E x t e n s i on  G a r d e n e r - B o t a n y  E x e r c i s e s


This exercise focuses on the common structures plants use to defend themselves: prickles (modified hairs), spines (modified leaves), and thorns (modified stems). First, study the images below to review the relevant terms. Then, carefully study the unsorted images at left and drop each thumbnail into an appropriately labeled box on the right. Clicking on a thumbnail will expand the image. Click submit to check yourself. To reset, click clear or just refresh your browser.

Note that it's the position of the structure that provides a clue to its derivation. Thus, a spine is borne in the position of a leaf or stipule (i.e., below an axillary bud). In contrast, a thorn, being a modification of a stem, is borne immediately above the leaf (or where a leaf would be). Prickles, being modified hairs, are borne throughout the stem, with no particular relation to the nodes.

Examples of plants with prickles include most blackberries and raspberries (Rubus spp.), Devil's-walking-stick (Aralia spinosa), Hercules-club (Zanthoxylum clava-herculis), roses (Rosa spp.), and greenbriars (Smilax spp.). Plants with spines include some barberries (Berberis spp.) and black-locust (Robinia pseudoacacia). Plants with thorns include many hawthorns (Crataegus spp.), firethorns (Pyracantha spp.), and honey-locust (Gleditsia triacanthos).

Illustrations depicting the differences between prickles, spines, and thorns

   © 2018–present: Dr. Alexander Krings, unless otherwise noted. Last updated Jul 2018.