On a space the size of an average backyard grows a dozen different cacti species so thick that the ground appears covered with a "carpet of cactus."
(On a space; grows; a dozen different cacti species so thick that the ground appears covered with a "carpet of cactus) (the ground; appears; ) (the ground; covered; with a "carpet of cactus)
On a space the ground the ground
grows appears covered
a dozen different cacti species so thick that the ground appears covered with a "carpet of cactus
with a "carpet of cactus