Application of microscopy to Digitalis thapsi x Digitalis purpurea natural hybrid identification

The dried leaf of Digitalis purpurea L. (foxglove leaf) was introduced as botanical drug into the London Pharmacopoeia of 1650 and remains actually in all Occidental Pharmacopoeias (digitalis purpureae folium). During last year’s, some specimens of Digitalis L. genus collected in the Northeast region of Portugal were identified by us as natural hybrids Digitalis thapsi L. x Digitalis purpurea L.. Traditionally, hybridization in plants has been generally detected using morphological characters and the leaf is one of the most common organs used in this kind of studies. The aim of this chapter is to present a complete description of the microscopic characteristics, founded by us in the leaf of the collected samples, that allows the identification of the natural hybridization based on the application of light microscopy and scanning electron microscopy. Quantification and statistical data analysis of the major micromorphologic D. thapsi x D. purpurea leaf distinctive characters were also presented. This work emphasizes the importance and actuality of the use of microscopic techniques as a tool of identification of pharmaceutical botanical raw materials.