Abstract

Achillea wilhelmsii C. Koch (Asteraceae) is a wild herb widely disturbed in Iran and known locally as yarrow. This plant is an important medicinal plant and it has been used for its analgesic, antiphlogistic, antispasmodic, and antibacterial effects in Iranian folk medicine. Field surveys revealed infestations of yarrow broomrape, Orobanche purpurea Jacq., on A. wilhelmsii plants in two locations in province of Zanjan (Zanjan, 36°37′19.85″ N, 48°27′16.87″ E, 1,707.4 m elevation, and Qolabar, 36°19′19.85″ N, 48°19′16.41″ E, 1,663.9 m elevation) in northwestern Iran in May 2012. The annual mean air temperature and the average maximum and minimum air temperatures were 11, 18, and 4°C, respectively. The annual mean precipitation was 298 mm. The infestation of A. wilhelmsii was confirmed by verifying the attachment of the yarrow broomrape to the A. wilhelmsii roots. Broomrape plant heights were between 24 and 37 cm. The stems were erect, unbranched, slender, and swollen near the base at contact with host, 0.5 to 10 mm diameter. The leaves were reduced to scale or bracts up to 10 to 15 mm long. The flowers were in dense terminal spikes, usually restricted to the top third or half of the shoot. There was one bract and two bracteoles surrounding each flower. The bracts measured 7 to 10 mm, had ovate lanceolates shorter than the calyces, and lanceolate bracteoles were 5 to 10 mm. The calyces were gamosepalous, entire, and whitish. Corollas were 13 to 18 mm long, and were dull bluish-purple with dark veins, suffused with whitish-yellow at the base. The upper part was slightly curved forwards. Stamens were epipetalous, inserted 4 to 7 mm above the corolla base, with filaments glabrous. The anthers were glabrous along sutures. Stigma lobes were white. Fruit was an oval capsule, 0.9 to 10 mm. Botanists at the College of Agriculture of Zanjan University confirmed the identity of O. purpurea. A. millefolium has been reported as a host plant for yarrow broomrape (1,2). However, to our knowledge, this is the first report of yarrow broomrape on A. wilhelmsii in Iran. Since production and farming of A. wilhelmsii as a medicinal plant has recently started on a commercial scale in Iran, the parasite weed could pose a serious threat to production of this plant.