Stylosanthes humilis is an annual herbaceous legume 50-70 cm tall. It reproduces by seeds. The stem may be erect or prostrate, hairy, and branching.
It can be identified by its short, hairy stems and its inflorescence comprising hirsute spikes that contain bright yellow flowers.
Townsville Stylo Classification
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Tracheophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Fabales
- Family: Fabaceae
- Genus: Stylosanthes
- Species: Stylosanthes humilis
- Varieties: Andre, Cerro, Tanzania, and Stylo
- Common Names: Townsville lucerne, Wild lucerne, Annual stylo, and Long-beak pencil flower
Nativity and Distribution
Townsville stylo is native to the Caribbean, Central America, and South America. It is now widespread in other places globally including:
- North Australia
- Kenya
- Tanzania
- India
- Malaysia
- Philippines
Physical Characteristics
- Leaves: Trifoliate leaves with lanceolate or elliptical leaflets
- Fruits: 2-segmented hairy articulated pod
- Stems: Herbaceous. It can grow up to 70 cm
- Flowers: Small bright yellow flowers on hirsute peaks
- Roots: A tap root system (can develop adventitious roots)
Stylosanthes humilis is a low-growing annual (sometimes perennial) legume that can be upright (50-70 cm) or prostrate. It is easily recognized by its short, hairy stems and its inflorescence comprising hirsute spikes that contain bright yellow flowers.
Stems are narrow and heavily branched, with hair on one side and scattered bristles. They may be erect or prostrate when growing under high moisture conditions. The leaves are trifoliate with narrow glabrous leaflets, the terminal about 3.5mm wide and 15mm long.
The inflorescence is arranged on short and ovoid spike-like racemes. Each spike comprises 3-15 pea-shaped bright yellow flowers, each 3-4mm wide. The flowers have a short-day flowering response which means they bloom best on shorter days.
Flowering occurs in the warm months and during rainfall but is negatively affected by latitude and night temperature.
The seeds are yellowish to brown, typically elliptical with a distinct hook.
Reproduction, Dispersal, and Life Cycle
- Life Cycle: Annual (sometimes perennial)
- Seeds: A single plant can produce 1,000 to 3,000 seeds
- Climate: Tropical and lower latitude subtropical regions
- Dispersal: Animals, water, and contaminated equipment
Stylosanthes humilis behaves as an annual but can also act as a perennial in regions where it is heavily grazed. It reproduces by seeds.
One isolated plant can produce between 1,000 to 3,000 seeds. The seeds have hooks that enable them to attach to animal fur, getting dispersed to far locations. They are also spread through animal waste, water, and contaminated tools and machinery.
Townsville stylo seeds can easily germinate in shallow soil (up to 3 cm). Unlike the parent plant, the seeds can survive frost and fire. A great flush of germination is generally observed after a fire once the seed becomes softened.
Similar Plants
- Stylosanthes hamata
- Stylosanthes fruticosa
- Stylosanthes biflora
Uses
- It is a valuable forage legume used for grazing livestock and is preserved as hay for future use.
- As a nitrogen-fixing legume, it is valuable in agricultural systems for enhancing soil fertility.
- It is used as a cover crop to suppress weeds and reduce soil compaction.
- The stems and leaves produce a distinct secretion used to control the Bovine tick (Rhipicephalus microplus).
Impact on Farms and Environment
S. humilis is a valuable fodder and nitrogen-fixing legume, providing numerous benefits for mixed agricultural systems.
However, Townsville lucerne like many others in its species has been observed to acidify light soils by leaching unused nitrates back into the soil.
Additionally, due to its aggressive growth, Townsville stylo is considered a weed in many agricultural areas.
It is also susceptible to diseases such as anthracnose disease, bacterial wilt, and blight which can be a potential threat in cropping systems.
Control
- Mechanical control: Hand pulling, mowing, and tillage
- Cultural control: Grazing
- Chemical control: Herbicides like 2,4-D and glyphosate
The best form of weed management is prevention. Since Townsville stylo is not a significant weed, it is possible to prevent establishment through monitoring and quick deployment of control measures.
If prevention is no longer possible, hand pulling can be effective for small isolated infestations.
Regular mowing can prevent seeding but it may not eradicate the plant as it can regrow from the roots. In larger areas, repeated tillage will disrupt the soil and uproot the plants, providing faster and more effective control.
Grazing can help control the weeds in rangelands if done during the early growth stages. However, if left to establish, it can survive heavy grazing, making this strategy less effective.
Chemical herbicides containing 2,4-D or glyphosate are effective in eradicating widespread infestations. When using herbicides, always read the label and follow the application instructions for the best results.
Lead Editor for Insight Weeds.