Editing Cactus (section)

===Spines===

Botanically, "[[Thorns, spines, and prickles|spines]]" are distinguished from "thorns": spines are modified leaves, and thorns are modified branches. Cacti produce spines, always from areoles as noted above. Spines are present even in those cacti with leaves, such as ''[[Pereskia]]'', ''[[Pereskiopsis]]'' and ''[[Maihuenia]]'', so they clearly evolved before complete leaflessness. Some cacti only have spines when young, possibly only when seedlings. This is particularly true of tree-living cacti, such as ''[[Rhipsalis]]'' and ''[[Schlumbergera]]'', but also of some ground-living cacti, such as ''[[Ariocarpus]]''.{{sfnp|ps=none|Anderson|2001|pp=15–37}}

The spines of cacti are often useful in identification, since they vary greatly between species in number, color, size, shape and hardness, as well as in whether all the spines produced by an areole are similar or whether they are of distinct kinds. Most spines are straight or at most slightly curved, and are described as hair-like, bristle-like, needle-like or awl-like, depending on their length and thickness. Some cacti have flattened spines (e.g. ''[[Sclerocactus papyracanthus]]''). Other cacti have hooked spines. Sometimes, one or more central spines are hooked, while outer spines are straight (e.g., ''[[Mammillaria rekoi]]'').{{sfnp|ps=none|Anderson|2001|pp=15–37}}

In addition to normal-length spines, members of the subfamily Opuntioideae have relatively short spines, called [[glochid]]s, that are barbed along their length and easily shed. These enter the skin and are difficult to remove due to being very fine and easily broken, causing long-lasting irritation.{{sfnp|ps=none|Anderson|2001|pp=15–37}}
{{center|'''Cactus spines'''}}
<gallery mode="packed" heights="160" style="font-size:95%; line-height:120%">
Ferocactus1001.jpg|Varied spines of a ''[[Ferocactus]]''
Hakendornen IMGP7026 WP.jpg|Hooked central spine (cf. ''[[Mammillaria rekoi]]'')
Toumeya papyracantha fh 087 3 AZ BB.jpg|Unusual flattened spines of ''[[Sclerocactus papyracanthus]]''
Opuntia microdasys 01 ies cropped.jpg|Glochids of ''[[Opuntia microdasys]]''
</gallery>