Box 3. Categorical estimates of spinescence

(1) No spines.

(2) Low or very local density of soft spines<5mm long; plant may sting or prickle when hit carelessly, but not impart strong pain.

(3) High density of soft spines, intermediate density of spines of intermediate hardness, or low density of hard, sharp spines>5mm long; plant           causes actual pain when hit carelessly.

(4) Intermediate or high density of hard, sharp spines>5mm long; plant causes strong pain when hit carelessly.

(5) Intermediate or high density of hard, sharp spines>20mm long; plant may cause significant wounds when hit carelessly.

(6) Intermediate or high density of hard, sharp spines>100mm long; plant is dangerous to careless large mammals, including humans.