ABSTRACT
The wide geographic distribution of species of this genus may be interpreted as evidence of an ancient origin of the genus. Stem nematode, stem and bulb nematode 1 A total of 13 nominal species have been synonymized. Most species were generally characterized and distinguished from other nominal stem nematode species by certain host preferences. Stem nematodes in, for example, flower bulbs and seeds of lucerne, field beans, onions, and other Allium species are on the list of quarantine organisms of many countries all over the world. Stem nematodes were found in leaf galls of the false dandelion H.radicata and species of the genus in several European countries and in the western USA, where they are dispersed by seeds of the weed. Leaves are often distorted, discolored and smaller, with reduced and twisted leaf stems or they may obtain a shape morphologically quite different from the normal; in many plant species galls or necrotic spots may develop.
