Spatial Variation of Prickle Abundance on Leaves of the Devil's Walking Stick (Aralia spinosa; Araliaceae) during the Trunk-Building Phase

BRIAND, C.H. AND C.L. SOROS (Department of Biological Sciences, Henson School of Science and Technology, Salisbury University, Salisbury MD 21801, USA and Department of Botany, University of Toronto, Toronto, ON, Canada M5S 3B2). Spatial variation of prickle abundance on leaves of the devil's walking stick (Aralia spinosa; Araliaceae) during the trunk-building phase. J. Torrey Bot. Soc. 128: 219-225. 2001 -The bi-tripinnately compound leaves of Aralia spinosa are covered on both their axes and leaflet surfaces with numerous prickles. There was a positive correlation between prickle density on the adaxial and abaxial leaf surfaces, with prickle density highest on the adaxial surface. Although prickle density declined with both ramet height and leaf position along the length of the stem, only about 8% of this variation could be explained by either of these variables. Leaf prickle density varied considerably among ramets within a site, but varied little among sites. Prickles were always associated with veins and the prickles represent outgrowths of the epidermis and underlying parenchyma cells. No vascular connection exists, however, between veins and adjacent prickles. The epidermis of prickles was found to be highly lignified and covered with a thick cuticle. Leaf prickles may (1) act to deter insects from landing and/or crawling on the leaflets, especially the adaxial surface; (2) deter large herbivores from feeding; (3) protect fruit from frugivores other than seed dispersers; or (4) protect stems from physical damage by larger animals.