Barry Davidson, Lyn Craven, Bob Malone, Rodger Davidson, Jack Wilson, Roger SpencerGreek rhodo—rose, dendron—tree.

Greek rhodo—rose, dendron—tree.

Evergreen and deciduous shrubs, occasionally small trees or epiphytes. Leaves simple, alternate (but often gathered into false whorls at the ends of the branches), mostly entire with the margins often rolled under, short-stalked. Flowers mostly in terminal clusters (initially enclosed in bud scales that are soon shed), occasionally axillary or solitary, mostly June-Nov. Sepals mostly 5 parted or same number as petals, often small. Flowers funnel-like, cam­panulate to tubular or rotate often 5-lobed or with 2 lips, sometimes with blotches of a different colour on the upper petals. Occasionally flowers become doubled, especially in the Kurumes. Stamens mostly 10, rarely 5; anthers without awns and opening by a terminal pore. Ovary superior with 5-10 chambers, each with many seeds that are sometimes winged with tails at one or both ends. Fruit a capsule splitting from the top.

This account is arranged according to the major groups accepted by nurserymen and growers but through the text indications are also given of the current botanical classification. Readers should take care when extrapolating from books written overseas as Australia has its own cultural requirements, the evergreen groups, for example, being grown quite easily outside.

Historical background: Possibly the first introduction of Rhododendron to Australia was to Alexander Macleay's Elizabeth Bay, New South Wales, in 1826 or 1836. An outline of the history of introduction of rhododendrons to Victoria is given in Wilson (1970) and Hutton (1985). Rhododendron ponticum appears to be one of the most popular early introductions although show prizes were not awarded to rhododendrons until the 1870s. In Victoria important importing nurseries were Thomas Lang and Co. in the cooler Ballarat climate, also the nurseries of R.U. Nicholls and G. Smith. Lang especially imported hundreds of plants in the 1860s and embarked on his own breeding program. A little later, in the late 1870s to the 1880s, enthusiasm spread to Mount Macedon and Melbourne and Taylor and Sangster's nursery became prominent towards the turn of the century. The Dandenongs later became the centre for growing rhododendrons where nurseryman William Chandler and his son Bert and grandson John are notable, in­heriting much of the stock used by the earlier nurseries. A history of rhododendron growing in Tasmania is given in Sullivan (1990).

Seed and layers. Cultivars are raised primarily by tip cuttings and occasionally by grafting. For enthusiasts the seed bank of the Australian Rhododendron Society can be accessed and includes seed from the American Rhododendron Society.

Capsular fruits with many seeds. Flowers funnel-like or campanulate, never urn-shaped.

VIC: In the Dandenongs there are several collections-The National Rhododendron Garden, Olinda (see The Rhododendron 25(1):4-9) and 'Pirianda', a property now maintained by Parks Victoria; other smaller collections can be seen at the Alfred Nicholas Memorial Garden, Pallants' Hill, and dwarf rhododendrons in the collection of Lesley and Graham Eaton. SA: Mt Lofty Botanic Garden (c. 500 species in 1994). NSW: Blue Mountains Botanic Garden Mount Tomah and Royal Botanic Garden Sydney (Vireyas); The Campbell Rhododendron Gardens, Blackheath (see The Rhododendron 27(2):37-39); Illawarra Rhododendron Garden at Mt Pleasant near Wollongong (see The Rhododendron 32:39-40 (1992) –1500 vireya plants established in 1987). TAS: W.A.G. Walker Rhododendron Reserve, Lalla; Emu Valley Rhododendron Garden near Burnie (see The Rhododendron 26(4):72-74), Lapoinya Rhododendron Gardens; private collections of Fay Marsland in a park-like area behind her house in Oakleigh Ave, Taroona, also the collections of Barry Davidson at Claremont (with a wide range of latest imports to Australia) and Peter Phipps of Margate. NZ: Pukeiti (Rhododendron Trust) near New Plymouth.

Hybridising in Australia: Interest in hybridising developed in the 1950s with both amateurs and commercial nurserymen aiming to produce rhododendrons better suited to Australian conditions. Parent plants were initially imported from England and Holland, followed by hybrids developed on the West Coast of the USA. The leader in this local development was Victor Boulter of Boulter's Olinda Nursery, who began hybridising in 1949 and made his first registration in 1961. Many of his cultivars were early season flowering, a valuable quality in Australia. They include: 'Abbey Boulter', 'Apricot Sun', 'August Moon', 'Beaut One', 'Boulter's Cream', 'Canolle Gleam', 'China Doll', 'Colehurst', 'Corinne Boulter', 'Debbie Thomson', 'Denise', 'Desert Star', 'Desert Sun', 'Early Days', 'Edith Boulter', 'Faith Henty', 'Grace Patterson', 'Heatherdale', 'Jeanette Clarke', 'Joan Bye', 'Kalimna', 'Lyn Boulter', 'Margaret Mack', 'Mauve Bouquet', 'Melba', 'Mundai', 'Murrabra', 'Natalie Murray', 'Noele Boulter', 'Noila', 'Noorook', 'Olinda Ruby', 'Purple Opal', 'Rhonda', 'Robyn', 'Boulter's Rosalea', 'Saki', 'Shirley Scott', 'Tulla', 'Victor Boulter', 'Winning Post', 'Winter Beauty', 'You Beaut'. Dwarf varieties: 'Candle Gleam', 'Heather', 'Pink Gem'. Many other breeders followed, but the outstanding one has been Karel Van de Ven of Olinda Nurseries who has been producing beautiful new hybrids for over 20 years (see Withers, 1986).

In view of the large number of species, cultivars and hybrids available, together with the difficult characters involved (presence and structure of small scales; presence and structure of hairs; seed structure; stamen number and hairiness and other characters difficult to observe), it has been decided that a botanical key would in all probability not assist the reader greatly and may, in fact, lead to incorrect conclusions. However, for those keen to attempt identification by this method there is a key provided in The New Royal Horticultural Society Dictionary of Gardening Vol. 4 pp. 36-54 (Huxley, 1992). Horticulturally the situation is, of course, complicated by the range of available hybrids and cultivars. There are now over 20 000 cultivars registered by the Royal Horticultural Society at Wisley, England, which is the International Registration Authority for the genus (see Appendix 1). Australia has approximately 1500 commercially available cultivars, of which only a small selection can be considered here. The Australian Registrar is Mr Graeme Eaton, 1386 Mt Dandenong Tourist Road, Mt Dandenong, Victoria 3767.

A widespread genus of about 900 species of mostly northern temperate regions chiefly Himalaya, SE Asia and Malesia with possibly 2 species extending into northern Australia. There are centres of distribution in SW China and Papua New Guinea.

The literature on rhododendrons is vast. References cited here have been restricted to major synoptic accounts and botanical revisions. General accounts: Leach (1962), Bean (1976c), van Gelderen & van Hoey Smith (1992, colour illustrations), Smith (1989, vireyas). Bibliographies: Schwartz (1975), Bean (1976c). Cultivars and Hybrids: Kraxberger (1980), Cox & Cox (1988), Sally & Greer (1992); see also in the following periodicals section. Species: Cox (1979), Cox (1985), Davidian (1982, 1989, 1992, 1995). The Rhododendron Handbook-Rhododendron Species in Cultivation Leslie, 1980, to be revised soon). Azaleas: Galle (1987), Bryant (1991). Periodicals: The Rhododendron Year Book, R.H.S., London, 1946-55. Rhododendron and Camellia Year Book, R.H.S., London 1956-71. Rhododendrons with Camellias and Magnolias. R.H.S. London. 1973 onward annually. Quarterly Journal of the American Rhododendron Society, about 1946 onwards. The Azalean, a quarterly publication of the Azalea Society of America, 1979 onward. Descriptions and names of rhododendron cultivars accepted for registration were included in this publication until 1987, after which they have been listed in a special supplement. In Australia there is The Rhododendron, a quarterly journal of the Australian Rhododendron Society 1959-90 which became an annual publication from 1990 onward.

The classification of the genus Rhododendron is complex. The Royal Botanic Gardens, Edinburgh has traditionally been closely associated with the taxonomy of the genus (most notably the system of Balfour at the turn of the century which is still used by some rhododendron growers) and has maintained a large living collection. Perhaps the most impressive early classification scheme is that of Sleumer (1949). In recent years the genus has been completely revised at Edinburgh using modern criteria and techniques to produce a more natural system (reflecting evolutionary relationships) than the several artificial preceding systems that were developed in a rather ad hoc fashion as new species flooded in for description in the 19th and early 20th centuries.

There is little point in presenting here the contemporary arrangement of species into 8 subgenera with numerous sections and subsections: the interested reader can consult a preliminary synopsis in Cullen and Chamberlain (1978), now superseded by the literature below. Suffice it to say that the 2 largest subgenera are subgenus Rhododendron characterised by small scales on various parts (the lepidote or scaly rhododendrons), and subgenus Hymenanthes which lacks scales (elepidote rhododendrons). Hybrids are not easily formed between species of the 2 subgenera although they do occur freely within each subgenus, making the subgeneric distinction of both taxonomic and practical importance. The scales can just be seen with the naked eye and with practice other characters can be discerned so that the 2 subgenera may be distinguished at a distance.

The following taxonomic works may be consulted for details of classification: a revision of section Vireya in the subgenus Rhododendron in Sleumer (1966) with modifications to this system published by Argent et al. (1988); Rhododendron section Lapponicum in Philipson & Philipson (1975); subgenus Rhododendron sections Rhododendron and Pogonanthum in Cullen (1980); subgenus Hymenanthes in Chamberlain (1982); subgenera Azaleastrum, Mumeazalea, Candidastrum and Theorhodion in Philipson & Philipson (1986); subgenus Tsutsusi in Chamberlain & Rae (1990); Rhododendron section Pentanthera in Kron (1993); subgenus Pentanthera sections Sciadorhodion, Rhodora and Viscidula in Judd & Kron (1995).

General introduction: Rhododendron is an extremely important genus in northern temperate horticulture. The requirement of many of the broad-leaf rhododendrons for cool, moist, rich and acidic soils coupled with mild summers, humidity and cool winters restricts the better Australian collections to the cool-climate hill districts of South Australia, Victoria, New South Wales and especially Tasmania. However, Australia has taken advantage of its climate to explore the potential of some of the evergreen azalea groups and lead the world in breeding the montane-tropical Vireya rhododendrons.

The rhododendrons, both species and cultivars, are here divided into 4 groups for convenience: tall rhododendrons-which grow over 2 m in 10 years with leaves more or less in proportion to the size, although with large flower trusses; medium rhododendrons-growing 1.5-2 m tall; low rhododendrons up to 0.5 m-1.25 m tall; and dwarf rhododendrons to 0.5 m tall with very small leaves and flower trusses.

These last 4 groups are presented here within a botanical classification so that a few representatives can be mentioned from each part of the classification. Descriptions of cultivars have been largely extracted from Cox & Cox (1988). The genus Rhododendron now also includes what was formerly the genus Azalea which is now part of the subgenus Tsutsusi, comprising 66 evergreen azalea species in section Tsutsusi and 30 deciduous azaleas in sections Brachycalyx and subgenus Pentanthera section Pentanthera. The name 'azalea' is retained by nurserymen as a convenient term for plants which have small to medium sized funnel-shaped flowers (usually broad) with 5-10 stamens, and leaves with hairs closely pressed to the surface. The evergreen azaleas are generally smaller than the deciduous ones and both contrast with the tall, broad-leaf tree rhododendrons of the subsections Grandia and Falconera in the subgenus Hymenanthes, section Ponticum: these have large leaves, are over 6 m tall when mature and bear huge trusses of large flowers.

Vireyas, which are mainly tropical and belong to the section Vireya of the subgenus Rhododendron, have waxy trumpet-shaped or tubular flowers and may bloom in any season, but they are never spotted or found in blues or mauves, their seeds are winged.

 

Broad-leaf Rhododendrons: The Broad-leaf rhododendrons are in the subsections Falconera and Grandia of the subgenus Hymenanthes; they grow naturally from E Nepal through Bhutan into the western provinces of China and south into upper Burma as a high understorey or upper storey of the forest. The differences between the subsections are not always clear but their most obvious feature is the extremely large ornamental leaves, rarely less than 25 cm long (in established specimens) and covered with fine hairs called the tomentum. The flowers, which are rarely produced on plants less than 8 years old, are 7-10 lobed and bell-shaped with 12-20 stamens. As woodland plants they require a moist soil and some shade with protection from extremes of heat and cold. A selection of the most spectacular and popular species is described, growers produce these from seed or grafting. Hybrids between species of this group are fairly rare and generally of no great merit. However, worthwhile cultivars include 'Fortune' with bright yellow flowers and 'Elsae' with ivory white flowers having crimson basal blotches. Australian enthusiasts are breeding species to produce a greater flower colour range on smaller plants that bloom early and survive well in our climate.

 

Tall Rhododendrons: This group is one of practical convenience selected here to consist of plants which, after 10 years will grow over 2 m tall and are not azaleas, vireyas or big-leaf rhododendrons. Plants over 2 m tall tend to spread under their own weight and height increase is slow. Most of this group are from the Himalaya although a few range south into Burma and across to Vietnam. Only 3 of the species listed below are out of this range: R. maximum and R. catawbiense from E and W coasts of the USA and R. ponticum from around Turkey and the southern Iberian Peninsula. Plants in this group need moisture and they tolerate more sunlight than the broad-leaf rhododendrons. Soil iron deficiencies in pH.s over 5.5-6 may be overcome using chelates at first and iron sulphate long-term. Propagation is by cuttings, rarely by grafting, layers will form fairly readily in the garden. Plants are presented within their botanical classification to indicate species that are available within their formal groupings.

Subgenus hymenanthes (elepidotes)

Subsection Arborea. R. arboreum Sm. Flowers blood red (rarely white) and cup-shaped. Subspecies include: cinnamomeum (Wall.) Tagg with white flowers and a thick layer of hair on lower leaf surface: 'Sir Charles Lemon' is a selection; delavayi Franch. and zeylanicum (Booth) Tagg 'Noyo Chief' with pale red flowers and shiny leaves is a selection. R. niveum Hook. has pale purple flowers.

Subsection Barbata. R. barbatum G. Don Flowers bright red.

Subsection Campanulata. R. campanulatum D. Don Flowers white to pale lilac.

Subsection Fortunea. R. calophytum Franch. Flowers pale pink with a deep basal blotch. R. decorum Franch. Flowers white, sometimes pinked pale green or pink. subsp. diaprepes Balf. f. & W.W. Sm. Flowers late, white. R. fortunei Lindl. Flowers pink, fragrant; also subsp. discolor. R. griffithianum Wight Flowers pale pink to white. R. hemsleyanum E.H. Wilson Flowers white. R. sutchuenense Franch. Flowers pale pink to lilac.

Subsection Irrorata. R. irroratum Franch. Flowers pale, heavily spotted. Subsection Lactea. R. lacteum Franch. Flowers pale yellow.

Subsection Pontica. R. catawbiense Michx. Flowers lilac-pink. R. maximum L. Flowers white to pink. R. ponticum L. Flowers mauve. There are improved selections.

Subsection Thomsonia. R. thomsonii Hook. Flowers red, leaves rounded.

Subgenus Rhododendron (lepidotes)

Section Rhododendron

Subsection Cinnabarina. R. cinnabarinum Hook. Flowers of long tubular red or orange bells. Leaves waxy blue. A complex group.

Subsection Maddenia. R. lindleyi T. Moore Flowers white tinged pink, strongly scented. R. nuttallii Nutt. Flowers white, strongly scented.

Subsection Scabrifolia. R. spinuliferum Franch. Flowers facing upwards, red with prominent yellow stamens, sometimes tipped black.

 

Medium Rhododendrons:

Subgenus Hymenanthes (elepidotes)

Section Hymenanthes

Subsection Campylocarpa. R. campylocarpum Hook. Flowers pale yellow. R. souliei Franch. Flowers creamy yellow to pink. R. wardii W.W. Sm. Flowers pale yellow.

Subsection Fulva. R. fulvum Balf. f. & W.W. Sm. Flowers pale to deep pink, leaves with brown hair.

Subsection Maculifera. R. morii Hayata Flowers white, clear or spotted.

Subsection Parishia. R. elliottii Watt Flowers red.

Subsection Taliensia. R. bureavii Franch. Flowers whitish with a thick layer of hair on the leaf undersurface.

Subgenus Rhododendron

Section Rhododendron

Subsection Maddenia. R. ciliicalyx Franch. Flowers white or pale pink. R. dalhousiae Hook. var. rhabdotum (Balf. f. & Cooper.) Cullen Flowers pale yellow. R. formosum Wall. Flowers white to pink, fragrant. R. johnstoneanum Hutch. Flowers variable, cream to yellow. Double forms exist e.g. ‘Double Diamond’. R. maddenii Hook. Flowers white to pink. R. megacalyx Balf. f. & Kingdon-Ward Flowers white with a large calyx. R. scopulorum Hutch. Flowers pink. R. veitchianum Hook. Flowers early, white.

Subsection Rhodorastra. R. mucronulatum Turcz. Deciduous, the pink flowers appearing before the leaves.

Subsection Triflora. R. ambiguum Hemsl. Flowers pale greenish yellow. R. augustinii Hemsl. Extremely variable with many cultivars. ‘Tower Court’ has blue flowers. R. concinnum Hemsl. Flowers white to purple or red. R. davidsonianum Rehder & E.H. Wilson Flowers mauve or pink. Pink cultivars include: ‘Caerhays Castle’ and ‘Ruth Lyons’. R. lutescens Franch. Flowers pale yellow. R. oreotrephes W.W. Sm. Mauve or pink flowers, leaves waxy blue. R. yunnanense Franch. Flowers white to pink.

 

Low Rhododendrons: The low rhododendrons tolerate more sun than the taller rhododendrons.

Subgenus Hymenanthes

Section Hymenanthes.

Subsection Campylocarpa. R. campylocarpum Hook. subsp. caloxanthum (Balf. f. & Farrer) D.F. Chamb. Flowers pale yellow.

Subsection Fortunea. R. orbiculare Decne. Flowers pale pink, leaves rounded.

Subsection Genestieria. R. genestierianum Forrest Flowers small, reddish purple, leaves waxy blue below.

Subsection Griersoniana. R. griersonianum Balf. f. & Forrest Flowers pinkish.

Subsection Irrorata. R. aberconwayi Cowan Flowers white to pink.

Subsection Maculifera. R. pachysanthum Hayata Flowers white to pink, leaves blue-green with dense hair.

Subsection Neriiflora. R. dichroanthum Diels Flowers mostly orange, sometimes suffused pink. R. haematodes Franch. subsp. haematodes Flowers crimson. R. mallotum Balf. f. & Kingdon-Ward Flowers crimson. R. sanguineum Franch. Flowers crimson. R. forrestii Diels Flowers crimson. R. neriiflorum Franch. Flowers crimson.

Subsection Pontica. R. degronianum Carrière Flowers rose-pink, white or red-dotted.

Subsection Taliensia. R. adenogynum Diels Flowers white, tinged with pink or spotted. R. roxieanum Forr. var. oreonastes (Balf. f. & Forrest) T.L. Ming Flowers white to white flushed pink or dotted.

Subsection Williamsiana. R. williamsianum Rehder & E.H. Wilson Flowers pinkish red.

Section Rhododendron

Subsection Boothia. R. chrysodorum Hutch. Flowers yellow, leaves shiny. R. leucaspis Tagg Flowers white with brown stamens.

Subsection Edgeworthia. R. edgeworthii Hook. Flowers white, fragrant.

Subsection Glauca. R. luteiflorum Davidian Flowers small, pale yellow, leaves waxy blue below.

Subsection Lapponica. R. flavidum Franch. Flowers pale yellow, leaves small. R. hippophaeoides Balf. f. & W.W. Sm. Flowers pale purple. R. intricatum Franch. Flowers purple, leaves small. R. russatum Balf. f. & Forrest Flowers purplish blue, leaves small. R. websterianum Rehder & E.H. Wilson Flowers pale purple, leaves small, waxy blue.

Subsection Maddenia. R. burmanicum Hutch. Flowers yellow. R. ciliatum Hook. Flowers white to pale pink. R. fletcherianum Davidian Flowers pale yellow. R. lyi Lév. Flowers white blotched yellow.

Subsection Moupinensia. R. moupinense Franch. Flowers white to pink, rarely reddish.

Subsection Tephropepla. R. auritum Tagg. Flowers straw yellow. R. hanceanum Hemsl. Flowers creamy white (dwarf forms occur). R. tephropeplum Balf. f. & Farrer Flowers from pink to reddish purple. R. xanthostephanum Merr. Flowers yellow.

Subsection Trichoclada. R. mekongense Franch. Deciduous, flowers pale yellow tinged with red.

Subsection Triflora. R. keiskei Miq. Flowers pale yellow (dwarf forms occur).

Subsection Virgata. R. virgatum Hook. Flowers white to dark pink.

 

Dwarf Rhododendrons: Dwarf rhododendrons generally grow naturally at high altitude in the Himalaya where there is snow for several months of the year. They are mainly lepidotes and make good specimens for the rock garden and for alpine plant specialists. The leaves are generally relatively small.

Subgenus Rhododendron

Section Rhododendron

Subsection Campylogyna. R. campylogynum Franch. Flower colour variable from white to salmon-pink to blackish purple.

Subsection Lapponica. R. complexum Balf. f. & W.W. Sm. Flowers pale to deep purple.

Subsection Lepidota. R. lepidotum G. Don Flowers deep pink to purple

Subsection Maddenia. R. valentinianum Hutch. Flowers butter-yellow.

Subsection Rhodorastra. R. calostrotum Balf. f. & Kingdon-Ward Flowers crimson. There are various forms of this species.

Subsection Scabrifolia. R. racemosum Franch. Flowers various shades of pink.

Subsection Ludlowia. R. ludlowii Cowan Flowers pale yellow spotted brownish red. R. pemakoense Kingdon-Ward Flowers pink or purplish.

Subsection Pogonantha. R. sargentianum Rehder & E.H. Wilson Flowers small, creamy white to yellow.

Subsection Therorhodion. R. camtschaticum Pall. Flowers deep purplish red on a small plant to 15 cm high.

 

Vireyas (Subgenus Rhododendron section Vireya): The tropical section Vireya contains about 280 species (approximately one third of the species in the genus Rhododendron) most coming from the cooler montane mist forests of SE Asia, chiefly New Guinea, Borneo and the Philippines (2 species occur in N Australia); some grow above the tree line where they are subject to night frosts. In the northern hemisphere vireyas require warmth and are generally grown as glasshouse plants but in Australia their popularity is due partly, it seems, to the fact that they can be grown outside, and partly for the appeal of growing plants that grow in relatively close geographic proximity to Australia—most species are from the Malesian region and have been swelled, since the 1960s, by collections from Papua New Guinea. They are characterised by their rather lanky habit but may be pruned to form compact bushes. In nature some species are epiphytic on trees, others grow on rock. The flowers are extremely variable in form but mostly richly coloured, waxy and tubular to cup- and funnel-shaped. Technical botanical characters distinguishing the group include seeds that have tails at each end, and distinctive scales on the leaves.

A history of the introduction of vireya rhododendron species to Australia is given by Dr R.M. Withers in The Rhododendron 31:3–15 (1991), and Lyn Craven (1973) has writtten a history of their introduction and cultivation and assembled a list of species that are or have been cultivated in Australia (Craven, 1993). A botanical account of species is given in Sleumer (1966).

Australian commercial interest in vireyas began in the mid 1970s. Certainly Graham and Wendy Snell were among the first, in co-operation with the Australian Rhododendron Society, to explore both species and the early available hybrids—at first in their Victorian Nursery ‘Shrublands’, then in 1988 at Maleny, Queensland as ‘The Vireya Venue’. Much early breeding was carried out in Melbourne by Dr John Rouse and Tom Lelliott. Brian Clancy has been growing Vireyas at Bentleigh, Victoria since 1962 and has produced many fine hybrids. He is breaking new ground with his latest R. rubineiflorum hybrids which are floriferous compact hardy dwarfs. In New Zealand Os Blumhart is an active breeder producing exciting new cultivars.

A compendium of vireya species and hybrids is available from Clover Springs Computer Services, P.O. Box 500, Brentford Square, 3131. Edition 2 was produced in hard copy in 1993 (CSCS, 21 Squire Terrace, Colts Neck, New Jersey 07722, USA).

A wide range of vireya species is now grown and the following are among those more widely available and often used for breeding. R. aurigeranum, R. jasminiflorum, R. konorii, R. laetum, R. leucogigas, R. lochiae, R. loranthiflorum, R. macgregoriae and R. zoelleri.

 

Australian-raised Vireya cultivars (list comipiled by the Australian Rhododendron Society Southern Tasmanian Branch) to 30 June 1994:  'Ada Verspeek', 'Aida's March', 'Alisa Nicole', 'Anatta Gold', 'Angi Gita', 'Arthur's Choice', 'Auburn Beauty', 'Australia II', 'Autumn Berry Wine', 'Barbara Crouch', 'Benjamin Macdonald', 'Blonde Bombshell', 'Blonde Venus', 'Bob's Crowning Glory', 'Bold Janus', 'Breathless', 'Bright Lights', 'Brunswick Green', 'Bulolo Gold', 'Buttermilk', 'Cake and Ale', 'Carillon Bells', 'Catherine the Great', 'Celebration', 'Channon Marie', 'Charming Valentino', 'Chayya', 'Cheeky Mandarine', 'Cherry Harmony', 'Choc Orange', 'Choirs of Angels', 'Christmas Past', 'Christmas Present', 'Christopher Borch', 'Christopher John', 'Cinnamon Pink', 'Claire Crouch', 'Claire Rouse', 'Clarion Firm', 'Concerto for Brass', 'Coral Flare', 'Craig Faragher', 'Crimson Lightning', 'Crimson Scallywag', 'Crinolette', 'Crisp Deroy', 'Cybelle Barbour', 'David Crouch', 'Diamond Jubilee', 'Doll Tsarsheet', 'Doctor Hermann Sleumer', 'Dressed to Kill', 'Duchess Satin', 'Dulcie Lelliott', 'Eastern Zanzibar', 'Elation', 'Elizabeth Crouch', 'Esprit-de-Joie', 'Eureka Gold', 'Faberge's Egg', 'Ferdinand von Mueller', 'Finnegan's Rainbow', 'Fireplum', 'Flaming Ball', 'Fuchsia Lady', 'Fyrglo', 'Gardenia Odyssey', 'Gentle Jenny', 'Glen Borch', 'Gossamer White', 'Great Scent-sation', 'Green with Envy', 'Hari's Choice', 'Happy Times', 'Helen's Laughter', 'Hendre', 'High Country Wedding', 'Highland Arabesque', 'Highland Fair', 'Highland Peter Pan', 'Highland White Jade', 'Hilda Margaret Crouch', 'Hip-Hip-Hurrah', 'Hosanna', 'Hotel on Mayfair', 'Iced Primrose', 'Innuendo', 'Island Sunset', 'Janelle Marie', 'Jeremy Funder', 'Joly Roger', 'Josephine Gordon', 'Kaleidascope', 'Kay Catchlove', 'Kiandra', 'La-De-Da', 'Lady Clare', 'Lana's Gold', 'Lemon Minuet', 'Liberty Bar', 'Little Nell', 'Little One', 'Little Pinkie', 'Littlest Angel', 'Lochmin', 'Lolly Willows', 'Lovey', 'Lucifer's Blush', 'Lucifer's Marjiam', 'Melbourne Cup', 'Mistress Sue', 'Mrs Elizabeth Miller', 'Nancy Cutten', 'Niugini Firebird', 'Orange Harmony', 'Orange Wax', 'Oriental Orange', 'Our Marcia', 'Overflow', 'Pacific Moonrise', 'Pacific Shower', 'Pacific Sundown', 'Patrizia Del Roma', 'Pedance', 'Pendragon', 'Penny Whistle', 'Penrice', 'Penrose', 'Personality', 'Pindi Peach', 'Pindi Pearl', 'Pink Feathers', 'Pink Lightning', 'Pink Pazazz', 'Pink Sally', 'Platinum Blonde', 'Poet Laureate', 'Popcorn', 'Pretty Cotton Candy', 'Ratafia', 'Red Rooster', 'Hunstein's Secret', 'Rich Amber', 'Robert Withers', 'Rogue Red', 'Rouseabout', 'Ruby Bells', 'Scarlet Beauty', 'Scotchburn White', 'Shantung Pink', 'Shantung Rose', 'St Valentine', 'Stanton's Glory', 'Star Shower', 'Sunny', 'Sunset Fantasy', 'Sweet Amanda', 'Sweet Beatrice', 'Sweet Cherubim', 'Sweet Mac', 'Sweet Rosalie', 'Sweet Seraphim', 'Sweet Wendy', 'Thief of Hearts', 'Tiffany Rose', 'Tinkerbelle's Flight', 'Tom Lelliott'. 'Tops o Kew', 'Torrid Affair', 'Tosca's Kiss', 'Tropic Fanfare', 'Tropic Fanfare', 'Tropic Summer', 'Tropic Tango', 'Vanilla Cream', 'Veronica Maureen', 'Wattle Bird', 'Wee Willie Winkie', 'White Giant', 'White Rum', 'Wild Redhead', 'Zoe Elloise'

 

Azaleas (Subgenus Tsutsusi sections Tsutsusi and Brachycalyx  and Subgenus Pentanthera Section Pentanthera): Azaleas are botanically part of the genus Rhododendron but as they form a distinctive and convenient horticultural grouping they are likely to retain the traditional (and once botanical) common name azalea. They can be divided into two kinds that, in general, do not cross-breed – the deciduous and evergreen groups. Azalea breeders have developed five variations on the usual single flower form: semi-double in which modified stamens form what appears to be a central cluster of contorted petals; double in which the modified stamens form a central contorted cluster that looks like another set of petals; hose-in-hose where the sepals are petal-like and alternate behind the petals in a second whorl; semi-double hose-in-hose and double hose-in-hose combine the features already described. Spider-form flowers are also sometimes grown. Readers requiring a detailed and authoritative account of azaleas should consult the book by Galle (1987).

 

Deciduous Azaleas: These originate from Asia, S Europe and North America and can be divided into several more or less distinct groups

Ghent Azaleas (derived from American and European species) Oldest hybrid deciduous azalea group derived from small-flowered, long-tubed eastern North American species (probably including R. calendulaceum, R. periclymenoides and R. viscosum) and crossed with the European Pontic azalea R. luteum. Most available plants were probably derived from crosses made originally by a Belgian baker, P. Mortier of Ghent in the 1820-30s. Flowers generally fragrant in large heads, mostly yellow, orange and salmon, to pink and scarlet.

Mollis (Mollis-Sinensis) Azaleas (derived from E Asian species) Derived mainly from the Japanese R. japonicum often with the yellow Chinese R. molle within the parentage. Both of these are large-flowered, short-tubed species, but several other species are probably involved in the history of the group. This group is generally attributed to Belgian nurseryman Louis van Houtte. Flower colours vary through flame reds to salmon oranges and lemon yellows. They had achieved great popularity by the 1870s in the United Kingdom. Early flowering before the Ghents. More recently selections have been made in other countries. Flowers mostly yellow and orange although creams, reds and pinks are also grown.

Knap Hill Azaleas (derived from American-European-Asiatic species) This group includes hybrids that derive from both the Pontic-American group and the E Asian species, many with very bright, rich colours including scarlet, orange, yellow and pink. The young foliage of many cultivars has a purplish hue and it colours well in the autumn. The flowers are generally larger than those of the Ghents and have a longer floral tube. They have in common the fact that they were originally bred in the Knap Hill Nursery, Woking, England, which was managed by the famous Waterer father and son (both named Anthony), although few of the original selections have remained. The original intention was to improve the Ghents by crossing them with R. molle.

Exbury hybrids This range derives from a butter yellow azalea called 'George Reynolds' which was crossed by Lionel de Rothschild at Exbury with a range of unnamed orange-flowered Knap Hill azaleas. Later, R. molle was included by Rothschild in the breeding background of what was to become an extremely successful group, especially in the USA.

Occidentale hybrids The early history of this group is uncertain but those available nowadays comprise a range of similar clones raised in Holland by crossing R. occidentale with Mollis-Sinensis azaleas. All have delicate colours and fragrant flowers.

 

Evergreen Azaleas: These originate from Asia and generally show differences in winter foliage.

 

Indica – Belgian Indian (Indica) Hybrids: Rhododendron indicum, which was the first evergreen azalea to be grown in Europe, was followed by a range of other Chinese and Japanese evergreen species and cultivars (including R. mucronatum) which, by the mid 19th century, had earned the name Indian Azaleas. These early introductions were soon replaced by later selections involving mostly R. simsii, although R. scabrum and other species may be within the parentage of some cultivars. Colours vary mostly from white to pink and through reds to purples and mauves with at least some cultivars extending through the flowering season from late autumn to early summer with a maximum in spring. European breeders used R. simsii, a warm-climate plant from south Asian regions, to produce beautiful tender azaleas for indoor and glasshouse cultivation. They are unsuitable as outdoor plants in much of Europe and North America, but thrive in many Australian gardens and have dominated the azalea market in Australia for several decades. Many have long flowering periods and some are suitable for forcing (see also Wilson, 1990). Cultivars marked sun are suitable for a sunny location.

 

Southern Indica: (these cultivars mostly developed in the SE states of the USA

 

Kurume: A Japanese azalea group originally raised in the early 19th century at Kurume on Kyushu, the southernmost island of Japan. The principal parent species is R. obtusum. The flowers are small and prolific but not without the garish colours of some other groups, ranging through white and pink to reds, mauves and lilacs. Until the early 20th century the karumes were regarded as the only hybrid evergreen azaleas suitable for outdoor cultivation in Europe. These were developed later in the USA and Holland.

 

Modern hybrids: Most modern evergreen hybrids were raised originally by Dutch nurserymen and have R. kaempferi as a dominating parent and flowers from orange to reddish purple and pink. In the mid 20th century the ranks of modern evergreen hybrids were swollen by many clones produced in the United States from a massive hybridisation program involving many species. Several groups have become well known including: Beltsville Azaleas (late flowering), Gable Hybrids American-bred and derived mostly from R. kaempferi, R. mucronatum, R. obtusum and R. pukhanense; Glenn Dale Hybrids American-bred with extensive hybridisation to produce spectacular flowers, often large, frilly-edged double or semi-double; Ilam azaleas from New Zealand mostly rich red or purple—there are others.

In Australia other recognisable groupings include Tall Single Indicas; Satsuki Hybrids, low-growing Japanese hybrids of R. indicum with R. simsii sometimes with striped flowers, Nakaharai Hybrids that flower mostly in December: several are known as Gumpo Hybrids which are low-growing compact plants for cool areas developed in Japan and Taiwan and derived from R. eriocarpum; these are available in a range of flower colours. Other groups include the Gold Cup, Kerrigan, Pericat, North Tisbury and Rutherford hybrids.

Source: Davidson, B.; Craven, L.; Malone, B.; Davidson, R.; Wilson, J, ; Spencer, R. (1997). Rhododendron. In: Spencer, R.. Horticultural Flora of South-eastern Australia. Volume 2. Flowering plants. Dicotyledons. Part 1. The identification of garden and cultivated plants. University of New South Wales Press.