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62-591: The American Rhododendron Society ( ARS ) 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

124-468: 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

186-431: 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

248-452: 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

310-455: A distinction can be made between a lower narrowed, stalk-like basal part referred to as the claw, and a wider distal part referred to as the blade (or limb). Often, the claw and blade are at an angle with one another. Wind-pollinated flowers often have small, dull petals and produce little or no scent. Some of these flowers will often have no petals at all. Flowers that depend on wind pollination will produce large amounts of pollen because most of

372-495: A floral cup ( hypanthium ) above the ovary, and from which the petals proper extend. A petal often consists of two parts: the upper broader part, similar to a leaf blade, also called the blade; and the lower narrower part, similar to a leaf petiole , called the claw , separated from each other at the limb . Claws are distinctly developed in petals of some flowers of the family Brassicaceae , such as Erysimum cheiri . The inception and further development of petals show

434-540: A great variety of patterns. Petals of different species of plants vary greatly in colour or colour pattern, both in visible light and in ultraviolet. Such patterns often function as guides to pollinators and are variously known as nectar guides , pollen guides, and floral guides. The genetics behind the formation of petals, in accordance with the ABC model of flower development , are that sepals, petals, stamens , and carpels are modified versions of each other. It appears that

496-540: 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

558-909: 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

620-419: 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

682-413: 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

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744-418: 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

806-437: A theory of the origin of elongated corollae and corolla tubes. A corolla of separate petals, without fusion of individual segments, is apopetalous . If the petals are free from one another in the corolla, the plant is polypetalous or choripetalous ; while if the petals are at least partially fused, it is gamopetalous or sympetalous . In the case of fused tepals, the term is syntepalous . The corolla in some plants forms

868-496: A tube. Petals can differ dramatically in different species. The number of petals in a flower may hold clues to a plant's classification. For example, flowers on eudicots (the largest group of dicots ) most frequently have four or five petals while flowers on monocots have three or six petals, although there are many exceptions to this rule. The petal whorl or corolla may be either radially or bilaterally symmetrical (see Symmetry in biology and Floral symmetry ). If all of

930-415: A variety of shapes acting to aid with the landing of the visiting insect and also influence the insect to brush against anthers and stigmas (parts of the flower). One such example of a flower is the pohutukawa ( Metrosideros excelsa ), which acts to regulate colour in a different way. The pohutukawa contains small petals also having bright large red clusters of stamens. Another attractive mechanism for flowers

992-472: 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,

1054-515: 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

1116-458: 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

1178-702: Is the use of scents which are highly attractive to humans. One such example is the rose. On the other hand, some flowers produce the smell of rotting meat and are attractive to insects such as flies. Darkness is another factor that flowers have adapted to as nighttime conditions limit vision and colour-perception. Fragrancy can be especially useful for flowers that are pollinated at night by moths and other flying insects. Flowers are also pollinated by birds and must be large and colourful to be visible against natural scenery. In New Zealand, such bird–pollinated native plants include: kowhai ( Sophora species), flax ( Phormium tenax ) and kaka beak ( Clianthus puniceus ). Flowers adapt

1240-733: 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

1302-591: 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

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1364-529: 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

1426-452: 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

1488-438: 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

1550-422: The pea family . In many plants of the aster family such as the sunflower, Helianthus annuus , the circumference of the flower head is composed of ray florets. Each ray floret is anatomically an individual flower with a single large petal. Florets in the centre of the disc typically have no or very reduced petals. In some plants such as Narcissus , the lower part of the petals or tepals are fused to form

1612-587: 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

1674-487: 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

1736-741: 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

1798-614: 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

1860-826: 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

1922-572: 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

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1984-432: The flower/petals are important in selecting the type of pollinators they need. For example, large petals and flowers will attract pollinators at a large distance or that are large themselves. Collectively, the scent, colour, and shape of petals all play a role in attracting/repelling specific pollinators and providing suitable conditions for pollinating. Some pollinators include insects, birds, bats, and wind. In some petals,

2046-561: 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

2108-425: 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 ,

2170-520: 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

2232-427: The mechanism on their petals to change colour in acting as a communicative mechanism for the bird to visit. An example is the tree fuchsia ( Fuchsia excorticata ), which are green when needing to be pollinated and turn red for the birds to stop coming and pollinating the flower. Flowers can be pollinated by short-tailed bats. An example of this is the dactylanthus ( Dactylanthus taylorii ). This plant has its home under

2294-411: The mechanisms to form petals evolved very few times (perhaps only once), rather than evolving repeatedly from stamens. Pollination is an important step in the sexual reproduction of higher plants. Pollen is produced by the male flower or by the male organs of hermaphroditic flowers. Pollen does not move on its own and thus requires wind or animal pollinators to disperse the pollen to the stigma of

2356-492: 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

2418-574: 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

2480-415: 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

2542-428: 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

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2604-514: The petals are essentially identical in size and shape, the flower is said to be regular or actinomorphic (meaning "ray-formed"). Many flowers are symmetrical in only one plane (i.e., symmetry is bilateral) and are termed irregular or zygomorphic (meaning "yoke-" or "pair-formed"). In irregular flowers, other floral parts may be modified from the regular form, but the petals show the greatest deviation from radial symmetry. Examples of zygomorphic flowers may be seen in orchids and members of

2666-531: The petals in aiding the pollinator towards the nectar. Pollinators have the ability to determine specific flowers they wish to pollinate. Using incentives, flowers draw pollinators and set up a mutual relation between each other in which case the pollinators will remember to always guard and pollinate these flowers (unless incentives are not consistently met and competition prevails). The petals could produce different scents to allure desirable pollinators or repel undesirable pollinators. Some flowers will also mimic

2728-399: The pollen scattered by the wind tends to not reach other flowers. Flowers have various regulatory mechanisms to attract insects. One such helpful mechanism is the use of colour guiding marks. Insects such as the bee or butterfly can see the ultraviolet marks which are contained on these flowers, acting as an attractive mechanism which is not visible towards the human eye. Many flowers contain

2790-475: 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

2852-519: 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

2914-420: The same or nearby flowers. However, pollinators are rather selective in determining the flowers they choose to pollinate. This develops competition between flowers and as a result flowers must provide incentives to appeal to pollinators (unless the flower self-pollinates or is involved in wind pollination). Petals play a major role in competing to attract pollinators. Henceforth pollination dispersal could occur and

2976-407: The scents produced by materials such as decaying meat, to attract pollinators to them. Various colour traits are used by different petals that could attract pollinators that have poor smelling abilities, or that only come out at certain parts of the day. Some flowers can change the colour of their petals as a signal to mutual pollinators to approach or keep away. Furthermore, the shape and size of

3038-442: The seed for later germination and planting. Petals Although petals are usually the most conspicuous parts of animal-pollinated flowers, wind-pollinated species, such as the grasses , either have very small petals or lack them entirely (apetalous). The collection of all petals in a flower is referred to as the corolla. The role of the corolla in plant evolution has been studied extensively since Charles Darwin postulated

3100-606: 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

3162-414: The survival of many species of flowers could prolong. Petals have various functions and purposes depending on the type of plant. In general, petals operate to protect some parts of the flower and attract/repel specific pollinators. This is where the positioning of the flower petals are located on the flower is the corolla e.g. the buttercup having shiny yellow flower petals which contain guidelines amongst

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3224-570: 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

3286-577: 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

3348-414: 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

3410-552: 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

3472-493: 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

3534-534: 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

3596-583: 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

3658-402: 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

3720-587: 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 )

3782-467: 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 )

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3844-411: 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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