What Does It Look Like?
What is it?
Lacy Ragweed (Ambrosia tenuifolia) is an erect perennial herb to 750 mm high, stoloniferous (with slender stems growing horizontal or trailing along the ground, producing roots and erect shoots at its nodes). Stems with bristly hairy, simple or sparsely branched stems, woody towards the base. The leaves are 30–80 mm long and 40–50 mm wide, arranged alternate or opposite on the stem, rhombic in outline, are grey-green and are bipinnatisect (twice-divided into narrow segments), segments mostly less than 1.5 mm wide, giving a lacy fern-like appearance, leaves . Leaf surfaces greyish from a covering of long white hairs, leaf stalk (petiole) to 20 mm long.
Flowers are greenish-white. Two types of flower-heads are borne on the same plant. Male flower-heads are many, comprising 12 tiny male florets, and are grouped into cup-shaped heads, about 2.5 mm in diameter, in spikes at the end of the stems, a ring of fused bracts enclosing the florets. Female flower-heads are fewer and are in 1-flowered heads, solitary or in small clusters, borne between the stems and bases of the upper leaves. Each female flower produces a seed with many seeds produced on a flower-head.
The fruits or 'seeds' (cypselas) are bluntly top-shaped, woody, 3–4 mm long, with a pointed beak, slightly ribbed, surrounded by 4 to 5 short projections (Parsons & Cuthbertson 2001), short spines above, . Flowers spring and summer.
For further information and assistance with identification of Lacy Ragweed contact the herbarium in your state or territory.
Growth form (weed type/habit)
Where it currently grows? Preferred habitat
Lacy Ragweed grows in subhumid temperate regions, in lighter soils in open areas, occurring as a weed of roadsides, railway reserves, sand dunes, cultivated fields, degraded pastures and waste areas (Parsons & Cuthbertson 2001).
Are there similar species?
Lacy Ragweed is not readily mistaken for other species.