The Buddleja crispa Complex

In the monograph of Leeuwenberg (1979) and in many subsequent publications (e.g.: Li and Leeuwenberg 1996) several varieties previously classified as separate species were sunk under Buddleja crispa. This "lumping" of so many diverse plants into a single species was debatable and not universally supported. The enthusiasm for seeking out, describing and naming plants in the late nineteenth and early twentieth century led to a number of names often being ascribed to a single species. However, several of those later included under B. crispa by Leeuwenberg differ significantly from each other. Many of these plants (now correctly called varieties) have continued to go by their former species names in horticulture. Mostly they should be labelled as varieties, for example B. agathosma should be correctly known as B. crispa var. agathosma, although that convention isn't used here for convenience.

The ambiguous status of these species or varieties is reflected in the use of the term Buddleja crispa Complex to describe this group of plants (Marquand 1930). The taxonomy of Leeuwenberg has not been revised since 1979, although more recent research has restored species status to at least one B. crispa variety, B. caryopteridifolia (Zhang et al 2014). DNA technology is likely to elucidate and quantify the relatedness (or otherwise) of all the varieties and should replace traditional taxonomy based on observation with the more rigorous phylogeny of DNA sequence analysis. For now it is convenient to split them into the summer flowering, namely B. crispa (species type) and B. caryopteridifolia, and the spring flowering B. agathosma, B. farreri, B. sterniana and B. tibetica.

All these plants share some features such as silvery tomentose foliage and very similar pale lilac to lilac-pink flowers; the justification for classifying all the varieties as a single species is the similarity of the flower morphology. Their natural habitat is the mountainous regions of China including the Himalayas. All are diploid with 38 chromosomes and are often self-compatible. B. crispa varieties hybridise readily with other Asian diploid species and with some African and South American species. Hybrids of B.alternifolia and the B. crispa varieties are particularly numerous including the naturally occuring B. x wardii.

Summer Flowering

Buddleja crispa Species

The commonly available form has very soft grey-green foliage, the leaves are almost heart-shaped with a very short petiole. The flowers are a contrasting lilac-pink and arranged in neat, small panicles. This is an attractive species Buddleja that can grow quite large and woody in the right conditions. It needs a warm south-facing wall or aspect to survive and very good drainage, prefering dryish conditions even in summer to enhance the silvery foliage. It can't take any water-logging over winter. It can be grown in a large pot so it can be brought under cover for winter, although it is still fully deciduous and prone to botrytis (grey mould). It flowers in June-July with a second flush in the autumn if dead-headed.

It has been in cultivation for a long time but so far there is only one recognised cultivar from the USA called Moon Dance (syn.: Hulmoon) described as denser and more compact than the species type. Recently a variegated form has come to light from Stone House Cottage Garden that has regular white leaf margins.

A typical B. crispa flower panicle.
Click for larger image.

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B. crispa foliage.
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B. crispa Stone House Cottage, a variegated form.
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An antique print of B. crispa from
Curtis’s Botanical Magazine, 1854.
Click to enlarge.

Buddleja caryopteridifolia

This species was sunk by Leeuwenberg into B. crispa. Like the species type above it flowers from June until September. It shares a habitat with spring flowering B. crispa varieties in the hot-dry valleys of Sichuan and Yunnan. The foliage is small and silvery, resembling that of B. sterniana (see below), but the growth habit is compact and globose.

It has recently been re-confirmed as a species in its own right (Zhang et al 2014). Flower and leaf morphology are significantly different to the B. crispa varieties and the compositions of the scents are chemically distinct. DNA analysis confirms that B. caryopteridifolia specimens from a series of locations show a greater genetic similarity with each other than with any sympatric B. crispa specimens. The differing phenologies (flowering times) of the two species limits the possibility of genetic exchange between them and contributes to their separation.

The plant was introduced to the UK via the Royal Edinburgh Botanical Gardens but may have become confused with B. sterniana (Cotton 1947). The plant currently being sold in the UK as B. caryopteridifolia appears to be a hybrid of B.alternifolia, possibly B. x wardii or B. x pikei.

Buddleja caryopteridifolia - click for larger image.
Close-up of the flowers.
Photo courtesy of Prof. Weibang Sun,
Kunming Institute of Botany - Chinese Academy of Sciences.



Spring Flowering

Buddleja agathosma

B. agathosma is a large shrub that has the largest leaves of the group. They have toothed margins and are grey felted as with other B. crispa varieties and can be up to 30cm in length. The size and long petiole means they tend hang down The foliage can be variable - the growing tips are almost white but the leaves gradually become more green as the mature. On some stems the leaves have virtually no stipules, whereas elsewhere on the plant the leaves can be connate and entirely encircle the stem.

In the UK climate it is deciduous. The flower buds form in the previous autumn and are held dormant over the winter; they can be dessicated and lost in harsh winters. The flowers can start to open before the foliage reappears in the spring. The individual flower corolla has a greater diameter than the other varieties, up to 8mm. It is usually grown as a wall shrub as it benefits from shelter from the coldest winds, but is quite hardy once established unless water-logged.

B. agathosma flower panicle
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Close-up of the flowers.

Some stems have connate leaves
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Left: the large leaves are distinctive; some stems have virtually no stipules.
Click to enlarge.

Buddleja farreri

B. farreri resembles B.agathosma and is a similar large shrub best grown against a warm wall. The flowers and flowering time are similar but the leaves are smaller with shorter petioles, so are not so pendulous. It is possible that the two varieties have been confused in the past and their similarity suggests they are indeed variations of the same species.


Right: Buddleja farreri flowers
- click for larger image.
(Photo by Andrew Brookes)

Buddleja sterniana

B. sterniana has features in common such as toothed, felted foliage with the two species above but the flowers and leaves are on a much smaller scale. It forms a smaller shrub with a more brached habit and is deciduous in all but the mildest locations. The flowers open just as the leaves begin to sprout again, late March to April in the UK. It is hardy but the flower buds form in the autumn and are exposed over the winter so can be lost to cold winds. Sometimes the flowers start to open in the autumn if the weather is particularly mild but are soon killed by the first frosts.

The original plants were from seeds brought to Edinburgh by George Forrest but by the end of the Second World War only a single specimen survived in the chalk garden of Colonel Stern, for whom the plant is named. The origin is uncertain but probably Yunnan province (Cotton 1947).

Buddleja sterniana flowers - click for larger image.
Close-up of the flowers.

The foliage is much smaller than other varieties - click for larger image.


Left: the flower buds have to over-winter - click for larger image.


Buddleja tibetica

B. tibetica is not as widely grown as the other spring-flowering B. crispa varieties as it is more demanding about conditions. It has evolved to be more xerophytic as it comes from dry valleys on the Tibet plateau and the persistent tomentum is more dense to cope with the dessicating winds, giving the leaves a grey to white appearance. It was originally discovered at an altitude of 3,300 metres in the Llalang Valley. As a result it doen't take to the damp UK climate.

The flowers appear before the foliage in the spring and open a dark-lilac but gradually fade and can become almost white. It is the earliest flowering of the B. crispa varieties (Cotton 1947).

It has also been known by the synonym Buddleja hastata.


(Photo by Andrew Brookes)

Buddleja tibetica flowers - click for larger image.
Close-up of the flowers.

Hybrids

Leeuwenberg (1979) considered Buddleja x wardii to be a perfect intermediate between B. alternifolia and B. crispa and a naturally occuring hybrid of the two. The foliage can be alternate or opposite. No specimens are known to be held in any of the collections.

The plant that is sold commercially in the UK as B. caryopteridifolia is probably a hybrid of B. alternifolia x B. crispa as the leaves can be both oppposite and alternate, and they have the same distinctive scent as B. alternifolia but less felted than B. crispa. It is a smallish, highly branched and deciduous shrub. The flowers are intermediate between the parent species and it can flower both in early summer (May-June) and again in the autumn (September-October). Whether this is an example of B. x wardii or another similar hybrid is uncertain, and it can only be tentatively identified as B. x wardii.

Other similar hybrids have been artificially bred. Buddleja × pikei was bred by A.V. Pike at Hever Castle, Kent and is the cross B. alternifolia and one of the B. crispa varieties, probably an authentic specimen of B. caryopteridifolia. The best of the seedlings was named B. pikei 'Hever'.


Longstock Gem is a late spring flowering hybrid of B. agathosma x B. alternifolia. (Photo by Peter Moore.)
Click to enlarge.

This plant, sold as B. caryopteridifolia, is a hybrid of B. alternifolia and B. crispa but its origin is unknown.
Click to enlarge.


Peter Moore at the Longstock Park Nursery has bred a number of similar hybrids: 'Autumn Surprise' (B. crispa x B. alternifolia Argentea) that flowers in the autumn; 'Longstock Gem' (B. agathosma x B. alternifolia) that flowers on May just before B. alternifolia; and Longstock Silver (B. agathosma x B. alternifolia), a plant shy to flower and grown primarily for its very silver foliage.

A hybrid of B. crispa and B. alternifolia from The Lavender Garden.
Click to enlarge.

A B. alternifolia hybrid with an unidentified B. crispa variety has recently arisen in The Lavender Garden collection. It is similar to the tentatively identified B. x wardii above but with softer, grey foliage that can be alternate, opposite or slightly offset. The flowers are intermediate between the species but in a panicle more like B. crispa. The flowering time, in common with several of the other hybrids mentioned, is late summer rather than the spring.

Two hybrids with B. lindleyana, very similar to each other, are 'Longstock Pride' and 'Pride of Hever'. The B. crispa genes are not very evident as the foliage is much the same as B. lindleyana and the flowers are in panicles that resemble neither parent, although the same colour as B. lindleyana . Another B. crispa hybrid is 'Bel Argent', a French cross with B.davidii.

'Salmon Spheres' is a very attractive hybrid with the South American B. globosa. It grows quite large and flowers both spring and autumn. Silver Anniversary (Morning Mist) is a cross of B. crispa with the South African B. loricata that remains small and flowers mostly in the late summer. Both these hybrids have soft, silvery foliage inherited from B. crispa although otherwise they more resemble the other parent.

Buddleja 'Silver Anniversary'
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Buddleja 'Longstock Pride'
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Buddleja 'Salmon Spheres'
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Complete list of B. crispa synonyms:

Buddleja acosma Marquand
Buddleja agathosma Diels
Buddleja agathosma var. glandulifera Marquand
Buddleja caryopteridifolia W. W. Sm.
Buddleja caryopteridifolia var. eremophila (W. W. Sm.) Marquand
Buddleja caryopteridifolia var. lanuginosa Marquand
Buddleja crispa var. farreri (Balf. f. et W. W. Sm.) Hand. - Mazz.
Buddleja eremophila W. W. Sm.
Buddleja farreri Balf. f. et W. W. Sm.
Buddleja hastata Prain ex Marquand

Buddleja incompta W. W. Sm.
Buddleja praecox Lingelsh.
Buddleja sterniana A. D. Cotton
Buddleja tibetica W. W. Sm.
Buddleja tibetica var. farreri (Balf. f. et W. W. Sm.) Marquand
Buddleja tibetica var. glandulifera Marquand
Buddleja tibetica var. grandiflora Marquand
Buddleja tibetica var. truncatifolia (Lévl.) Marquand
Buddleja truncata Gagnep.
Buddleja truncatifolia Lévl.


References

Cotton, A. D. (1947). Spring flowering buddleias. RHS Journal Vol. 72. 1947. pp 427 – 437. Royal Horticultural Society, London. (Available HERE.)

Leeuwenberg, A.J.M. (1979) The Loganiaceae of Africa XVIII Buddleja L. II, Revision of the African & Asiatic species. H. Veenman & Zonen B. V., Wageningen, Netherlands. (Selected pages HERE.)

Li, P. T. & Leeuwenberg, A. J. M. (1996). Loganiaceae, in Wu, Z. & Raven, P. (eds) Flora of China, Vol. 15. Science Press, Beijing, and Missouri Botanical Garden Press, St. Louis, USA

Marquand C.V.B. (1930) Revision of the old world species of Buddleja. Kew Bulletin 1930: 177–208.

X. Zhang, G. Chen, W. Gong, & Weibang Sun (2014) Buddleja caryopteridifolia (Scrophulariaceae), a species to be recognized based on morphology, floral scent, and AFLP data. Phytotaxa 161: 181-193.


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