What Does It Look Like?
What is it?
Innocent Weed (Cenchrus longispinus) is an upright or spreading, leggy, sparse, annual, biannual or short-lived grass usually growing up to 60 cm tall, but sometimes reaching 90 cm in height. The narrow leaf blades are 3–20 cm long and 3–8 mm wide and are mostly hairless, while the leaf sheaths are hairless or sparsely hairy and often have a reddish or purplish tinge. Where the leaf sheath meets the leaf blade there is a fringe of small hairs 0.5–2 mm long.
The flower head or inflorescence is a spike 3–7 cm long, the axis flattened and flexuose. The seed head is often partially enclosed within the upper-most leaf sheath are borne on stalks 1–5 mm long, contain a cluster of 8–18 flower spikelets, and each flower spikelet contains 1-3 flowers, each usually produces a single seed.
The fruit (seed) heads are burr-like structures (burrs) that are 3–12 mm across, each bearing usually 40–70 sharp spines that are 3.5–7 mm long and relatively slender. The 'burrs' are a reddish or purplish-green colour when young but turn straw-coloured or brown as they mature and usually detach from the stem. The smooth seeds are 2–4 mm long and 2–3 mm wide and are egg-shaped, but flattened on one side, and remain well hidden within the burrs (Navie 2004).
For further information and assistance with identification of Innocent Weed, contact the herbarium in your state or territory.
Red, Purple, Green, White, Brown
Growth form (weed type/habit)
Where it currently grows? Preferred habitat
Innocent Weed is found mostly in sub-tropical, semi-arid, and warmer temperate environments, and is a weed of disturbed sites, waste areas, roadsides, pastures and cultivation and disturbance. It prefers sandy well drained soils (Navie 2004).
Are there similar species?
Innocent Weed is very similar to another species known as Spiny Burrgrass (Cenchrus spinifex) [as Cenchrus incertus], Mossman River Grass (Cenchrus echinatus) and Buffel Grass (Cenchrus ciliaris). Innocent Weed (Cenchrus longispinus) can be distinguished from these by spiny 'burrs' which are produced on its seed head. These 'burrs' have short stalks and have several rows of larger flattened spines, usually with 40–70 spines in total. In contrast the burrs on Spiny Burrgrass (Cenchrus spinifex) [as Cenchrus incertus] while also having several rows of larger flattened spines, usually with only 8–25 spines in total. The burrs on Mossman River grass (Cenchrus echinatus) do not have stalks and only have one row of larger flattened spines. Buffel Grass (Cenchrus ciliaris) has seed heads that do not produce spiny 'burrs'. Instead, its seed heads bear flower spikelet clusters that have numerous long stiff bristles (Navie 2004).