The remaining small subgenus Therorhodion with its two species was left intact. (2005) this scheme was simplified, based on the discovery of three major clades (A, B, C) as follows. / Landscaping / Fall Planting, Pennsylvania, Perennials. , Rhododendrons are extensively hybridized in cultivation, and natural hybrids often occur in areas where species ranges overlap. The rootstock is able to grow in calcium-rich soil up to a pH of 7.5. 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. 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 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. Some hybrids have fragrant flowers—such as the Loderi hybrids, created by crossing Rhododendron fortunei and R.  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. , Rhododendrons are grown commercially in many areas for sale, and are occasionally collected in the wild, a practice now rare in most areas. They thrive in a moist, well-drained, humus-filled soil with a pH of 5.0 to 6.0, enriched with peat moss or leaf mold. Most species have brightly colored flowers which bloom from late winter through to early summer.. , 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. © Copyright 2020 Hearst Communications, Inc. Consequently, the taxonomy has been historically complex. , They have frequently been divided based on the presence or absence of scales on the abaxial (lower) leaf surface (lepidote or elepidote). 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 nested within clades A and B as monophyletic groups respectively. The shade-tolerant rosebay (Rhododendron maximum) grows wild from Nova Scotia to Georgia. 1 to 3 Feet Tall. The remaining four subgenera contain very few species. I was asked recently to do what I could to save a roughly 20-year-old Rhododendron, which had grown to about 5 feet. 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 the genus divided into eight sections. A number of insects either target rhododendrons or will opportunistically attack them. The truth is they need some light to do well.  Xiong et al. giganteum, reported to 30 m (100 ft) tall. We don't live there. 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. Many in this group flower early, such as Little Lou (Rhododendron 'Little Lou'), with yellow flowers and hardiness to USDA zone 6, or Cliff Garland (Rhododendron 'Cliff Garland'), which bears pink flowers and is hardy down to USDA zone 5.  (See schemata under Subgenera) (Table 1. By contrast subgenera Azaleastrum and Pentanthera were polyphyletic, while R. camtschaticum appeared as a sister to all other rhododendrons. Extensive information on rhododendron species: the history of their discovery, botanical details, toxicity, classification, cultural conditions, care for common problems, and suggestions for companion plants by Steve Henning. The key is the annual growth rate, up to 60cm per year for the most vigorous and less than 1cm for the slowest growing. (2005) and by Craven et al. These rhododendrons need ample room to grow and should not be planted on small lots or near sidewalks or driveways. There are alpine species with small flowers and small leaves, and tropical species such as section Vireya that often grow as epiphytes. Genus Menziesa (9 species) was also added to section Sciadorhodion. If you are new to growing Rhododendrons, this should be your first choice, since it is hardy in part-sun or shade, cold-tolerant and undemanding – a real beauty for easy growing and trouble-free gardening. In areas with poorly drained or alkaline soils, rhododendrons are often grown in raised beds using media such as composted pine bark. That system continued up to modern times in Davidian's four volume The Rhododendron Species..  In 2011 the two species of Diplarche were also added to Rhododendron, incertae sedis.. , 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. 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. Most have been bred for their flowers, but a few are of garden interest because of ornamental leaves and some for ornamental bark or stems. Information+photos of hybrids and species. Broadcast: Sat 5 Oct 2013, … At that time he considered the then known six species of Azalea that he had described earlier in 1735 in his Systema Naturae as a separate genus.. Records of the Rhododendron Society of America reside at the Albert and Shirley Small Special Collections Library at the University of Virginia. 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). Everything you need to know about choosing the right rhododendron for you. R. ponticum is difficult to eradicate, as its roots can make new shoots. Rhododendron is also the provincial flower of Jiangxi, China and the state flower of Nagaland, the 16th state of the Indian Union. Many gardeners think azaleas and rhododendrons prefer to grow in deep shade. griffithianum. , 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. The next two smaller subgenera (Pentanthera and Tsutsusi) represent the 'Azaleas'. These often-broadleaf evergreen plants boast large clusters of showy blooms at their growing tips in spring. Plant in spring or early fall. Rhododendrons have no ultimate size, they can carry on growing indefinitely.  Finally Chamberlain brought the various systems together in 1996, with 1,025 species divided into eight subgenera. 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. Of the three minor subgenera, all in C, two were discontinued. Rhododendrons have fibrous roots and prefer well-drained soils high in organic material. The rhododendron bush is an attractive, blooming specimen in many landscapes and is fairly low maintenance when planted properly. 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. They may be either evergreen or deciduous. Soil preparation is best accomplished in autumn before planting the rhododendron in spring. People have been known to become ill from eating honey made by bees feeding on rhododendron and azalea flowers. They can get real big. Pink Rhododendron (Rhododendron campanulatum) is the State Flower of Himachal Pradesh, India. Where to Plant Rhododendrons Traditional rhododendrons thrive in filtered sunlight and acidic soil. 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. and R. maximum). :51 The flower, fresh or dried, is added to fish curry in the belief that it will soften the bones. Choose heat-tolerant kinds. Yes, it does! Of the first two of these, the species are predominantly found in the area of the Himalayas and Southwest China (Sino-Himalayan Region). (2008) shown in (parenthetical italics). 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. , Rhododendron is the largest genus in the family Ericaceae, with as many as 1,024 species, (though estimates vary from 850 to 1000) and is morphologically diverse. 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. Evergreen rhododendrons - large group of evergreen shrubs that vary greatly in size.  In 1986 Philipson & Philipson raised two sections of subgenus Aleastrum (Mumeazalea, Candidastrum) to subgenera, while reducing genus Therorhodion to a subgenus of Rhododendron. 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. Selection of cold tolerant varieties, correct placement … Rhododendron arboreum is also the state tree of the state of Uttarakhand, India. R. ponticum is the state flower of Indian-administered Kashmir and Pakistan-controlled Kashmir. They can be planted by themselves but are also attractive when planted in groups. Proper soil preparation is also necessary for the health of this acid loving plant. 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. have found that the root of the plant is able to reduce the activity of NF-κB in rats.  Bentham and Hooker used a similar scheme, but called the divisions "Series". Difference Between Mountain Laurel & Rhododendrons, American Rhododendron Plant Society Registry, American Rhododendron Society Massachusetts Chapter, Missouri Botanical Garden: Rhododendron (PJM Group), Virginia Tech: Journal American Rhododendron Society. 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. The world's most glorious rhododendrons grow in Seattle, Ireland, England, New Zealand, and other places in the Goldilocks zone where it's not too hot, not too cold, but just right. Rhododendrons that stand 1 to 3 feet tall are often considered dwarfs. ), Subsequent research has supported the revision by Goetsch, although has largely concentrated on further defining the phylogeny within the subdivisions. :540–541 They can self-propagate by sending up shoots from the roots.  Chamberlain and Rae moved the monotypic section Tsusiopsis together with the monotypic genus Tsusiophyllum into section Tsutsusi, while Kron & Judd reduced genus Ledum to a subsection of section Rhododendron. Rhododendrons are hardy evergreen plants that will flower from late winter through to early spring. Pink-flowered varieties include Furnival's Daughter (Rhododendron 'Furnival's Daughter') and Van (Rhododendron 'Van'), which are hardy down to USDA zone 6.  It is an introduced species, spreading in woodland areas and replacing the natural understory. On one extreme, there are species in China that barely reach 2 inches in height, yet China also has species that reach 80 feet or more. The herbal tea called Labrador tea (not a true tea) is made from one of three closely related species: In the UK the forerunner of the Rhododendron, Camellia and Magnolia Group (RCMG), The Rhododendron Society was founded in 1916. A new calcium-tolerant stock of rhododendrons (trademarked as 'Inkarho') has been exhibited at the RHS Chelsea Flower Show in London (2011). Twenty-four species of rhododendron are native to North America. Amongst the Zomi tribes in India and Myanmar, "Rhododendrons" called "Ngeisok" is used in a poetic manner to signify a lady.  Most of the Balfourian series are represented by Sleumer as subsections, though some appear as sections or even subgenera. Dig a hole as deep as the root ball and 2 times as wide. After they bloom and the flowers die, you can prune them back a little each year. Older ranks such as Series (groups of species) are no longer used but may be found in the literature, but the American Rhododendron Society still uses a similar device, called Alliances, 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 the Solomon Islands. Two Types of Vireya Rhododendrons. The pot’s size is also important, it shouldn’t be too big. Larger commercial growers often ship long distances; in the United States, most of them are on the west coast (Oregon, Washington state and California). The small polyphyletic subgenera Pentanthera and Azaleastrum were divided between two clades. Rhododendrons are a diverse group of plants that also include both evergreen and deciduous azaleas. ’Scarlet Wonder’ is a red-flowered dwarf variety with a maximum height and spread of just 2 to 3 feet, perfect for small spaces. 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