saguaro: extremely large treelike cactus of desert regions of southwestern United States having a thick columnar sparsely branched trunk bearing white flowers and edible red pulpy fruit
cactus: any succulent plant of the family Cactaceae native chiefly to arid regions of the New World and usually having spines
pollen tube: (botany) a slender tubular outgrowth from a pollen grain when deposited on the stigma for a flower; it penetrates the style and conveys the male gametes to the ovule