Peanut Butter Senna
Senna didymobotrya
NEMBA category
English: Peanut Butter Senna, Peanut Butter Cassia, Candle Bush, Oatmeal Cassia, Popcorn Senna, Candelabra Senna, African Senna, Cassia
Afrikaans: Kandelaarboom, Grondboontjiebotter-senna, Grondboontjiebotterkassia
Shona: Munwahuku
Misapplied or old scientific names: Cassia didymobotrya, Cassia nairobensis, Cassia verdickii
Senna didymobotrya, commonly known as Candle Bush or Peanut Butter Senna, is a fast-growing, evergreen shrub or small tree. It is easily identified by its large, pinnately compound leaves, distinctive upright, spike-like clusters of bright yellow flowers resembling candles, and flat, dark brown pods. When crushed, its leaves have a faint smell reminiscent of peanut butter.
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Origin:
Tropical Africa (eastern and central Africa, from Sudan south, and west to Cameroon).
Distinguishing features:
Large, pinnately compound leaves with numerous leaflets.
Upright, candle-like spikes of bright yellow flowers.
Flat, dark brown, bean-like pods.
Distinctive "peanut butter" smell when leaves are crushed.
Evergreen in warmer climates.
Overall appearance:
Senna didymobotrya grows as a robust, upright, and often multi-stemmed evergreen shrub or small tree. It has an open, somewhat spreading habit, forming a dense and striking display when in flower due to its prominent flower spikes.
Height:
Typically grows 2 to 4 metres tall, but can sometimes reach up to 5 metres in ideal conditions.
Width:
It can spread to a width of 1.5 to 3 metres.
Leaves:
The leaves are alternately arranged, large (up to 30 cm long), and pinnately compound, consisting of 8-18 pairs of oval to oblong leaflets, each 2-5 cm long and 1-2 cm wide. The leaflets are dark green above and paler underneath, often with a slightly hairy texture. When crushed, the leaves emit a characteristic, somewhat sweet, "peanut butter" or "popcorn" like aroma.
Flowers:
The flowers are bright yellow, pea-like, and relatively small (about 2-3 cm in diameter). They are produced in dense, erect, spike-like clusters (racemes) at the ends of branches, which can be up to 30 cm long, resembling candles or candelabras. The flower buds are often dark brown or black, providing a striking contrast with the bright yellow petals as they open from the base upwards. Senna didymobotrya flowers are hermaphroditic, containing both male and female reproductive parts, so it is not dioecious.
Flowering season:
In South Africa, it has a long flowering season, typically from late autumn through winter and spring (around May to October), but can flower almost year-round in warm, moist conditions. This makes it particularly noticeable when many other plants are not in bloom.
Fruits:
The fruits are flat, straight or slightly curved pods, 5-10 cm long and about 1.5-2.5 cm wide. They are initially green, turning dark brown to almost black as they mature, and are typically covered with fine hairs. The pods contain several seeds and eventually split open to release them.
Seeds:
The seeds are flat, oval to kidney-shaped, dark brown to black, and about 5-8 mm long. Each pod can contain numerous seeds (up to 15-20), which are viable and contribute to its spread.
Bark:
The bark on young stems is green and often slightly hairy. As the plant matures, the bark on the main stem becomes greyish-brown and can be somewhat rough or furrowed.
Thorns:
This plant does not have thorns.
Wood:
The wood is relatively soft and brittle. It is not typically used for timber or commercial purposes.
Roots:
It has a fibrous root system that allows it to establish quickly and compete effectively.
Soil type:
It is adaptable to a wide range of soil types, including sandy, loamy, and clay soils, provided they are well-draining. It can tolerate poor soil conditions but thrives in moist, fertile soils.
Aspect:
Prefers full sun to partial shade. It is not tolerant of severe or prolonged frost. It thrives in warm, moist, high-rainfall areas.
Edibility:
All parts of Senna didymobotrya are generally considered non-edible and potentially toxic. The seeds are particularly dangerous.
Toxicity:
All parts of Senna didymobotrya contain anthraquinone glycosides, which are purgative (laxative) and can be toxic if ingested in large quantities, particularly the seeds. Symptoms of poisoning in humans or livestock can include severe gastrointestinal upset (nausea, vomiting, diarrhoea, abdominal pain).
Uses:
Primarily cultivated as an ornamental plant in gardens due to its showy, long-lasting yellow flowers, especially during winter when colour is scarce. It is also used in traditional African medicine for various ailments, though extreme caution is necessary due to its toxicity.
Ecology:
Although native to parts of tropical Africa, Senna didymobotrya can become invasive in other areas of South Africa, particularly where conditions are favourable (moist, disturbed sites). Its invasive impacts include:
Displacement of indigenous vegetation: It can form dense stands, especially in disturbed areas, forest margins, roadsides, and along watercourses, outcompeting native plants for light, water, and nutrients.
Habitat alteration: Its rapid growth and dense canopy can alter light conditions and reduce biodiversity in invaded areas.
Prolific seed production: It produces numerous viable seeds that are readily dispersed, contributing to its spread.
Potential toxicity: Its toxic nature can pose a risk to grazing animals.
Distribution and habitat:
In South Africa, Senna didymobotrya is considered an alien invasive, even though it is indigenous to certain tropical parts of the continent. It is particularly invasive in the higher rainfall, warmer regions. It is found in provinces such as KwaZulu-Natal, Mpumalanga, Limpopo, Eastern Cape, and Gauteng. It commonly invades roadsides, disturbed areas, forest margins, woodlands, riparian zones (along watercourses), and abandoned fields.
Derivation of name:
The genus name Senna is derived from the Arabic word "sana," which refers to species of Cassia (the genus it was previously part of) known for their medicinal properties.
The species name didymobotrya comes from Greek: "didymos" (twin or double) and "botrys" (a cluster or raceme), likely referring to the arrangement of its flower spikes, though it might more accurately refer to its paired leaflets.
Common names like "Candle Bush" refer to the distinctive upright, candle-like flower spikes. "Peanut Butter Senna" describes the peculiar smell of its crushed leaves.
Historical aspects:
Senna didymobotrya has been cultivated as an ornamental plant for many years due to its striking winter flowers. Its easy cultivation and attractive appearance led to its widespread planting in gardens. However, its aggressive growth and ability to escape cultivation have led to its classification as an environmental weed in areas outside its natural ecological distribution.
NEMBA Status:
1b in Eastern Cape, KwaZulu-Natal, Limpop, Mpumalanga and Western Cape. b. Not listed elsewhere.
Interesting facts:
Fancy a sniff? If you gently crush a leaf of the Candle Bush, you might be surprised by a faint smell of peanut butter or even popcorn! It's one of its coolest party tricks.
This plant is like a natural candelabra! Its bright yellow flowers stand upright in long spikes, making it look like a giant candle holder, especially when they bloom in the cooler months.
While it's pretty, don't let it fool you – all parts of this plant are considered toxic, especially its seeds. So, no taste tests, please!
This plant is a bit of a chameleon when it comes to being "native." While it's originally from parts of Africa, it acts like an invasive alien in other areas of South Africa, spreading where it's not wanted.
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