Zanthoxylum williamsii Standl., Ceiba 1: 41. 1950.
Arbustos, or treelets 2–4 m de alto, troncos armados con acúleos, some branchlets with numerous straight spines, short-shoots numerous usually globose and cushion-like 0.5-1 cm diameter (rarely elongate to ca 1 cm long)and ferruginous-lanate, without zig-zag growth form; apical bud ca 3 mm diameter, ferruginous-lanate; branchlets 2-4 mm wide, with sparse tufts of ferruginous hairs, glabrescent. Hojas mainly from short-shoots (and less frequently some alternate and evenly distributed), imparipinnadas, 3-8 cm de largo, rachis terete, 0.5-1 mm wide; folíolos 3-7, lateral folíolos oblanaceolate, 0.7-3.2 cm de largo y 0.4-2.1 cm de ancho, ápice rounded to obtuse and emarginate, base rounded to acute, margen crenate or crenulado, sometimes slightly revolute at base, ferruginous-lanate when young, glabrescent, chartaceous, 4-5 pairs of secondary veins, sésiles. Inflorescences from short-shoots, unbranched and head-like or 2 or 3 times branched, the branches ending in head-like or corymbose clusters, peduncles 0.5-1 cm long, terete, ferruginous-lanate and white spreading haris, heads 0.5-0.8 cm in diameter, pedicels 0-0.5 mm long and 0.1 mm wide, lanate; perianth-parts not differentiated, 8 or 10, oblong, ca 1 mm long, ferruginous-lanate on margins, deciduous or retained in part; estambres 4 or 5; carpels 1 (2). Folículo 1 or 1 and 1 aborted, 7-9 mm de largo, sparsely pubescent to glabrate, without stipe; seed ca 7 mm de largo.
Poco frecuente, bosques húmedos, zona norcentral; 750–1300 m; fr sep–dic; Moreno 22349, Stevens 15698; Honduras y Nicaragua. Reynel (1995) places Zanthoxylum williamsii in synonymy of Zanthoxylum ciliatum Engl., a species described from Venezuela, which differs in fruit and seeds ca 1/2 as long and the lateral branches longer than in Z. williamsii. Reynel also cites as synonyms of Z. ciliatum two taxa, Fagara pilosissima Engl. (Veracruz, Mexico) and Zanthoxylum purpusii Brandegee (Puebla, Mexico), which seem much closer to our species. The relationships of these three names/taxa remain unresolved. Reynel also cites Z. tenuipes Standl. (Chiapas, Mexico)as a synonym of Z. ciliatum; this appears more likely to be a synonym of Z. mollissimum.