This treatment provides a revision of four sections of Aralia L. (Araliaceae). It is the third and last of the Aralia monographic series by the author. The first was on Aralia sect. Pentapanax (Seem.) Wen (19 species, Wen 2002); and the second was on Aralia sect. Dimorphanthus (Miq.) Miq. (29 spp., Wen 2004).
This revision treats Aralia sects. Aralia (14 spp.), Humiles (3 spp.), Nanae (1 sp.), and Sciadodendron (5 spp.). A taxonomic key to all sections of Aralia is provided. Species keys are provided for each of the three sections with multiple species. As typified by Aralia fargesii Franch., Aralia sect. Anomalae Harms is now placed in synonymy of Aralia sect. Aralia. Aralia sect. Nanae is the only monotypic section of the genus, consisting of Aralia nudicaulis L. Marchal's genus Coudenbergia is merged with Aralia sect. Sciadodendron in this study.
Detailed descriptions on the morphology and ecology, illustrations, and distribution maps are provided for each taxon of the four sections (23 species). The phylogeny of Aralia based on sequences of the internal transcribed spacer (ITS) regions of nuclear ribosomal DNA and three chloroplast markers, including the ndhF gene, the trnL-F region, and the atpB-rbcL spacer, is presented. An early biogeographic radiation of Aralia is hypothesized. Taxa of Aralia sect. Humiles do not form a clade with those of the Asian Aralia sect. Pentapanax. These two sections were once treated as constituting the genus "Pentapanax", and they are shown here to be non-monophyletic and best treated as belonging to two different sections. Aralia bahiana J. Wen is herein described as a new species from Bahia, Brazil. Aralia sect. Sciadodendron is a new nomenclatural combination with the genus Sciadodendron as its basionym. The newly lectotypified names include: Aralia cachemirica Decne., A. californica S. Watson, A. californica var. acuminata S. Watson ex Howell, A. chilapensis Sessé & Moc., A. continentalis Kitagawa, A. cordata Thunb., A. edulis Sieb. & Zucc., A. fluminensis Glaz., A. henryi Harms, A. humilis Cav., A. pilosa Franch., A. pubescens DC., A. racemosa L. var. sachalinensis Regel, Megalopanax rex Ekman ex Harms, Pentapanax ulei Harms, and Sciadodendron excelsum Griseb.