Striga spp.

Name and classification

Striga Lour.
Family Scrophulariaceae

Common names

witchweed

Disseminule

seed

Description

Note: This description is primarily based on the morphology of seven species.

Fruit a loculicidal capsule with numerous seeds. Seeds elliptic, ovate, oblong, occasionally D-shaped, triangular, rhombic, or irregular; often twisted or angled from crowding or position in capsule; tiny, dustlike, 0.2–0.6 mm long, 0.1–0.3 wide and thick. Orange to golden-brown, light to dark brown, or gray to blackish; sometimes sparkling with colored light at high magnification. Surface glabrous, with prominent often ropelike longitudinal or diagonal reticulations that sometimes appear as closely spaced ridges rather than reticulations and are often twisted in appearance. Embryo linear; endosperm present.

Identification considerations

It may be difficult to differentiate seeds among Striga species. Compare with very small seeds of other parasitic plants on the federal noxious weed list:

Aeginetia spp.

Orobanche and Phelipanche spp.

Distribution

Africa, Asia, Australia, United States

native range: Old World tropics to South Africa

General information

Striga comprises ca. 40 species, 28 of which are found in Africa. These plants are annual root hemiparasites, the seeds germinating in response to host root exudates. The damage occurs underground. Striga most often attack grasses such as corn, rice and sorghum, causing stunting or total loss of the host crop. Three species, S. asiatica (L.) Kuntz (=S. lutea Lour.), S. gesnerioides (Willd.) Vatke, and S. hermonthica (Delile) Benth., cause the most damage to tropical agriculture. Striga asiatica is the most widespread in the world. Other species may be important locally. When these plants were discovered in the U.S. in North Carolina and South Carolina, a federal witchweed program was established to prevent spread and eliminate these parasites.

Striga asiatica (L.) Kuntz. seeds

Striga asiatica (L.) Kuntz. seeds

Striga asiatica seeds, detail

Striga asiatica seeds, detail

Striga asiatica A, seed; B, longitudinal section of seed showing embryo; C, transection of seed; drawing by Lynda E. Chandler

Striga asiatica A, seed; B, longitudinal section of seed showing embryo; C, transection of seed; drawing by Lynda E. Chandler

Striga aspera (Willd.) Benth. seeds

Striga aspera (Willd.) Benth. seeds

Striga aspera seeds, detail

Striga aspera seeds, detail

Striga euphrasioides Benth. seeds

Striga euphrasioides Benth. seeds

Striga euphrasioides seeds, detail

Striga euphrasioides seeds, detail

Striga forbesii Benth. seeds

Striga forbesii Benth. seeds

Striga forbesii seeds, detail

Striga forbesii seeds, detail

Striga forbesii Benth. seeds

Striga forbesii Benth. seeds

Striga gesnerioides seeds, detail

Striga gesnerioides seeds, detail

Striga hermonthica (Delile) Benth. seeds

Striga hermonthica (Delile) Benth. seeds

Striga hermonthica seeds, detail

Striga hermonthica seeds, detail