Identification of Justicia secunda Vahl by IR spectroscopy

Justicia secunda Vahl belongs to the family of Acanthaceae and is a barely examined species. In Latin America and Africa, the leaves of J. secunda are applied in ethnomedicine against indications related to anaemia [1], hypertension [2], and diabetes [3]. J. secunda grows wildly as well as in cultivation without any difficulties. Our extensive macroscopic and anatomical investigations [4] revealed that other closely related species are easily mistaken for J. secunda. The aim of this study was to establish Infrared (IR) spectroscopy as fast and reliable alternative for the proper identification of J. secunda. Cut and dried leaves of correctly identified J. secunda populations from Ecuador and French Guiana were applied to generate a database with 40 samples. In addition, correctly and incorrectly identified samples from the following materials were compared to the database: a greenhouse-cultivated population with origin in Venezuela and 20 voucher specimens from a wide region around the world. All IR spectroscopy measurements were conducted with dried leaf material that remained completely untreated prior to analysis. The data evaluation via principal component analysis lead to the result that IR spectroscopy is able to correctly identify J. secunda leaves as well as to distinguish the plant from other even closely related species. As a conclusion, we can present IR spectroscopy as fast and reliable alternative for plant identification.