Any of about 200 varieties of club moss. The commonest is the staghorn moss Lycopodium clavatum from which a resinous, reticulate-shaped pollen is obtained. This is commercially available and is characterized by a relatively spherical, uniformly sized particle (surface average diameter 29 mm, typically with 80 wt% contained within 25-35 mm) suitable for calibration purposes. When tested by non-inductive sparks in various dust ignition energy apparatus under the auspices of ASTM, its minimum ignition energy has been found to be about 20 mJ. This is believed to correspond to, or exceed, the maximum effective energy of bulking brush discharges.
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