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A molecular systematic study of Scrophulariaceae sensu lato using DNA sequences of three plastid genes (rbcL, ndhF, and rps2) revealed at least five distinct monophyletic groups. Thirty-nine genera representing 24 tribes of the Scrophulariaceae s.l. (sensu lato) were analyzed along with representatives of 15 other families of Lamiales. The Scrophulariaceae s.s. (sensu stricto) include part or all of tribes Aptosimeae, Hemimerideae, Leucophylleae, Manuleae, Selagineae, and Verbasceae (= Scrophularieae) and the conventional families Buddlejaceae and Myoporaceae. Veronicaceae includes all or part of tribes Angelonieae, Antirrhineae, Cheloneae, Digitaleae, and Gratioleae and the conventional families Callitrichaceae, Globulariaceae, Hippuridaceae, and Plantaginaceae. The Orobanchaceae include tribes Buchnereae, Rhinantheae, and the conventional Orobanchaceae. All sampled members of Orobanchaceae are parasitic, except Lindenbergia, which is sister to the rest of the family. Family Calceolariaceae Olmstead is newly erected herein to recognize the phylogenetic distinctiveness of tribe Calceolarieae. The Calceolariaceae are close to the base of the Lamiales. The Stilbaceae are expanded by the inclusion of Halleria. Mimulus does not belong in any of these five groups.

Conspicuous air spaces in Leucophyllum (Scrophulariaceae; Leucophylleae) leaves have been suggested to be developmentally transformed secretory cavities. We reinvestigated air space development in Leucophyllum frutescens, using freehand sections of mature fresh leaves and paraffin sections of several leaf stages. Each of the numerous air spaces per leaf forms because greater separation occurs within a local group of spongy mesophyll cells than in the developing spongy mesophyll elsewhere. We found no anatomical evidence of transitory epithelial cells or lysis of cells in developing air spaces, thus the hypothesis that air spaces are transformed secretory cavities is not supported. However, an important finding was that all leaves had one pair of conspicuous true secretory cavities flanking the midvein at the apex, each lined by an epithelium and filled with oil. We also found conspicuous apical cavities in freehand sections of herbarium specimens of this and three other Leucophyllum species. Cavities were not seen in L. revolutum or in the related Eremogeton grandiflorus. This is the first report and description of a true internal secretory cavity in Scrophulariaceae. In the related family Myoporaceae, we found epithelium-lined cavities scattered abundantly in leaves of cleared samples of three genera.