Senna pendula is a species of flowering plant in the legume family, Fabaceae, native to South America. It is widely cultivated as an ornamental plant for its attractive yellow flowers, but has also become a significant invasive species in many subtropical and tropical regions around the world.
Taxonomy
- Kingdom: Plantae
- Clade: Tracheophytes
- Clade: Angiosperms
- Clade: Eudicots
- Clade: Rosids
- Order: Fabales
- Family: Fabaceae (Leguminosae)
- Subfamily: Caesalpinioideae (formerly included in Mimosoideae and Papilionoideae, but now recognized as a distinct subfamily within Fabaceae s.l.)
- Tribe: Cassieae
- Genus: Senna
- Species: S. pendula
The genus Senna comprises a large group of shrubs, herbs, and trees. Senna pendula was formerly known by several synonyms, including Cassia coluteoides, Cassia bicapsularis (misapplied), and Cassia pendula. The epithet "pendula" refers to its often drooping or pendulous branches.
Description
Senna pendula is a fast-growing, evergreen to semi-deciduous shrub or small tree, typically reaching 2–4 meters (6–13 feet) in height, though it can climb higher into other vegetation.
- Leaves: The leaves are compound and pinnate, 7–12 cm long, with 3–6 (usually 4–5) pairs of obovate or elliptic leaflets. The leaflets are dark green, smooth, and have a distinctive small gland between the lowest pair of leaflets on the petiole.
- Flowers: Showy, bright golden-yellow flowers are produced in profusion, often from autumn through winter or early spring, giving rise to common names like "Christmas Senna" or "Easter Cassia" depending on the flowering period in different regions. The flowers are approximately 2–3 cm across and borne in axillary racemes or terminal panicles.
- Fruit: The fruit is a cylindrical pod, initially green, ripening to a dark brown or black. The pods are 10–18 cm long and about 1 cm wide, containing numerous hard, flattened seeds.
- Stems: Stems can be somewhat woody, often scrambling or arching, sometimes forming dense thickets.
Distribution and Habitat
Senna pendula is native to a broad region of South America, including Brazil, Argentina, Paraguay, and Uruguay. It typically grows in disturbed areas, forest margins, riparian zones, and along roadsides.
Cultivation and Uses
Senna pendula is widely cultivated as an ornamental plant in tropical, subtropical, and warm temperate regions. Its appeal lies in its vibrant floral display, relatively easy cultivation, and tolerance to various soil conditions. It is used in gardens, parks, and as a screening plant.
Invasive Species Status
Despite its ornamental value, Senna pendula has become a significant environmental weed and invasive species in many parts of the world, particularly in Australia, New Zealand, South Africa, and parts of the United States (e.g., Florida, California, Hawaii).
- Environmental Impact: It forms dense monocultures, outcompeting and displacing native vegetation, altering natural ecosystems, and reducing biodiversity. Its aggressive growth can smother native shrubs and trees.
- Spread: The plant produces abundant seeds that are dispersed by birds (which are attracted to the pods), water, and human activities. It can also spread vegetatively through layering.
- Management: Management often involves physical removal (hand-pulling, cutting), chemical control (herbicides), and biological control where appropriate.
Toxicity
All parts of Senna pendula, particularly the seeds, are considered toxic if ingested. They contain anthraquinone glycosides, which can cause gastrointestinal upset, nausea, vomiting, and diarrhea in humans and livestock. Skin contact with the plant sap can also cause dermatitis in sensitive individuals.
Common Names
- Christmas Senna
- Easter Cassia
- Climbing Senna
- Winter Senna
- Golden Senna
- Butterfly Bush (though this name is more commonly applied to Buddleja davidii)