Thorns - Heavy, thick sharp-pointed branches as opposed to spines which are defined here as relatively small or thin modified leaves.
Curved spines - Usually short spines Less than 1/2 inch long.
Hooked spines - Spines sharply curved at the ends like a fishhook. These spines can be small and thin or large and heavy.
Short straight spines without sheaths - Spines about a half inch long or less. Not sheathed. Test by pulling on the spine with two fingers.
Short straight spines with sheaths - Spines about a half inch long or less. Test by pulling on the spine with two fingers.
Long straight spines without sheaths - Spines about an inch or more long. Not sheathed. Test by pulling on the spine with two fingers.
Long straight spines with sheaths - Spines about an inch or more long with sheaths. By grasping the spine with two fingers and pulling, the sheath will become evident as it comes off.
Spine tipped leaves - Heavy, stiff elongated leaves with extremely sharp spines at the ends.
Spiny leaves - Leaves of various shapes with spines around the margins.
Spiny involucres - Plants in the aster (composite, sunflower, daisy, etc.) family with spines at the tips of the bracts at the base of the flower heads.
Spiny around flowers - Spines at the base of flowers not in the aster family.
Spiny fruits - Plants bearing fruits with spines (often hooked) on the fruits.
Glochids only - Cacti without normal spines but bearing extremely sharp, tiny, hairlike projections where the spine would be (areoles). These are called glochids and are extremely irritating to the skin.
Very short spines - Spines thicker than glochids (sharp, hairlike projections on certain cacti) but only about 1/4 to 3/8 inch long.