About Croton argenteus L.
Croton argenteus L. is an annual plant that typically grows in nutrient-poor soil. It develops a large taproot, grows in an erect form, and is covered in wool-like hairs. It has alternate ash-green leaves. Tiny monecious flowers of this species grow grouped in a raceme: lower female flowers lack petals, while upper male flowers have five small yellow petals. This species is pollinated by ants. Its fruits are conspicuous, formed of three joined dark green spheres. The fruit surface is marked with white scales and warty structures. Each sphere holds three seeds, which are launched away from the parent plant by mechanical force from the twisting of the mature fruit as it opens. Croton argenteus L. is considered poisonous; consumption may cause stomach upset, vomiting, nausea, and diarrhoea. Chrozophora tinctoria produces the blue-purple colorant called turnsole, also known as katasol or folium. This colorant was used in medieval illuminated manuscripts, and as a food colorant in Dutch cheese and certain liquors. It was mostly used as a less expensive substitute for Tyrian purple, the famous dye sourced from Murex molluscs. The color comes from this plant's fruit, specifically its dry outer coat. The colorant can also be obtained from the translucent sap contained in plant cells when the plant's leaves are broken off and exposed to air. Different shades of blue and purple can be produced when juice extracts of the plant are exposed to ammonia (NH3) vapors. In late 19th century France, this ammonia exposure was achieved by applying fresh horse manure and urine to fabric soaked in the plant extract. The plant has been used historically across the Levant to dye clothing. 100 kilograms of Chrozophora tinctoria produces 50 kilograms of sap, and this amount of sap can dye 25 kilograms of fabric rolls. In 2020, an interdisciplinary research team from FCT NOVA, University of Porto and University of Aveiro identified the complex chemical structure of the medieval purple-blue dye extracted from Chrozophora tinctoria fruits. The chemical structure of this medieval dye had remained unknown until this study. The obtained extracts showed a novel blue chemical, chrozophoridine, to be the dye's main chromophore.
