bramble
brier
bristle
burr
catchweed
cleavers
goose grass
needle
nettle
pine needle
prickle
quill
spicule
spiculum
spike
spikelet
spine
sticker
thistle
thorn
yucca
Cereus
cacti
cactaceous
cactal
cactoid
acacia
bamboo
brushwood
cypress
elm
evergreen
gorse
juniper
mesquite
myrtle
pear
scrub
shrub
shrubbery
underwood
willow
actus
malpractice
practice