Bristle-grasses
What are they?
This distinctive group of grasses is largely found in the world's tropical and warm temperate zones, but a number of species have proven popular as food for captive and semi-captive birds, from cagebirds to pheasants and poultry. Because of this, they are widely introduced around the world as crop plants or as cover strips. Bristle-grasses have a very distinctive structure to their flowers, with the small, globular spikelets being hidden amongst an often dense array of bristles (hence their name!).
Where are they found?
These plants are most often found growing where planted as cover strips around the margins of fields (typically mixed in with other alien grasses and/or as an understory to Maize). They also often turn up in gardens as spillage from birdfood and can spread from such places to be temporarily established as urban weeds.
Identification
Click here for help with some of the terminology used on the grass pages. Bristle-grasses are easily told from most other grasses by their narrowly cylindrical heads made up of a large number of small, globular spikelets, surround by a series of stiff bristles. Each spikelet typically consists of one to two florets, with the lower floret (where present) barren or only with male parts and the upper floret with both male and female parts. Identification of the various species requires noting the size and shape of the flowerhead and the number and arrangement of the bristles. Note also the details of any barbs on the bristles.
Yellow Bristle-grass Setaria pumila
An introduced annual, occasionally planted for pheasant cover on field margins or occurring from bird feeder spillage. Flowers July to October. Plants 6-75cm in height, forming loosely tufted clumps or solitary stems. Leaf blades 6-10mm wide, hairless or hairy towards the base. Leaf sheaths rounded, hairy on the margins. Ligule a fringe of silky hairs. Flower spike upright, 1-15cm long. Spikelets 3-3.3mm, globular and densely packed, with 1-2 florets; each spikelet accompanied by 5-10, yellow bristles that bear forward-pointing barbs.
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Green Bristle-grass Setaria viridis
An introduced annual, occasionally planted for pheasant cover on field margins or occurring from bird feeder spillage. Flowers August to October. Plants 10-60cm in height, forming loosely tufted clumps or solitary stems. Leaf blades 4-10mm wide, hairless. Leaf sheaths rounded, hairy on the margins. Ligule a fringe of silky hairs. Flower spike very variable, typically upright but may arch over in larger, mature specimens, 1-10cm long. Spikelets 2-2.5mm, globular and densely packed, with two florets; each spikelet accompanied by 1-3 bristles that bear tiny, forward-pointing barbs.
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Rough Bristle-grass Setaria verticillata
An introduced annual, mostly occurring in the past as a crop impurity but more recently from bird feeder spillage. Flowers July to September. Plants to 50cm in height. Leaf blades 3-8mm wide, sparsely hairy. Leaf sheaths slightly compressed, hairy on the margins. Ligule a dense fringe of short hairs. Flower spike upright or slightly nodding, up to 10cm long, often rather open towards the base. Spikelets 2-2.3mm, elliptical, flat on one side with two florets; each spikelet accompanied by 1-3 bristles that bear tiny, backward-pointing barbs. The barbs are distinctive on this species and often snag on nearby vegetation, or even entrap insects. This often results in clusters of flower spikes hooking together and becoming entangled, which doesn't seem to happen with the other species.
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on bristles |
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Foxtail Bristle-grass Setaria italica
(Foxtail Millet, Panorama Millet) An introduced annual, occasionally planted for pheasant cover on field margins or occurring from bird feeder or cagebird spillage. Flowers July to August. Plants up to 100cm in height. Leaf blades 6-20mm wide, hairless but rough on the upper surface. Leaf sheaths loose, smooth but hairy on the margins. Ligule a thick fringe of hairs. Flower spike upright and narrow at first but arching over strongly as the seeds develop, up to 30cm long. Spikelets 2.5mm, globular and densely packed, with two florets; each spikelet accompanied by 2-5 bristles that bear forward-pointing barbs. A much larger species than the other bristle-grasses and probably originating in cultivation from a form of Setaria viridis. Well-known for producing the 'millet-sprays' fed to cagebirds.
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Nodding Bristle-grass Setaria faberi
An introduced annual, seldom recorded in the UK and with just a small handful of old records from Cambridgeshire and West Suffolk. Flowers August to October. Plants 40-80cm in height, forming loosely tufted clumps or solitary stems. Leaf blades 8-20mm wide, hairy. Leaf sheaths rounded, hairy on the margins. Ligule a fringe of hairs. Flower spike typically arching stongly over in mature specimens, 5-10cm long. Spikelets 2.7-3mm, globular and densely packed, with two florets; each spikelet accompanied by 1-6 (usually 3) bristles that bear tiny, forward-pointing barbs.
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on bristles |
Knotroot Bristle-grass Setaria parviflora
Introduced from North America, probably as a grain impurity and in bird seed. Recorded in the past from Ipswich and Cambridge. Flowers August to October. Plants 20-100cm in height, forming spreading patches by way of a nodular root system. Leaf blades 3-8mm wide, typically held erect. Ligule a fringe of hairs. Flower spike upright 1-10cm long, on slender, sometimes arching, stems. Spikelets 2-2.5mm, globular and densely packed, with two florets; each spikelet accompanied by 4-12 bristles that bear tiny, forward-pointing barbs. Differs from all other bristle-grasses in being perennial and spreading by way of nobbly, rhizomatous roots, though this may not be apparent in young plants.
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