Heteropogon contortus is a perennial grass that grows 0.5-1.5m tall. It reproduces by seeds and vegetative transplants.
It is easily identified by its blue to green-blue leaves and stems, as well as its dark brown awns that twist together at seed maturity.
Spear Grass Classification
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Monocotyledonae
- Order: Cyperales
- Family: Poaceae
- Genus: Heteropogon
- Species: Heteropogon contortus
- Common Names: Speargrass, Common spear grass, Black spear grass, Bunch spear grass, Tangle grass, Tanglehead, and Twisted beardgrass.
Nativity and Distribution
Spear grass is native to Africa, Southern Asia, Australia, Oceania, and Southwestern Europe. Today, it is naturalized in other regions globally such as:
- Southern United States
- Central and Southern America
- East Asia
- Caribbean
Physical Characteristics
- Leaves: Flat or folded, green to bluish-green, 10-30 cm long x 2-8 mm wide
- Stems: Slender, tufted, up to 1.5 m tall
- Flowers: Long raceme borne with a single or pair of flat green spikelets
- Roots: Fibrous root system
Heteropogon contortus is a perennial tufted grass 0.5-1.5m tall. It reproduces by seeds and vegetative transplants.
The grass is easily identified by its blue to green-blue leaves and stems as well as its dark brown awns that twist together at seed maturity.
Culms are slender, typically geniculate at the base, erect at upper levels, and often branched, especially during flowering. The tufted stems are about 0.5-1.5m tall.
Bluish to bluish-green in color, the leaves are either glabrous or with few fine hairs. The blades are folded when young and flat at maturity, about 3-30 cm long and 3-8mm wide.
Spear grass produces a 3-8 cm raceme of narrowly cylindrical homogamous spikelets. The sterile spikelets are awnless and located at the base of the raceme. The bisexual spikelets are awned and borne at the apex. As the seeds mature, the long awns (6-10 cm) tips twist together, a distinct trait of the spear grass.
The caryopsis is cylindrical, grooved, whitish, and 3.5-4.5 mm long.
Reproduction, Dispersal, and Life Cycle
- Life Cycle: Perennial
- Seeds: A single plant can produce 3,000 seeds
- Climate: Tropical and subtropical climates
- Dispersal: Attachment to fur and clothing
H. contortus behaves as a perennial grass and thrives in tropical and subtropical climates with distinct wet and dry seasons. It has a lifespan of less than five years.
The grass is a prolific seed producer with a single plant producing up to 3,000 seeds. Their harpoon-like barbs aid them in attaching to animal fur, feathers, and clothing, dispersing them to new areas.
When the moisture conditions are right, the awns and sharp tips twist, planting the seeds in the soil. Germination occurs between 5-7 days. Seed dormancy is 6 months with a lower germination rate.
Similar Plants
- Chrysopogon fulvus
- Bothriochloa pertusa
- Sorghastrum nutans
Uses
- It is used as a summer pasture and forage for livestock.
- It is grown as an ornamental plant for its interesting seed head.
- The grass is used for thatching, matting, and stuffing pad floors.
- It is used to make remedies for burns and wounds by the Zulu community in South Africa.
- The grass is used in land reclamation, weed suppression, soil erosion, and carbon sequestration efforts.
Impact on Farms and Environment
Heteropogon contortus is highly regarded for its land reclamation ecosystem restoration abilities. Tropical vegetable farmers in Hawaii rely on the grass for weed suppression, improving soil structure, and increasing biodiversity.
The grass has also been recommended for soil erosion control along roadsides, construction sites, and other disturbed sites in the U.S.
H. contortus can also improve biodiversity in various ecosystems, including riparian areas. For instance, it is a favorite pollinator plant for bees.
However, spear grass has also been declared as an invasive weed in some regions in Asia and America. It is a common weed of crop farms, grasslands, pathways, and roadsides. Its ability to withstand burning and light to medium grazing can make eradication efforts difficult.
The seed’s harpoon-like attachments can become embedded in the wool and skin of sheep. This has led to the closure of some wool industries in parts of Australia, negatively impacting livelihoods.
It is also a collateral host for downy mildew in sorghum and maize.
Control
- Cultural control: Heavy grazing can help eradicate the grass.
- Chemical control: Apply glyphosate herbicide for complete removal.
Spear grass is intolerant of continuous heavy grazing and this cultural practice can be used to eradicate it in the early wet season.
Glyphosate is highly recommended for lasting and more effective control against Heteropogon contortus.
Lead Editor for Insight Weeds.