PlantLife Volume 56.6, December 2023. The genus Wisteria

 

The genus Wisteria – a guided tour

Brian Schrire

with

James Compton, Kate Grieve, Geoff Nichols and Susyn Andrews

 

“Wisterias need little introduction, being easily recognised

by gardeners and non-gardeners alike. When adorned with

their spectacular clusters of flowers there are few other

climbers that can compare. They are familiar plants in towns

and villages where they can be seen adorning house walls or

creating an impressive garden feature”.  Compton & Lane (2019).

Wisteria comprises four species encompassing a major disjunction between the single American species, W. frutescens (L.) Poir. and three east Asian species. Wisteria sinensis (Sims) DC. is restricted to eastern China while W. floribunda (Willd.) DC. and W. brachybotrys Siebold & Zucc. (= W. venusta Rehder & E.H. Wilson), occur in southern Japan with W. floribunda also extending into South Korea. For an explanation of the origin and spelling of the name Wisteria, see Compton & Lane (2019: 44–43).

Wisteria floribunda 'Blue Dream'

Wisteria frutescens (American wisteria) was the first to be introduced into cultivation in Europe, in 1724, followed by W. sinensis (Chinese wisteria) in 1816, W. floribunda (Japanese wisteria) in 1830 and W. brachybotrys (silky wisteria) in the 1840’s (Compton 2015; Compton & Lane 2019).

The genus Wisteria Nutt. (1818) is one of 14 genera in Tribe Wisterieae Zhu (1994), with most species being tropical Asian climbers and woody lianas (Compton et al. 2019; Duan et al. 2021). Wisteriopsis J. Compton & Schrire and Nanhaia J. Compton & Schrire, however, both from China to North Vietnam, contain warmer temperate to subtropical species, but Wisteriopsis japonica (Siebold & Zucc.) J. Compton & Schrire (= Wisteria japonica Siebold & Zucc.), with creamy-yellow flowers, is the only other temperate species in the tribe, occurring in Japan.

Fig. 1: Left - woody liana stems of Wisteria sinensis (stems twining anti-clockwise); stems of W. frutescens and W. brachybotrys also rotate anticlockwise. Right - Wisteria floribunda (stems twining clockwise) as do the hybrids W. x formosa and W. x valderi.

The tribe Wisterieae (Leguminosae – Fabaceae) is distinguished by the climbing habit (Fig. 1), the floral bracts that for the most part enclose the buds at the tips of the inflorescences (Fig. 2) and the presence of true panicles or racemes of flowers (Fig. 3). Flower pedicels are singly attached to the inflorescence axis in true racemes or panicles, whereas pedicels are attached in pairs, or more, on the inflorescence axis in pseudopanicles or pseudoracemes (Fig. 3). Such inflorescences characterise similar looking species in the more distantly related tribes Millettieae Miq. and Phaseoleae (Bronn.) DC. (Geesink 1984; Lewis et al. 2005). For a more detailed discussion of the relationships of tribe Wisterieae to these latter tribes, see Compton et al. 2019: 3–8.

Fig. 2: Characteristic broad bracts enclosing young flower buds in top left - W. sinensis; top right - W. floribunda; bottom left - W. frutescens and bottom right - W. brachybotrys. 

Fig. 3: Left - pseudopaniculate inflorescence (with enlarged inset) of Millettia extensa (Benth.) Benth. ex Baker (Photo: Sawai Mattapha). Note paired pedicels behind bracts on inflorescence axis. Right - racemose inflorescence of W. frutescens subsp. macrostachya (Nutt. ex Torr. & A. Gray) J. Compton & Schrire. Note single pedicels arising from inflorescence axis.

The only two species to overlap in their native distribution are W. brachybotrys and W. floribunda, but no evidence exists of naturally occurring hybrids between them. In cultivation, however, several hybrids have arisen, and the various cultivars produced are grouped under the name W.× valderi J. Compton (Compton 2015), the epithet honouring Peter Valder, an Australian plantsman and wisteria enthusiast (Valder 1995). Wisteria × formosa Rehder (1922), includes cultivars resulting from crosses between W. sinensis and W. floribunda in cultivation. Both hybrids have clockwise twining stems indicating the dominance of W. floribunda over the other two anti-clockwise twining parents and this helps distinguish them from the similar looking, but anti-clockwise twining, cultivars of either W. brachybotrys or W. sinensis.

  

Fig. 4: Wisteria flowers; top left - Wisteria frutescens subsp. macrostachya ‘Pondside Blue’ noting the largest (standard) petal somewhat flexed over the wings and keel, with the wing petals contiguous at the apex, forming a downward curving “hood” clasping the visible keel tip; bottom left – floral parts of W. frutescens subsp. frutescens ‘Longwood Purple’, showing the standard petal in the bottom row with the basal part of the blade (above the narrow claw) leading to a raised, ridge callosity (area of thickening) below the central yellowish nectar guide; the upper two rows showing a range of keel petals (left block of four) and wing petals (right block of four), the base of each petal blade showing a lower narrow claw and upper narrow auricle; bottom right – Wisteria floribunda ‘Domino’, noting the standard petal is reflexed away from the wings and keel, with the wings positioned alongside the keel, not contiguous apically, so that the exposed keel tip is visible between the wings but not clasped by them; also note the two pointed callosities at the area of articulation at the base of the standard above the wings; top right – petals of W. brachybotrys, the standard on the lower row showing pointed callosities and similar left block of four keel petals and right block of four wing petals.

Fig. 5: Wisteria brachybotrys: W. brachybotrys 'Okayama' (top left); W. brachybotrys 'Showa-Beni' (top right); W. brachybotrys f. albiflora 'Shiro-kapitan'(bottom)

Fig. 6a: W floribunda 'Blue Dream'

Fig. 6b: W. floribunda 'Kimono'

Fig. 6c: W. floribunda 'Kokuryu'

Fig. 6d: W. floribunda f. alba 'Shiro-noda'

Fig. 6e: W. floribunda f. multijuga 'Cascade'

Fig. 6f: W. floribunda f. pleniflora 'Yae-kokuryu' (= ‘Violacea Plena’; ‘Double Black Dragon’)

Fig. 6g: W. floribunda f. rosea 'Hon-beni' 

In South Africa, Wisteria is cultivated throughout the cool temperate regions, except for the subtropical section along the eastern coast. It can be found from Springbok on the west coast, southwards to Cape Town and surrounds, across the Western Cape and along the Garden Route to Port Elizabeth and the Eastern Cape interior, inland to Kokstad and the KZN midlands, northwards to Gauteng, Mpumalanga and as far east as Phalaborwa in the Northern Province.  Wisteria does best where there are cold winters and it copes with both summer or winter rainfall although moderate watering is required in drought conditions.  It has adapted well to conditions in South Africa, to the extent that it has become a problem plant in some areas because of its robust growth and invasive, aggressive roots that can weaken surrounding structures like paving and walls (https://www.ecosystemgardening.com/chinese-wisteria.html).

A brief survey of the wisterias currently grown in South Africa revealed that the most common species is the Chinese wisteria, W. sinensis, with the cultivars ‘Prolific’, ‘Amethyst’ and ‘Texas Purple’ (possibly introduced from the US) being most frequent.  Pretoria has one of the silky wisteria cultivars, W. brachybotrys 'Shiro-kapitan. There is also an observation of one of the hybrids between W. floribunda and W. brachybotrys, i.e. W. x valderi 'Eranthema' (https://www.inaturalist.org/observations/185388127). At this stage there is no evidence that new cultivars have emerged in South Africa and further investigation is required to confirm this.

Fig. 7a: W. frutescens 'Amethyst Falls'

Fig. 7b: W. frutescens subsp. macrostachya 'Aunt Dee'

Fig. 8a: W. sinensis 'Amethyst'

Fig. 8b: W. sinensis 'Prolific'

Fig. 8c: W. sinensis 'Texas Purple'

 

Fig. 9a: W. x formosa 'Caroline'

Fig 9b: W. x formosa 'Enchantment'

Fig 10a: W. x valderi 'Burford'

 

Fig. 10b: W. x valderi 'Lavender Lace'

The following key should aid identification of Wisteria that you encounter or grow in your garden.

KEY:

Group 1 : Flowers with standard petal flexed somewhat over the wings and keel, with the wing petals contiguous at the apex, forming an arching “hood”, clasping the visible keel tip (Fig. 4, top left), the stamens emerging halfway down keel tip into the gap created by the wings during pollination; standard petal 1.5–2 x c. 2 cm, broadly rounded, with two ridge-like callosities at the base encircling a hollow tube-like space above the claw (Fig. 4, bottom left); pods glabrous, the seeds attached to a pale brown membranous inner seed coat (endocarp), seeds kidney-shaped to oblong, only slightly flattened; distribution: eastern states of USA; young stems reddish-brown, twining anti-clockwise; inflorescences of congested broad racemes 8–30 cm long; bracts large, ovate-lanceolate, acuminate 0.8–1.2 cm long, to 5 mm wide, pubescent, often with glandular hairs

Wisteria frutescens

Pedicels and calyx with simple and only a few clavate (club-shaped) glandular hairs; calyx teeth subequal, all acute; inflorescences 8–15 cm long; from Connecticut, Delaware, Illinois, Indiana, Iowa, Maryland, Massachusetts, Michigan, Missouri, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, Virginia and West Virginia

subsp. frutescens

Pedicels and calyx densely covered in simple and clavate glandular hairs; upper lip of calyx with acute teeth, lower lip of calyx longer, teeth acuminate; inflorescences (8)10–30 cm long; from Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi, Oklahoma, South Carolina, Tennessee and Texas

                                                                              subsp. macrostachya

Group 2: Flowers with standard petal reflexed away from the wings and keel, with the wings positioned alongside the keel, not contiguous apically, so that the exposed keel tip is visible between the wings but not clasped by them (Fig. 4, bottom right), the stamens emerging at the flower tip and wings splaying away from keel during pollination in Asian Wisteria; standard petal with pair of hard pointed callosities at the base of blade above the claw (Fig 4, top right); pods velutinous to pubescent, the flattened, lens-shaped seeds embedded in a spongy endocarp; distribution: Eastern China to South Korea and southern Japan

Clockwise rotation of climbing stems (Fig. 1)

 

Inflorescence axis not extending on maturity, flowers opening more or less simultaneously, standard petal more than 2 cm wide                                                                                                           

                                                                     Wisteria × valderi

 

Inflorescence axis extending ± continuously apically on maturity, flowers opening in succession from base to apex, standard petal less than 2 cm long and wide

 

Inflorescences 18–120 cm long, standard petal ovate, 8–15 x 8–12 mm; bracts linear-acuminate to narrowly lanceolate 5–12 x 2–6 mm; stems grey, leaves and stems sparsely pubescent when young, glabrescent; leaflets (11–)13–15; pedicels 5–30 mm long; calyx 3–5 mm wide

                                                                            Wisteria floribunda

Inflorescences 20–35 cm long, only slightly extending on maturity; bracts narrowly to broadly lanceolate, intermediate in width between W. floribunda and W. sinensis                                                                    

       Wisteria × formosa

 

Anti-clockwise rotation of climbing stems (Fig. 1); inflorescences not extending on maturity, flowers opening ± simultaneously; standard petal suborbicular, more than 2 cm long and wide, 20–30 x 20–30 mm; leaflets 9–11(–13)

 

Stems reddish-brown; racemes broadly club-shaped, 8–25 cm long; bracts broadly ovate-lanceolate 15–23 x 8–15 mm, papery, sericeous; young leaves and inflorescence rachis densely pubescent; pedicels 15–50 mm long; calyx 4–8 mm wide

                                                                            Wisteria brachybotrys

 

Stems grey; racemes narrow, ± cylindrical, (12–)15–40 cm long; bracts narrowly ovate to lanceolate, acuminate, 5–20 x 5–10 mm, membranous; young leaves and inflorescence rachis sparsely pubescent, glabrescent; pedicels 15–20(–30) mm long; calyx 3–5 mm wide

                                                                            Wisteria sinensis

 

References

Compton J. (2015). The genus Wisteria Nuttall. Leguminosae (Fabaceae). Curtis’s Botanical Magazine 32(3–4): 183–192. Wiley-Blackwell, UK.

Compton, J. & Lane, C. (2019). Wisteria – The Complete Guide. RHS Horticultural Monograph 3. Royal Horticultural Society, UK, 303 pp.

Compton, J., Schrire, B.D., Konyves, K., Forest, F., Malakasi, P., Mattapha, S. & Sirichamorn, Y. (2019). The Callerya Group redefined and Tribe Wisterieae (Fabaceae) emended based on morphology and data from nuclear and chloroplast DNA sequences. Phytokeys 125: 1–112. https://doi.org/10.3897/phytokeys.125.34877.

Duan, L., Li, S-J., Su, C., Sirichamorn, Y., Han, L-N., Ye, W., Lôc, P.K., Wen, J., Compton, J.A., Schrire, B.D., Nie, Z-L. & Chen, H-F. (2021). Phylogenomic framework of the IRLC legumes (Leguminosae subfamily Papilionoideae) and intercontinental biogeography of tribe Wisterieae. Molecular Phylogenetics and Evolution 163, 107235. 10.1016/j.ympev.2021.107235 - DOI - PubMed.

Geesink, R. (1984). Scala Millettiearum. Leiden Botanical Series 8. pp. 131. E.J. Brill, Leiden University Press, Leiden.

Lewis, G., Schrire, B., Mackinder, B. & Lock, M. (eds.) (2005). Legumes of the World. Royal Botanic Gardens, Kew. 577 pp.

Nuttall, T. (1818). The Genera of North American Plants. Vol. 2. D. Heartt. Philadelphia, 268 pp.

Rehder, A. (1922). Wisteria × formosa, new species, varieties and combinations from the herbarium and the collections of the Arnold Arboretum. J. Arnold Arbor. 3: 36.

Valder, P. (1995). Wisterias – a comprehensive guide. Timber Press, Portland, Oregon. USA, pp. 160.

Zhu, X-Y. (1994). Wisterieae, a new Tribe of the family Leguminosae – with special reference to its pollen morphology. Cathya 6: 115–124.

 About the Author

Brian Schrire arrived in KwaZulu-Natal in 1980, from the (then) Botanical Research Institute in Pretoria (now SANBI), to take up a position as Officer-in-charge of the Botanical Research Unit and Curator of Natal Herbarium in Durban. Among various objectives, priority was given to establishing a Quick Guide, mini-herbarium, separate from the main collection, to aid and speed up identifications; as well as initiating a fieldwork programme targeting gaps in the collections from the many bioregions in the province.

With a research interest in the Fabaceae, particularly tribe Desmodieae (undertaken for an MSc. at the University of Durban-Westville) and Indigofera (PhD. at the University of Natal), one of the focus areas for plant collecting was the Pondoland Centre of Endemism. The ex Natal Herbarium Curator, Mr Rudolf Strey had collected intensively in the Pondoland region and he became a mentor introducing the author to Mr Nicholson and others with expert knowledge of the plants of the region. Thus began a close association between the Umtamvuna area and Natal Herbarium also involving Geoff Nichols from the Durban Botanic Gardens, Tony and Maggie Abbott, Marie Jordaan, Cyril Buthelezi and Mphikheni Ngwenya from Natal Herbarium and Braam Van Wyk at the University of Pretoria. In 1985, Brian was transferred to the Royal Botanic Gardens, Kew, in London for three years, as the South African Botanical Liaison Officer and on completion of his PhD. in 1990, he returned to the UK to take up a staff position at Kew