Le Rouge et le Noir (image) BioMed Central Caption Dahlia variabilis hort. is a popular garden flower. Continuous dahlia breeding worldwide has led to the availability of a huge number of cultivars - 20,000 varieties - many of them showing red hues. However, black hues of dahlia flowers occur rarely, in comparison. Credit Dr. Heidi Halbwirth Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.