Traditionally, the genus Zilla Forsk. (Brassicaceae) is conceived as composed of Z. macroptera Cosson, Z. biparmata O. E. Schulz, Z. spinosa (L.) Prantl, and Z. spinosa v. microcarpa Dur. & Sch., while some authors regard it as monotypic with two subspecies. All are spiny shrubs indigenous to desert regions from Morocco to Arabia, used locally for ailments like kidney stones. We studied Z. biparmata, Z. spinosa, and Z. spinosa v. microcarpa for glucosinolates (a characteristic Brassicaceae class). Paper chromatography showed only one identical glucosinolate in their seed-containing silique extracts. Isolation, acetylation (to crystalline K-salt acetate), enzymatic hydrolysis, and purification of hydrolysis products revealed via chemical and spectroscopic evidence the glucosinolate as 2-hydroxy-3-butenylglucosinolate, hydrolyzing to dextrorotatory 5-vinyl oxazolidine-2-thione. Rotation data (Table 1) showed consistent values for the three taxa. Previously, Z. spinosa was reported to produce levorotatory goitrin, but our data indicate the three Zilla species contain a ~9:1 mixture of (R)- and (S)-2-hydroxy-3-butenylglucosinolate. The identical glucosinolate patterns support the monotypic treatment of Zilla, consistent with recent chromosomal similarity-based classification of Z. biparmata as a Z. spinosa subspecies.