Monday, April 26, 2010

A Pretty Pest

Common Toadflax, Linaria vulgaris

Rare in the rest of Ireland, the pretty Common Toadflax (Linaria vulgaris) is frequently spotted in the South to Southeast of the country. Producing its yellow flowers from June to October, it can be found on roadsides, waste ground, grass banks and cultivated fields growing to a height of 60 cm. Its status as an Irish native is questionable, however it does help to support long-tongued pollinators such as Bombus pascuorum and B. hortorum by the provision of valuable nectar (Corbet et al., 2001 Annals of Botany 87 pp. 219-232). Taxonomically, L. vulgaris was traditionally placed in the family Scrophulariaceae. Recent phylogenetic analysis of DNA regions from members of the family now places the genus Lniaria within the Plantaginaceae (Albach et al., 2005 American Journal of Botany 92 pp. 297–315).

L. vulgaris is used in traditional medicine as a laxative, as well as for the treatment of inflammation of the bladder, skin rashes and haemorrhoids. Its perceived activity is due to the presence of iridoid glucosides (such as antirrinoside and procumbide) in the stem, leaves and roots of the plant (Ilieva et al., 1992 Phytochemistry 31 pp. 1040-1041).

Unfortunately, what is seen as an attractive margin wildflower by some, has become a pest to others. L. vulgaris was introduced to the USA as an ornamental garden plant, but soon escaped into the wild and was recognized as a major agricultural weed in 1758 by the botanist John Bartram (Mack, 2003 Annals of the Missouri Botanical Garden 90, 77–90). Bartram stated that “neither the spade, plough nor hoe can eradicate it, when it is spread to a pasture”, undoubtedly due to the extensive creeping root system of the plant. The problem persist today, however the introduction of the weevil Mecinus janthinus as a biological control agent into both the USA and Canada has helped to control L. vulgaris populations (McClay and Hughes, 2007 Biological Control 40 pp. 405-410).

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