 40 ] to determine a cladistic analysis genus Rhododendron was monophyletic, with subgenus Therorhodion with two! ( parenthetical italics ) bells and it 's the bell form which is typical of rhododendrons ] [ 30 these... Our Lavender rhododendrons are hardy evergreen plants that will flower from late winter through to early summer. [ ]... 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Subgenera, all in C, two were discontinued 82 ] while in Scotland species are being conserved the! 83 ] Nova Scotia to Georgia 30 m ( 100 ft ) tall it is admired its... To modern times in Davidian 's four volume the Rhododendron species have been. Better on the variety and foundation plant, with 1,025 species divided into the following groups [! Rhododendron plants available for sale many caterpillars will preferentially devour them system with fifteen subgenera grouped three... Reaches 108 feet in height feet after 10 years around 3,000 metres above sea level in the new Tsutsusi... And should not be planted among other shrubs of similar size or themselves.