Senna spectabilis
(whitebark senna)

Preferred Common Name

• whitebark senna

Variety

• Senna spectabilis var. excelsa (Schrad.) H. S. Irwin & Barneby
• Senna spectabilis var. spectabilis

Other Scientific Names

• Cassia excelsa Schrad.
• Cassia humboldtiana DC.
• Cassia spectabilis DC.
• Pseudocassia spectabilis (DC.) Britton & Rose

International Common Names

• English: calceolaria shower; spectacular senna
• French: casse remarquable; séné spectaculaire
• Chinese: mei li jue ming

Local Common Names

• Belize: pisabed
• Bolivia: aceitón; aceitón ordinario; carnaval; hediondillo; limoncillo; pacaisillo; pajarilla amarillo; ramo
• Cuba: algarrobillo; palo bonito
• Dominica: palo de burro
• Dominican Republic: bruscón; cañafistol; chácaro; libertad; palo de burro; pela burro
• Haiti: casse marron; kas mawon (Creole)
• Kenya: mhomba; momba; mwenu
• Malaysia: antsoan dilaw; cassia; mhomba; mwenu; Panama-ngu; scented shower
• Nicaragua: candelillo
• Philippines: antsoan-dilau; palucheba
• Puerto Rico: casia amarilla
• USA: calceolaria shower; yellow shower

EPPO code

• CASSP (Cassia spectabilis)

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Fabales
•                         Family: Fabaceae
•                             Subfamily: Caesalpinioideae
•                                 Genus: Senna
•                                     Species: Senna spectabilis

Until the beginning of the 1980s the Cassia genus was considered to be a very large genus of over 500 species. Bentham (1871) wrote that three groups within the Cassia genus were so distinct from one another that any species can always be unequivocally allocated to one of them; some main distinctions included fruit structure, stamen structure and arrangement, and nodulation (Lock, 1988). However it was not until 1982 that Irwin and Barneby formally separated Cassia into three genera: Cassia L. emend. Gaertner, Senna Miller, and Chamaecrista Moench. Cassia now has only about 30 species, whereas Senna and Chamaecrista comprise about equal numbers of species, about 260 and 270 respectively (Irwin and Barneby, 1982).These three genera are now largely accepted and together make up the subtribe Cassinae. Cassia and Senna differ principally in stamen organization, and in arid areas of Australia, taxonomic distinctions between and within the three genera are blurred by polyploidy, hybridization and apoximis (Lewis et al., 2005). In 1988, Lock presented new names and combinations for the Cassinae species in Africa, noting that “if Cassia were to continue to be used in its broad sense in Africa, there would be several species which would be consistently given different names in different continents” (Lock, 1988). Approximately 80% of the Senna genus’ 260 or so species occur in New World tropical and subtropical areas, extending into warm temperate and rarely into cool temperate areas of both hemispheres with species in Africa, Madagascar, Australia, and a few in southeastern Asia and Pacific islands (Irwin and Barneby, 1982; Lock, 1988; Wagner et al., 2014). 

Identification in historical literature can be difficult due to genus name changes, as well as some of S. spectabilis’ synonyms which include Cassia speciosa Kunth (not to be confused with Cassia speciosa Schrad. =Sennamacranthera var. micans (Nees) H.S.Irwin & Barneby). Isely (1975) described a provisional division of Cassia excelsa from C. spectabilis based on C. excelsa’s more ample flowers and longer pedicels and pods (defined primarily by relatively numerous obtuse leaflets) than C. spectabilis; however, Irwin and Barneby (1982) argue the two species cannot be clearly distinguished, citing the overlap in measurements, and have instead described these differences as two varieties within the species: S. spectabilis var. excelsa is the Brazilian population with generally two or three more pairs of generally smaller and more obtuse leaflets than var. spectabilis and flowers often, but not consistently, larger (Irwin and Barneby, 1982). Also, S. spectabilis var. spectabilis is commonly cultivated, while var. excelsa is rarely cultivated (PIER, 2014).

Tree to 10 or more metres high, the branchlets usually tomentose when young. Leaves moderately large, an average leaf about 20-foliolate; petiole short, pubescent, eglandular; rachis usually about 2 dm. long, eglandular and otherwise like the petiole; leaflets several to many pairs, lanceolate, 3-8 cm. long and usually about 2 cm. wide, acute apically, obtuse basally, pubescent below, especially along the veins, puberulent to subglabrous above and less dull than below, opposite on the rachis, with 10 or more pairs of prominent lateral veins; petiolules 2-3 mm. long, pubescent. Inflorescence of several terminal or subterminal several-flowered racemes; bracts lanceolate, a few mm. long, caducous. Flowers yellow; sepals 5, obovate-orbicular, markedly unequal, up to 1 cm. long and broad, glabrous to lightly puberulent; petals 5, mostly obovate, markedly unequal, up to 2.5 cm. long and 1.5 cm. broad, subglabrous, venose, short-clawed; stamens 10, 3-morphic; the 3 lowermost the largest, their anthers oblong, about 7 mm. long, short-rostrate apically and dehiscent by terminal pores, the loculi somewhat converging terminally; anthers of 4 median stamens 5-6 mm. long, similar to the 3 lowermost except the rostrum reflexed and the loculi divergent terminally; 3 uppermost stamens markedly dissimilar, more or less rudimentary, the anthers distinctly bilobed, each lobe reniform and dehiscent the length of its outer margin; ovary linear, glabrous. Legume linear, turgid-quadrangular, up to 2 dm. long and 1 cm. wide, transversely multiseptate, tardily dehiscent along one margin (Missouri Botanical Garden, 2014).

S. spectabilis was present in Colombia as of 1832 (recorded as Cassia speciosa Kunth) (Don, 1832). Introduction of the species to the West Indies is uncertain but it was likely to have spread from its native South America some time ago. Specimens from Trinidad and Tobago were collected in 1862 (as Cassia spectabilis DC) (Royal Botanic Gardens Kew, 2003) and the species was being cultivated in the Royal Botanic Gardens of Trinidad by 1869 (as C. spectabilis) (Prestoe, 1870). By 1879 the species was known to occur in South Mexico, Costa Rica, West Indies and the northern parts of South America (as Cassia spectabilis DC) (Godman et al., 1879). The species must be a relatively recent introduction to Puerto Rico, as it was not included in Bello’s flora of Puerto Rico (Bello Espinosa, 1881). The species is considered by Irwin and Barneby (1982) as a cultivation escape in Trinidad and Tobago and both native and adventive to northern parts of the Orinoco basin, Venezuela, and while found in the Greater Antilles (Cuba, Jamaica, Hispaniola and Puerto Rico), it is “common only in Dominican Republic and probably nowhere truly autochthonous”. The lack of collections of S. spectabilis from the West Indies in the US National Herbarium may be indicative of the foreign origin of this species for this region. In Puerto Rico, this species is known from US collections dating from 1954 (US National Herbarium). However it is certainly much more widespread in Puerto Rico than what is currently reported in the literature or herbaria collections; recent fieldwork in Puerto Rico indicates that S. spectabilis is becoming widespread in the southern flanks of the Central mountain range in the area of Salinas and Villalba (Acevedo-Rodriguez, pers. comments). 

The species is thought to have been introduced to Africa by Indian sawmill operators or Europeans for firewood and live boundary marking, as a way to reverse deforestation, desertification and fuelwood shortages; however, the species has since invaded most forestry ecosystems, where it has outcompeted native tree species with its fast colonization and thicket establishments (Mungatana and Ahimbisibwe, 2010). The species was present in Tanzania prior to 1967, when it was intentionally introduced to Mahale Mountains National Park in order to create shade and later cultivated by farmers as living fences to prevent crop damage by animals. It is now recognized as an invasive alien species in parts of Kenya, Malawi, Tanzania and Uganda (Wakibara and Mnaya, 2002; Witt and Luke, 2017).

Soil drainage

• free

Soil reaction

• acid
• alkaline
• neutral
• very acid

Soil texture

• heavy
• light
• medium

Special soil tolerances

• shallow

S. spectabilis produces large quantities of seeds which can remain viable for up to three years and do not die easily, allowing the species to spread quickly, as pods burst and disburse seeds when they fall from the plant, and can spread further by water (PIER, 2014). The roots of the species are also known to germinate, and the tree coppices when cut down; thus in agroforestry, the species is propagated vegetatively via cuttings and stump plants (Irwin and Barneby, 1982; PIER, 2014).

S. spectabilis grows rapidly, can dominate other species in the wild, and in cultivated lands out-competes crops, causing a reduction in crop yield and reduction in native flora (Noordwijk et al., 2004).

• Proved invasive outside its native range
• Abundant in its native range
• Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
• Pioneering in disturbed areas
• Benefits from human association (i.e. it is a human commensal)
• Long lived
• Fast growing
• Has high reproductive potential
• Has propagules that can remain viable for more than one year
• Reproduces asexually

• Ecosystem change/ habitat alteration
• Monoculture formation
• Negatively impacts agriculture
• Reduced native biodiversity
• Threat to/ loss of endangered species
• Threat to/ loss of native species

• Competition - monopolizing resources
• Competition - shading
• Competition - smothering
• Rapid growth
• Rooting

• Highly likely to be transported internationally deliberately

S. spectabilis has been used for economic purposes. Its wood has been used for furniture, as lumber and construction materials, and to make wood carvings. In China and elsewhere the species is usually cultivated ornamentally, as its flowers are fragrant (Irwin and Barneby, 1982; Flora of China Editorial Committee, 2014). It has also been used as a hedgerow species in plantations and agricultural systems (Wakibara and Mnaya, 2002; Mungatana and Ahimbisibwe, 2010; PIER, 2014).

S. spectabilis is used in agroforestry as a shade tree and a living fence (Irwin and Barneby, 1982; Missouri Botanical Garden, 2014). The species is considered useful for fodder, mulch, fuelwood, and as a source of honey.