The Areole - Unique to Cacti ... 2/3

Spines

Spines may be just the reason some people grow cacti!

They come in all sorts of flavours: Straight, Hair-like, Hooked, Curved, Twisted, Bristles, Pectinate, Comb-like, feather like, plumose, Thick, Thin, Broad, Appressed, Glocids, Sheathed, Narrow, Hard, Soft, White, Black, Coloured, Ridged, Smooth. Even absent altogether !!

Pelec

Even on the same areole the spines may be different e.g.. a strong central spine surrounded by radial spines, or multi-coloured like a rainbow (Echinocereus is an example).

spines The spine is probably a reduction of the leaf stalk through evolution (Spines are modified bud scales, leaves and spines consist of similar tissues and spines are penetrated by vessels and have traces of chlorophyll) to adapt to the drier conditions and/or give armature to defend off animals.
Still other spines are barbed and so attach to skin/fur/clothing and enable the plant or an offset to be carried to a new location and re-root and grow. Also spiny fruit means the fruit can be transported away from the mother plant for germination in a new area.
Spines and tuffs of hairs also protect the delicate meristem/growing bud below.
Spines can collect condesation of water in the desert air at night, or in fog patches, channelling it down the stem to the roots.
White dense spines and hair/wool covering a cactus protect it from the high intensity (UV) light.

Opuntias have special spines called "Glochids" - and they are not to be messed with - they are small and barbed. A helpful hint to get them out of the skin, if you are unfortunate enough to brush against an opuntia, is to place sticky tape/sellotape on your skin and then pull it off, hopefully taking the glochids with them (a depilatory !?).