Joey Hooker, smallflower galinsoga
Galinsoga parviflora Cav.
An introduced annual weed of cultivated and waste ground, locally frequent in the UK. It prefers a damp, rich soil and an open situation where there is little competition for light. Gallant soldiers was introduced from Peru into Kew Gardens in 1796.
Gallant soldiers flowers from May to October or until killed by frost. It can cross or self-fertilize and may have 3 to 4 generations in a year. The composite flower head has 3-8 ray flowers and 15-50 disc flowers. There are around 26 seeds (achenes) in a flower head. The average number of seeds per plant is 2,000 but a large plant can have up to 15,000 seeds, and a figure of 400,000 has been suggested. The seeds are shed 11 to 14 days after flowering. The disc seeds have a pappus of hairs for wind dispersal. The ray seeds have a winged structure formed by the capitulum bracts that aids wind dispersal.
In the UK, the main period of seedling emergence is from March to October and generally follows soil cultivation. In the USA, seeds can germinate soon after shedding and will germinate in spring and summer, but most germination is in the autumn. Light is needed for germination and soil burial induces dormancy in the seeds. Seeds germinate from the upper 0-20 mm of soil. Subsequent growth is encouraged by high temperatures. Gallant soldier seedlings are frost sensitive.
In the soil seedbank both ray and disc seeds remain viable for up to 2 years. The ray seeds may persist at a low level beyond this time. Viable seeds were still present after 5 years in cultivated soil. Seeds recovered during house demolitions and dated at 20 years old have been reported to germinate.
Seeds are dispersed by the wind and on clothing. The spread of gallant soldiers has been calculated at 1.6 km over 10 years.
Control is by repeated surface cultivations. It is vital to prevent seeding. Seedlings can come into flower very quickly and should be hoed off when small. With little seed dormancy, regular cultivations can eliminate gallant soldiers in 3-4 years if there is no further seeding. Putting a field down to grass for the same period has also proved effective. A thick organic mulch will prevent seedling emergence.
In its native habitat, fungal colonisation of the seeds is responsible for the decline of seed viability in the soil.
Updated November 2007.