CLERODENDRUM CONUNDRUMS
from ”The Plantsman” RHS
On license from the publisher Mike Grant
Clerodendrumis a large genus of striking plants with a history of over 250 years of cultivation in Europe, and much longer in their native lands. They are known collectively a glorybowers, originally from an American name but now widely adopted. The species are remarkably varied in the form and colour of the inflorescences, foliage and fruit. The slender tubular flowers with long exserted stamens facilitate pollination by butterflies and moths. Additionally, the often brightly coloured calyces and pedicels provide further visual stimulus, driving fertilization and fruit dispersal. This co-evolution has contributed to the diversity which makes them so appealing as ornamentals , captured rather succinctly by Llamas (2003)as the “exotic allure of their fecund natural beauty”.
New research, focusing on the entire geographic range of the genus, is reshaping our perception of the group. Much of this follows the shifted family placement of the genus from Verbenaceae to Lamiaceae (see Wagstaff & Olmstead 1998).
This article outlines the rich historical background to their cultivation, highlights recent developments in our understanding, provides an overview of the most commonly available and notable species.
RESOLVING PAST PROBLEMS
Unfortunately, in common with many other cultivated plants, Clerodendrum has suffered a chronic and widespread lack of correct identification. At the same time there has been a profound misunderstanding of generic and specific limits . Long considered a pantropical and eastern temperate genus, a series of studies within the last decade has shown that sll of the native American species and several of those from Africa and Asia were misplaced in Clerodendrum and were actually members of the related genera (Yuan et al 2010). Notably, one of the African plants, now called Rotheca myricoides (syn. Clerodendrum myricoides, C. ugandense) is widely cultivated, frequently under the cultivar name Clerodendrum myricoides “Ugandense”.
Estimated numbers of species in the genus have varied greatly, ranging from 200 (Riffle 1998) to 350 (Fayaz 2011) and 400 (Wann 2000). Uncertainly regarding the true identities of the numerous published names is now being addressed by us and collaborators at Royal Botanic Gardens Kew. In fact there are closer to 150 species, although more may be discovered in under-explored localities. The cause of multiple names for a given plant was often genuine, due to poor accessibility to literature and lack of comparative material. However some collectors, employed to find novelties for introduction to the West, often described every trivial variation as a new species to bolster their careers. The epithet speciosum alone had been coined four times for different descriptions of new clerodendrum taxa between 1866 1894! Invalid and dubious names are used widely in journals , popular books and websites, and consultation of poor secondary reference sources perpetuates errors. This has lead to confusion, both in taxonomic and horticultural circles, resulting in identical plants being propagated and sold under different synonyms, or erroneously identified and grown with a completely misapplied name (Wearn & Mabberley 2011a).
Recent revisions of African (Verdcourt 1992) tropical American (Yuan et al. 2010) and Malesian (e.g Wearn & Mabberly 2011b) taxa has clarified our understanding.
SUCCESS OF EARLY INTRODUCTIONS AND SUBSEQUENT INERTIA
The first Clerodendrum to reach the UK was C. fortunatum in 1784 from Southeast Asia. this was followed in 1790 by C. chinense (as C. fragrans) and six years later by the so-called “twins” of C.fortunatum C.infortunatum. C. fortunatum. While C fortunatum, “the tree that brings good luck”, is marketed in southern China to treat bruising and other medical applications C. infortunatum was so named due to a superstitious belief that it brought bad luck. The influx of novel genus had begun, culminating in a total of 56 species by the end of 19th century. (Wright & Dewar 1894)
These new “glorybowers” as they were to become known were regularly exhibited as exciting new plants at horticultural shows. As they became more widely cultivated vernacular names were spawned, the most common of which we have included below.
However it is important to mention that of those 56 listed by Wright &Dewar 13 are now considered synonyms. Also, eight species have now been moved out of the genus.. Even leaving with this in mind the number available commercially has declined significantly. There are nine species and five cultivars listed in the RHS Plant Finder 2012-2013, but one (C.myricoides) has been transferred to the related genus Rotheca.
It is likely that the cost of growing these novelties, when balanced against the demands of the consumer market, led to concentration of horticultural effort on a smaller number of the most beautiful species.
However there are exceptions, such as the spectacular C rumphianum. Dismissive reviews, for example, in the Gardeners Chronicle (eg Lindley 1848) must have virtually sealed the fate of some. Clerodendrum capitatum and C. scandens were two such unfortunate species. Lindley compared their rather weaker floral display to with the more spectacular species already in cultivation. They were listed simply as “third rate”.
Historically the demise of certain key nurseries of the Victorian heyday of ornamentals has taken its toll on availability. As many devoted nurseryman retired their establishments passed to others who did not have their flair so with the onset of the First World War labour and fuel cost rose many were lost. Fortunately today many of the less well known taxa are maintained in collections and specialist nurseries around the world.
NOTABLE CULTIVATED TAXA
The horticultural merit of several Clerodendrum is recognised today, as it was 150 years ago. Four have the RHS award of Garden Merit, which are indicated below along with their hardiness rating. The ratings used along with the minimum temperature tolerated, are: H1a (15C degrees ) and H4 (-10C degrees).
Irrespective of their differing hardiness, Clerodendrum benefit from moist, well drained soil and a sunny position, sheltered from strong winds. They can be propagated from cuttings or grown from seed, though some species sucker so root cuttings often produce faster results. While plants in greenhouses may suffer from red spider mite, they are relatively disease free.. The following are the most commonly cultivated taxa. For those not listed in the RHS Plant Finder we have indicated where they might be available.
C. bungei (syn. C. foetidum)Bunge’s glorybower H4
This is a fairly hardy species native from China to Taiwan. It was brought to England from China by Robert Fortune around 1850. It can be grown outside in a sheltered position or as an indoor pot plant. The perfumed pink flowers are held in compact clusters and contrast well with the dark green leaves. It can reach 1.8m high and spreads by suckering. Reduce its size by pruning each spring.
C. Chinense (syns. C. fragnans, C. philippinum),
Chinese glorybower, Hawaiian rose, Honolulu rose, Lady Nugent’s rose stickbush H1a
Probably native to southern China and the Philippines, this species is certainly tender. The cultivated variant usually has double flowers which are fragrant (or pungent depending on one’s nose), white to pale pink, and held in terminal cymes. It can reach a height of around 2m and bears dark green leaves. It has been fittingly described as “a samurai in drag” (Hinkley 2009) because it spreads prolifically via root suckers.
C. paniculatum, pagoda flower. H1a
Introduced from Java in 1809 (Wright &Dewar 1894) this a tender but rewarding ornamental. It produces terminal inflorescences (thyrses, though often erroneously called panicles) up to 45cm long bearing numerous lowers with reddish orange calyces and paler corollas. The large, lobed leaves are a prominent characteristic of this plant. It can grow up to 3m in height. This species produces root suckers, from which it can be readily propagated and will easily strike from cuttings. In cultivation seeds usually do not develop. There is also a pale-flowered selection, C. paniculatum “Album” (cultivated as C. citrinum now synonym of this cultivar), which has lemon-yellow to cream corollas and green inflorescence branches. Although widely available in the U.S (especially in Florida) we have been unable to locate a UK supplier for this species.
C. quadriloculare, Philippine glorybower, starburst clerodendrum H1a
This species is native to the Philippines and New Guinea and was introduced to the UK in the late 19th century. It has clusters of purplish white flowers with long corolla tubes. The elliptic to ovate leaves are dark green above and frequently a distinctive purple on the underside. In the UK, C. quadriloculare is currently available from one Nursery in Cornwell (Cross Common Nursery, pers comm), with small numbers supplied to order.
C. speciosissimum (syn. C buchananii misapplied, C. fallex), Java glorybower. H1a.
First flowering in Europe in the van Geert nursery of Ghent, Belgium in August 1835 this species probably reached the UK soon after. A flowering specimen was collected from Syon Park Middlesex in July 1843 (although named fallax by John Lindley).
The red inflorescences contrast strikingly with the large, heart-shaped glossy dark green leaves, making this a popular glasshouse shrub. It will grow to about 3m in height, requires moist soil and is easily propagated from cuttings and root suckers.
Plants cultivated under the names C. buchananii (misapplied). C. fallax Lindl. (1844) and occasionally as C. blumeanum Schauer (1847 should all be called C. speciosissimum Van Geert ex Drapiez (1836) Clerodendrum buchananii is a commonly misapplied name (which actually relates to a very different plant, Pseudocaryopteris foetida) whereas the others are simply younger synonyms. This clarification should add nomenclatural stability to a much misnamed plant.
C. x speciosum. H1a
Described and first offered by William Bull from his nursery in Chelsea in 1869, this is a hybrid of African C. splendens and Asian C. thomsoniae. It bears most resemblance to the Asian species but with smaller, bright pink calyces.
This hybid and C. thomsoniae are both ideal additions to a conservatory or glasshouse, providing a rampant spread of colour. Both require high humidity and a minimum temperature of 15oC.
C. splendens, flaming glorybower, flaming vine. H1a
This vigorous climber was introduced from Sierra Leone in 1839. The flowers are scarlet and borne in terminal inflorescences. It has elliptic to ovate, glossy, dark green leaves held on short petioles. Although similar in flower to C. speciosissimum, the lea shape, smaller leaf size and climbing habit distinguish C. splendens. It requires full sun but the soil needs to be kept moist, with a minimum temperature of 15C. It makes a suitable patio or container plant if kept in a sheltered position in summer and moved inside in the cooler months. Propagation is by seed or softwood or root cuttings.
C. thomsoniae (syn C.balfourii),bleeding glorybower,bleeding heart vine. H1a
This popular climber was introduced to the UK from West Africa 1861. Each red corolla is framed by a larger, pure white calyx and the ovate leaves are dark green, making it a highly showy plant. Cultivation requirements are the same as those for C. x speciosum.
A hardy deciduous species, this one was introduced from Japan in 1800. It is the one most commonly seen in cultivation outdoors in northern Europe. The habit is of a shrub or small tree with a graceful, rounded shape. The flowers, borne in summer, consist of white corollas surrounded by red calyces. From early August, shiny blue-black fruit is produced, often at the same time as the flowers. The leaves are smaller than those of most other species and are broadly lance-shaped. If the stems or leaves are crushed they emit an odour which has been compared to that of foetid peanut butter.
Several Clerodendrum species formally grown in the West are no longer in cultivation in Europe or America. We have chosen two, particularly colourful in their appearance and history which we believe are candidates for reintroduction into western horticulture.
In 1844 Hugh Low sailed to Borneo in order to collect plants for his family nursery. He first spotted this plant growing along the banks of the Sarawak River. It is a striking plant with large, red inflorescences and heart-shaped leaves and was described by Low in his diary on 2nd April 1845 as “a most superb plant”.. It was collected and sent back to his father’s nursery. It was offered for sale from 1847 until the end of the 19th century.
This species has been largely overlooked since its description by the “Merchant of Ambon”, Eberhard Rumphius over 250 years ago. The accepted date of introduction of C. rumphianum into the UK is 1887 (e.g. Nicholson 1900). Six years later it was offered by the Chelsea nursery to William Bull. It was probably acquired from Javan botanic garden as the species is native only to the Maluku Islands (Moluccas). There have been few excursions into that region since. Fairchild Tropical Garden Exhibition went in 1940. Many superlatives have been ascribed to this plant. American plant collector Hugo Curren went with the Fairchild exhibition, described it as “the most amazing species of this genus I have ever seen, having the showiest spikes of flowers of any kind I ever saw”. Unfortunately it seems to have to have been completely lost to from Western cultivation. The striking, spike-like pyramidal inflorescences of C. rumphianum consist of many reddish bracts and flesh coloured flowers, the latter turning red as they age. Combined with its restricted native distribution, there is significant potential for both reintroduction to horticulture of a beautiful plant and an ex situ conservation effort.
