The most commonly affected hosts occur in the families Acanthaceae, Convolvulaceae, Euphorbiaceae, Fabaceae and Solanaceae ( Parker and Riches, 1993). The main economic host is cowpea, with tobacco and sweet potato also affected very locally. gesnerioides, as a species, has a wide host range, including annual, perennial and woody species, mainly in Dicotyledonae but also some grass species. gesnerioides also differs from most other Striga species in developing a substantial haustorium at least several millimetres across, about 1 cm on tobacco and often up to 3-4 cm in diameter on cowpea. Seed production per plant was estimated to be over 60,000 ( Hartman and Tanimonure, 1991). asiatica (see Musselman and Parker, 1981). The capsule, up to 5 mm long, develops several hundred minute seeds about 0.25 mm long, not readily distinguishable from those of S. Flower colour in forms attacking cowpea is usually mauve but occasionally white, whereas in other forms it may be reddish, purple or even yellow. Flowers, generally in opposite pairs, subtended by bracts 4-6 mm long, are sessile with a tubular calyx, also 4-6 mm long with five ribs and corolla 5-15 mm long with corolla lobes expanding to about 5 mm across. Much of the shoot comprises the spike-like inflorescence. In vigorous plants, as on cowpea, the stems branch mainly below the soil and emerge as a cluster of generally unbranched, fleshy, erect shoots 10-20 cm high, with scale leaves only a few millimetres long ( Parker and Riches, 1993). gesnerioides differs markedly from most other Striga species, in being totally parasitic, without expanded leaves and with a pale-green or yellowish colour.
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