Anatomy and distribution of foliar idioblasts in Scrophularia and Verbascum (Scrophulariaceae)

Internal secretory structures have rarely been reported from Scrophulariaceae, and foliar idioblasts only once before, in 1887. Presented here are the first unambiguous descriptions of subepidermal foliar idioblasts in the family, from Scrophularia and Verbascum, genera regarded as closely allied on other grounds. Leaf samples from 183 mostly herbarium specimens (128 species, with 55 replicates) were cleared and stained, which revealed idioblasts in 62 (69.7%) of 89 Scrophularia species and 13 (33.3%) of 39 Verbascum species. We then chose 14 representative species to examine by resin sectioning and scanning electron microscopy. Idioblasts occurred both adaxially and abaxially. Most were conspicuous, in some species penetrating to vasculature level. Idioblasts had a thin primary wall and were empty at maturity. Verbascum and Scrophularia species with and without idioblasts were scattered among the subgeneric taxa without taxonomic clustering; likewise, both types occurred in approximately proportionate numbers throughout the geographic range, except that 14 of 15 North American Scrophularia species had idioblasts. Petals of two species had abundant idioblasts. The 1887 report illustrated a huge idioblast in S. deserti and we also found the largest in either genus in this species. We also noted trichome and stomata types and report that paraveinal mesophyll and foliar endodermis with casparian strip were both absent.