Chemotaxonomic Significance and Environmental Implications of the Phytochemical Constituents of four Mussaenda L. (Rubiaceae) taxa in Nigeria

Abstract

This work investigated the phytoconstituents of some Mussaenda taxa (Rubiaceae) collected from Nsukka (Derived Savanna) and Uyo (Tropical Rainforest) ecological zones of Nigeria to establish their contribution as possible taxonomic and environmental monitoring markers. Fresh leaf samples used in this study were collected from plants of the same age, air-dried, and made into powder for further use. Histochemical and phytochemical tests were carried out by following the standard procedures. Results of the comparative phytochemical screening revealed the presence of flavonoids, alkaloids, glycosides, phenols, hydrogen cyanide, reducing sugars, soluble carbohydrates, saponins, steroids, terpenoids, and tannins in varying proportions. Results of the phytochemical constitute analysis revealed the presence of the cystoliths from the M. elegans (MEL) and M. erythrophylla (MER) which were absent in Mussaenda “ Doña Aurora” (MDA) and Mussaenda “Doña Luz”(MDL). Further, the presence of the Raphides was unique to MEL while Gum and mucilage were reported only in MDA. Quantitatively, MEL had the highest value of terpenoids (650.88 mg/100g) while MDA had the highest values of phenols (899.27 mg/100g), alkaloids (311.01 mg/100g), reducing sugars (967.35 mg/100g), steroids (2.89 mg/100g), soluble carbohydrates (27.68 mg/100g) and tannins (393.16 mg/100g), and MDL was richest in glucosides (339.64 mg/100g), flavonoids (69.34 mg/100g) and hydrogen cyanides (1.34 mg/100g). The cluster analysis based on obtained phytochemical data revealed three (3) distinct clusters with MEL in cluster 1; MDA and MDL in cluster 2 while cluster 3 had MER.  The evolutionary closeness of the two infraspecific and exotic species (MDA and MDL) were confirmed and their taxonomic relationship with the indigenous infrageneric taxa (MEL and MER) was established. The results also highlight the opportunity of employing plant metabolomics in ecological studies and environmental monitoring.