Senna spectabilis
(whitebark senna)

Pictures

Picture	Title	Caption	Copyright
Title Trees Caption Stand in secondary growth forest. Copyright ©Rafael T. Cadiz	Trees	Stand in secondary growth forest.	©Rafael T. Cadiz
Title Branches Caption Copyright ©Rafael T. Cadiz	Branches		©Rafael T. Cadiz
Title Leaves Caption Copyright ©Rafael T. Cadiz	Leaves		©Rafael T. Cadiz

Identity

Preferred Scientific Name

• Senna spectabilis (DC.) H. S. Irwin & Barneby

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)

Summary of Invasiveness

S. spectabilis is a medium to large tree from tropical America, listed in the Global Compendium of Weeds as an ‘environmental weed’, ‘garden thug’, and ‘naturalised weed’ (Randall, 2012). The species is extremely fast-growing, flowers and sets seed profusely, and re-sprouts readily when cut (Mungatana and Ahimbisibwe, 2010). In Australia it is considered naturalized, has been recorded as a weed of the natural environment and an escape from cultivation, and is labelled an invasive species, indicating its high negative impact on the environment due to its ability to spread rapidly and often create monocultures (Randall, 2007). In Uganda, the species is considered an invasive alien species with high risk to the native flora (Mungatana and Ahimbisibwe, 2010). In Singapore S. spectabilis has been identified as a casual, spontaneous exotic species that survives outside cultivation but does not form self-replacing populations, and relies on repeated introductions or limited asexual reproduction for persistence (Chong et al., 2009). The species is a cultivation escape in Trinidad and Tobago (Irwin and Barneby, 1982) and is considered an invasive species in Cuba (Oviedo-Prieto et al., 2012).

Taxonomic Tree

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

Notes on Taxonomy and Nomenclature

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).

Description

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).

Plant Type

Distribution

S. spectabilis is generally considered to be native to South America and introduced to Central America and the West Indies, eventually naturalizing in many parts, but its pre-Columbian range of dispersal is obscure (Irwin and Barneby, 1982; Acevedo-Rodriguez and Strong, 2012; PIER, 2014). S. spectabilis var. spectabilis and var. excelsa have differing distribution ranges. Whereas var. spectabilis is native to parts of Colombia, Venezuela, parts of southeastern Bolivia, north Argentina, and Paraguay and discontinuously widespread in parts of tropical North and South America, var. excelsa is widespread primarily in interior east tropical Brazil and coastal Ecuador, although to be expected elsewhere (Irwin and Barneby, 1982). 

In Micronesia, PIER (2014) reports the species as invasive to Nuku Hiva Island, citing Wagner and Lorence’s Flora of the Marquesas database; however Wagner and Lorence (2014) do not specify its invasiveness in the database. PIER (2014) lists the species as an invasive introduction to Singapore, whereas Chong et al. (2009) report it as a casual introduction to the island that has not yet become invasive.

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

History of Introduction and Spread

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 both Tanzania and Uganda (Wakibara and Mnaya, 2002).

Risk of Introduction

Risk of introduction for this species is very high. The species received a PIER Risk Assessment Score of 11 [a score greater than 6 = reject the plant for import (Australia) and likely to be of high risk (Pacific and Florida, USA)], indicating that it poses a high risk of becoming a serious pest based on current evidence. The species is fast-growing and spreads profusely, traits that maximize its capability to compete with cash crops and native flora (Llamas, 2003). It also forms dense thickets where it spreads, at the expense of other species (PIER, 2014). 

Snapp and Pound (2008) conclude: “this agroforestry species acts as a highly effective weed species and has traits that maximize its ability to compete with cash crops. Promotion of S. spectabilis based on tremendous biomass potential was an insufficient criterion and may have been based on performance-on-research station trials, where soils of high organic matter may not have been representative of smallholder farm environments. Biological review of S. spectabilis and testing on farms revealed the highly competitive nature of this species and its unsuitability as an intercrop species”.

Habitat

In Brazil and Ecuador the species grows in coastal areas (Irwin and Barneby, 1982; Missouri Botanical Garden, 2014). In Bolivia the species can be found in both the lowlands and the Andes, in habitats ranging from rain forest, semi-deciduous and dry forest, montane forest, and dry valleys (Missouri Botanical Garden, 2014). In Peru, the species occurs in disturbed habitats, ranging from Amazonian to coastal areas. In Nicaragua the species is known to grow in wet and dry seasonal forests and secondary forests. In Paraguay the species has been observed in closed forests (Missouri Botanical Garden, 2014). The species was originally introduced to parts of Africa as an intercrop/hedgerow species in plantations and cultivated areas (Wakibara and Mnaya, 2002; Mungatana and Ahimbisibwe, 2010).

Habitat List

Hosts/Species Affected

Agroforestry experiments in Kenya showed that while S. spectabilis is useful as hedges for cropping systems, if grown in semi-arid conditions S. spectabilis will out-compete crops for water uptake and suppress crop yields; in the cases recorded, grain yields of maize grown with S. spectabilis or Leucaena leucocephala were reduced by between 39% and 95% (Noordwijk et al., 2004).

Biology and Ecology

Genetics

Chromosome count for the species is 2n=14 (IPCN Chromosome Reports, 2014). 

Environmental Requirements

S. spectabilis requires full sunlight, as it does not appear to establish under full canopy forest (PIER, 2014). It requires well-drained soil, has low tolerance for aerosol salt, and can tolerate a range of soil types including moist, clay, sand, loam, slightly alkaline, and acidic soils, reportedly able to flourish even in poor, black cotton soils and can reportedly adapt to alkaline soils (Mungatana and Ahimbisibwe, 2010; Gillman and Watson, 2011). 

In Ecuador the species has been reported to occur at 0-500 m (Missouri Botanical Garden, 2014). The species occurs at elevations of 0-2000 m in both Antioquia (Colombia) and Bolivia, and in Antioquia it tolerates environments including “Bosque Húmedo Premontano (premontane humid forest) (bh-PM), Bosque Húmedo Tropical (tropical humid forest) (bh-T), and Bosque seco Tropical (tropical dry forest) (bs-t)” (Flora of Bolivia Editorial Committee, 2014; Missouri Botanical Garden, 2014). The species grows at altitudes of 0-500 m in Peru, between 0 and 1000 m altitudes in Panama, and between 0 and 1300 m in Nicaragua (Missouri Botanical Garden, 2014).

Climate

Latitude/Altitude Ranges

Air Temperature

Rainfall

Rainfall Regime

Soil Tolerances

Soil drainage

• free

Soil reaction

• acid
• alkaline
• neutral
• very acid

Soil texture

• heavy
• light
• medium

Special soil tolerances

• shallow

Means of Movement and Dispersal

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).

Pathway Causes

Pathway Vectors

Impact Summary

Environmental Impact

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).

Risk and Impact Factors

• 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

Uses

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.

Uses List

Animal feed, fodder, forage

• Fodder/animal feed

Environmental

• Agroforestry
• Boundary, barrier or support

Fuels

• Fuelwood

Human food and beverage

• Honey/honey flora

Materials

• Wood/timber

Wood Products

Furniture

Roundwood

• Building poles
• Posts

Woodware

• Turnery
• Wood carvings

References

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Links to Websites

Contributors

02/04/2014 Original text by:

Marianne Jennifer Datiles, Department of Botany-Smithsonian NMNH, Washington DC, USA

Pedro Acevedo-Rodríguez, Department of Botany-Smithsonian NMNH, Washington DC, USA

Distribution Maps