PRICKLE DISTRIBUTION IN ARALIA SPINOSA (ARALIACEAE)

The density of Aralia spinosa prickles varied with the age and architectural position of annual increments. Prickles were most common on young (1-4 years old, 2-3 m tall), unbranched stems. Prickles were less common on branches and were absent on inflorescences. Ramets that grew as sprouts after injury had more and longer prickles than ramets that had not arisen in this way. Leaf prickles were also more common on the leaves of trunk annual increments than on the leaves of branch annual increments. As with stem prickles, leaf prickles were more common on the leaves of stems that had sprouted after cutting than on the leaves of ramets that had not been previously cut. As bark developed, stem prickles were lost at a rate of about 10% per year. While dense prickles characterized young individuals, older individuals (> 15 years old) had very few prickles. ARALIA SPINOSA L. is a small tree of disturbed patches in the deciduous forests of eastern North America. Among Aralia's distinctive traits are large, bi-tripinnately compound, leaves, large terminal inflorescences, and abundant prickles on stems and leaves. While engaged in a study of the shoot architecture of Aralia spinosa (White, 1984), I noted that young, unbranched individuals were often more densely prickly than older Aralia individuals in the same population. I therefore posed the question: is the change in armature related to architectural development in Aralia? The shoot architecture of Aralia is distinctive (White, 1984). During the first three to five years of growth (the "trunk-building" phase), the ramet grows upward at 75 cm per year and is sterile and unbranched. During this phase, the spread of leaf area is accomplished entirely by means of the large, compound leaves. On average the ramets flower in their third or fourth year. The year after flowering, branches develop and the ramet slows greatly in annual extension growth. This study characterizes the distribution of Aralia prickles in space (i.e., their distribution relative to stem height and architecture) and time (i.e., their production, persistence, and relation to ramet development and bark formation).