Rhododendron: The Hybrids / Introduction The Hybrids / Introduction

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Article from Bean's Trees and Shrubs Hardy in the British Isles

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'Rhododendron: The Hybrids / Introduction' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/rhododendron-the-hybrids-introduction/). Accessed 2024-03-28.

Family

Glossary

authority
The author(s) of a plant name. The names of these authors are stated directly after the plant name often abbreviated. For example Quercus L. (L. = Carl Linnaeus); Rhus wallichii Hook. f. (Hook. f. = Joseph Hooker filius i.e. son of William Hooker). Standard reference for the abbreviations: Brummitt & Powell (1992).
authority
The author(s) of a plant name. The names of these authors are stated directly after the plant name often abbreviated. For example Quercus L. (L. = Carl Linnaeus); Rhus wallichii Hook. f. (Hook. f. = Joseph Hooker filius i.e. son of William Hooker). Standard reference for the abbreviations: Brummitt & Powell (1992).
clone
Organism arising via vegetative or asexual reproduction.
compound
Made up or consisting of two or more similar parts (e.g. a compound leaf is a leaf with several leaflets).
hybrid
Plant originating from the cross-fertilisation of genetically distinct individuals (e.g. two species or two subspecies).
included
(botanical) Contained within another part or organ.
interspecific
(of hybrids) Formed by fertilisation between different species.
section
(sect.) Subdivision of a genus.

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Credits

Article from Bean's Trees and Shrubs Hardy in the British Isles

Recommended citation
'Rhododendron: The Hybrids / Introduction' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/rhododendron-the-hybrids-introduction/). Accessed 2024-03-28.

INTRODUCTION

In this section an attempt has been made to give a reasonably comprehensive account of the hybrids of Rhododendron available to growers at the present time. The hybrids have always outnumbered the species in gardens, and it was felt by the editors that to ignore them would greatly lessen the value of this revised edition. The hybrids (including azaleas) currently in commerce number over a thousand and it is obviously impossible to include them all. Hybrids listed by only one nurseryman have been excluded unless they have received an award or have such obvious merits that they are certain to become more widely available. Space has been given to hybrids of historical interest and to certain old hybrids which, though no longer in commerce, are still to be found in gardens. The descriptions are in the main based on living material, and we are most grateful to the garden owners and managers who have helped to make this possible. Descriptions of some of the older hybrids are taken from the manuscript notes compiled by Arthur Ivens, kindly made available by Messrs Hillier. Mr Ivens’ meticulous descriptions, mostly quite as detailed as those given to species by botanists, have also proved most valuable for verifying the identity of certain Hardy Hybrids whose correct name was in doubt. Some descriptions are drawn from those published by the Royal Horticultural Society when the hybrid received an award. The historical notes are the product in the main of research in the files of The GardenersChronicle since 1841, and study of original descriptions in horticultural publications. But the two volumes on Rhododendron by J. G. Millais are the souce of much information on the hybrids raised in the late 19th century and the early part of the present century. Millais was the chronicler of the rhododendron world of his time, and these two volumes, cumbersome and rather carelessly compiled though they are, are a storehouse of interesting information, and a monument to the intelligent affection that the genus Rhododendron has inspired in so many of its devotees.

Nomenclature of Hybrids. – For the most part hybrids in the genus Rhododendron have been named in the same way as other perennial plants. The names of Hardy Hybrids, most azaleas, etc., indicate clones, i.e., plants propagated vegetatively and derived from a single mother-plant. These names are usually ‘fancy’ names, but some of the older hybrids (and a few later ones) bear clonal names in Latin, e.g., ‘Album Elegans’ and ‘Everestianum’. The standard practice worked well enough for commercial hybrids, few of which were primary crosses and mostly were of unrecorded or at least undeclared parentage. But the hybrids raised in private gardens from the early years of this century onwards were the result of deliberate crosses and therefore of known parentage. These came to be named according to the system already in use among orchid breeders, by which the products of a cross receive a collective ‘fancy’ name, which remains constant no matter how many times or where the cross is made, and any seedling of the cross worthy of distinction is given a clonal name, also in the vernacular, which belongs solely to it and its vegetatively propagated progeny. A group of seedlings and clones having a common parentage came to be known as a ‘grex’ (Latin for herd or flock), a term also borrowed from the orchidists.

As an example of this system, in the modified form that came into force in the 1950s, we may take the hybrid between R. dichroanthum and R. griersonianum originally made at Bodnant. The ‘grex-name’ for this cross is Fabia. Named clones from this cross are Fabia ‘Minterne Apricot’ (raised at Minterne), Fabia ‘Roman Pottery’ (raised at Embley Park) and several others. A confusing feature of this system of nomenclature, as it has been applied to rhododendrons, is that the collective or grex-name may also be used in a clonal sense. Thus the name ‘Fabia’, as distinct from grex Fabia, would belong to the clone, if any, descended from the plant which received an Award of Merit when shown by the raiser in 1934 as R. Fabia simply. Fabia, the example so far used, is a straight cross between two species, but many registered grexes have a hybrid as one parent, e.g., the famous Naomi grex, which has four species in its parentage, and a few are the result of hybrid with hybrid crosses, e.g., the Jalisco grex, also a compound of four species.

The system of nomenclature discussed here was first adopted by Lionel de Rothschild in 1931 and became the official method of naming rhododendron crosses when the Rhododendron Stud Book was issued in 1934 (in the Year Book of the Rhododendron Association for that year). Its abandonment was officially proposed in a note published in the Rhododendron and Camellia Year Book for 1956 (pp. 156–9), and put into effect around 1959, since when only clonal names have been accepted for registration by the Royal Horticultural Society, which is the International Registration Authority for Rhododendron. However, most of the important interspecific crosses were named as grexes, and the system was applied retrospectively to some earlier ones, so there is an inheritance of well-established grex-names that cannot now be conveniently abandoned. If a name is stated in the International Register to be a grex-name it is so treated in the descriptions that follow, and the formula-name, i.e., the statement of parentage, is placed immediately after it; grex-names are given without inverted commas, to avoid confusion with clonal names. In the formula, the parents are given in alphabetical order, as is now customary; the old convention, by which the seed-parent was given first, is impracticable, since in many cases it is not known which way round the cross was made, and some crosses have been made both ways.

Considering the size of the genus, and the amount of hybridising that has been done, it is at first sight surprising how very few interspecific crosses bear valid botanical names. The explanation is that botanical names for garden hybrids are usually acquired fortuitously; commercial hybrids in some groups were given Latin names by their raisers, and if these were supported by an adequate description, they came to be accepted as botanically valid. However, in Rhododendron the ‘Latin phase’ of naming was a short one (virtually all hybrids raised after 1850 bear ‘fancy’ names) and in any case the vast majority of interspecific crosses were named according to the system discussed above, and consequently bear names such as Angelo, Fabia, and Elizabeth. In the interests of consistency, the few crosses that bear valid botanical names are included in this section, instead of being treated with the species as in previous editions, and their names are given as in the International Rhododendron Register. Thus R. × praecox Carr., the valid botanical name for R. ciliatum × R. dauricum, is given as Praecox and in effect regarded as a grex-name that happens to be in Latin instead of in the vernacular.

Another method of naming hybrids is the condensed formula, e.g., Oreocinn as a substitute for R. oreotrephes × R. cinnabarinum. This method was used by Edward Magor of Lamellen for his hybrid grexes, and the results were treated with derision by his fellow rhododendron breeders, who with good reason prided themselves on choosing elegant and memorable names for their crosses. Some of the Magor names were indeed most uncouth – Smirnauck and so on – but his son Major Walter Magor has recently pointed out that this system of naming was actually proposed by no less an authority than Sir Isaac Bayley Balfour of the Royal Botanic Garden, Edinburgh (R.C.Y.B. 1966, p. 135). The same method was used by a few other breeders, though on a lesser scale, and has now been abandoned.

Awards. – As throughout this work, the abbreviation A.M. stands for the Award of Merit, and F.C.C. (a higher award) for First Class Certificate, both being granted by the Royal Horticultural Society. The abbreviations A.M.T. and F.C.C.T. indicate the equivalent awards given to rhododendrons and azaleas after trial in the garden of the Royal Horticultural Society at Wisley in Surrey (or at Exbury in Hampshire in the case of a few early trials). Before 1923, rhododendrons and azaleas were judged by the Society’s Floral Committee. In 1924 this was divided into two subcommittees, and to subcommittee B (Floral B) was entrusted the judging of ornamental trees and shrubs, and ‘botanical species’; its first chairman was Gerald Loder of Wakehurst Place, Sussex. After the formation of the Rhododendron Association the judging of rhododendrons and azaleas was transferred to a joint committee of the Association and the Royal Horticultural Society, which started work in 1931. Shortly after the second world war, the Rhododendron Association was dissolved and its functions transferred to the Rhododendron Group of the Royal Horticultural Society. At the same time the Rhododendron Joint Committee became a Standing Committee of the Society and since 1953 has also judged camellias.