Ambrosia psilostachya (Perennial Ragweed) - photos and description

Male flowers in above photo.

Female flower in above photo. 

Female flower in above photo. 


Fruit in above photo.

Fruit in above photo. 

General: Perennial plants from rhizomes forming large colonies. Foliage is very hairy and rough to touch, light-green to greyish-green in colour.

Flowers: Flowers single-sexed on the same plant, the male flowers many, in a terminal spike; the female flowers below in axillary clusters (small whorls) along the stem. Male flowers pale yellow we measured a male flower at 3 mm diameter. Female flowers with a divided style, greenish, we measured a female flower at 2 mm long.

Fruit: Fruit more or less globose with a short beak, and with or without up to 5 small, stout tubercles, the tubercles growing in in a single row. Fruit measured to 3 mm diameter, tubercles measured to 0.5 mm long.

Leaves: Lanceolate to ovate in profile, mostly opposite, leaves once pinnatifid, lobes incised, having petioles below and sessile above, light-green to greyish-green in colour. Leaves pubescent with short hairs.

Height: Height listed in Budd's Flora to 90 cm, we measured plants to 52 cm tall.

Habitat: Open prairie, waste ground, roadsides.

Abundance: Listed as uncommon in Checklist of the Vascular Plants of Saskatchewan.

Origin: Introduced. However, I've read it's considered native to Manitoba and provinces east of Manitoba.

How to identify this species of Ambrosia: Rhizomatous, perennial, leaves not divided wholly to midrib (Taxonomic Reminder for Recognizing Saskatchewan Plants).

Similar species: This plant is very similar to Ambrosia artemisifolia (annual Ragweed).

Ambrosia psilostachya is rhizomatous, leaves once pinnatifid, and has leaves not divided wholly to midrib, while similar species Ambrosia artemisifolia has a taproot, lower leaves twice pinnatifid, and leaves divided to midrib.

When and where photographed: Photos were taken August 8th on prairie hillside, Qu'Appelle Valley, about 40 km northwest of Regina, SK, and September 5th on a weedy beach about 40 km northwest of our home in Regina, SK.