green, round to slightly angular stems grow to (30-)50 to 80(-100)cm in height before they start to flower. The stems are similarly entirely covered in glandular hairs; these are present in two forms: short and subsessile, or much longer, 0.4 to 0.6mm. The chromosome count is 2n=56. Leaves The lower basal leaf blades are 7.5 to 13cm (exceptionally 19cm) in length, 2.5 to 5cm in width, more or less flat but sometimes undulated along the margins, and oblong to elliptic in shape, with a sharp to somewhat sharply tipped apex. The bases of the leaves taper gradually into the petioles. The texture is soft, not leathery. The underside is rugose-reticular in texture, coloured greenish-yellow and very densely packed with glandular hairs. The leaves in the middle of the rosette are clearly decurrent. The margins are denticulate or somewhat so, rarely subentire. Flowers The pink, rarely white, flowers are arranged in an inflorescence in the form of a raceme, 15 to 35cm in length with 15 to 40 individual flowers. The inflorescence has glandular hairs along its shaft, is not stiff, and is secundiflorous, meaning the flowers follow each other in succession. The flowers have a 1 to 2cm long pedicel which is curved at the base, and shorter to equal in length to the subtending bracts. The flowers hang somewhat, and are separated by internodes of 8-15mm. The bracts are 12 to 20mm in length and 2 to 3mm broad, glandular and lanceolate in shape. Chemistry According to Dutch botanist Herman Boerhaave, writing at the turn of the 17th century, Digitalis species are highly poisonous if directly ingested. All parts are poisonous. In studies, the restriction of calcium ions resulted in cardenolide accumulation in D. thapsi. Calcium quantity affects the redox chemical reactions in the cells. Without calcium, changes in antioxidant function were observed and catalase activity was slow. In another study, lack of calcium retarded growth and promoted digoxin formation. Manganese sulfate and lithium chloride also increased the digoxin concentration, but did not affect growth. Calcium oxalate crystals have also been isolated from D. thapsi. Similar species In 1841 Pierre Edmond Boissier considered it the most similar to D. mariana, which he was then describing as a new species, having collected from the same region. In the dichotomous key in the Flora Iberica, it is keyed out to D. mariana, D. minor and D. purpurea. D. thapsi is distinguished