Comparative Morphology, Anatomy and Phytochemistry of Four (Two Specific And Two Infraspecific) Taxa of Mussaenda L. (Rubiaceae) Across Nsukka and Uyo Metropolises in Nigeria

Abstract

This work was carried out to study the comparative morphology, anatomy and phytochemistry of four taxa of Mussaenda L. (Rubiaceae). Each of the taxa was collected from its natural region of provenance in two different ecological (Derived Savanna and Tropical Rainforest) zones of Nigeria. Morphological observations were made in the field while anatomical studies were carried out on the leaves and the wood. Results from the comparative morphology showed that all the taxa possess common characteristic features of Rubiaceae – opposite leaves, fused corolla, fused calyx, inferior ovaries and the presence of interpetiolar stipules but differ in their habits, flower colour: corolla orange in M. elegans, creamy in M. erythrophylla, and yellow in M. phillipica var. aurorae and M. ‘Dona Aurora’; sepals absent in M. elegans but red in M. erythrophylla, greenish white in M. phillipica var. aurorae and pink in M. ‘Dona Aurora’, lamina shape (elliptic in all except M. ‘Dona Aurora’ which is ovate), lamina size, petiole length, number of lateral veins and presence and number of petaloid sepals. In all the taxa, leaves were hypostomatic and had paracytic type of stomata; irregularly shaped epidermal cells with wavy cell walls. Similarly, simple, multicellular and uniseriate non-glandular trichomes were a common feature in all taxa. However, stomatal density, index and sizes, and trichomes density, index and sizes differed significantly at P ≤ 0.05. The wood was diffuse porous in all taxa except in M. ‘Dona Aurora’ which was semi-diffuse porous. However, absent to scanty paratracheal axial parenchyma, septate fibres, pitted, solitary or in radial multiples of 2 - 4 or more pitted vessels, storied heterocellular rays and simple perforation plates (Wood Type II) were common features. Quantitative study showed considerable variations among the four taxa (M. elegans, M. erythrophylla, M. phillipica var. aurorae and M. ‘Dona Aurora’): fibre lengths were 0.80 ± 0.02 µm, 0.70 ± 0.05 µm, 0.65 ± 0.03 µm and 0.64 ± 0.04 µm respectively; fibre diameters were 0.019 ± 0.00 µm, 0.015 ± 0.00 µm, 0.020 ± 0.00 µm and 0.014 ± 0.00 µm respectively; fibre lumen diameters were 0.010 ± 0.00 µm, 0.009 ± 0.00 µm, 0.014 ± 0.00 µm and 0.091 ± 0.00 µm respectively; fibre cell wall diameters were 0.005 ± 0.00 µm, 0.005 ± 0.00 µm, 0.006 ± 0.00 µm and 0.004 ± 0.00 µm respectively; vessel lengths were 0.025 ± 0.00 µm, 0.033 ± 0.00 µm, 0.032 ± 0.00 µm and 0.044 ± 0.00 µm respectively; vessel pore diameters were 0.001 ± 0.00 µm, 0.001 ± 0.00 µm, 0.006 ± 0.00 µm and 0.001 ± 0.00 µm; vessel densities were 24.69 ± 1.40 mm-2, 60.33 ± 3.15 mm-2, 11.45 ± 0.90 mm-2 and 40.31 ± 1.78 mm-2 respectively. Phytochemical screening showed the presence of all the tested phytochemicals (alkaloids, flavonoids, glycosides, hydrogen cyanide, phenols, reducing sugars, saponins, soluble carbohydrates, steroids, tannins and terpenoids) in different proportions, with M. phillipica var. aurorae and M. ‘Dona Aurora’ having the highest distribution of phytoconstituents in mg/100 g. In summary, the highest contents of phytochemicals were seen in M. elegans (terpenoids: 650.88 ± 0.36), M. “Doña Aurora” (alkaloids: 311.01 ± 0.37, phenols: 899.27 ± 0.04, reducing sugars: 967.35 ± 0.21, soluble carbohydrates: 27.68 ± 0.01, steroids: 2.89 ± 0.03 and tannins: 393.16 ± 0.45) and M. “Doña Luz” (flavonoids: 69.34 ± 0.15, glucosides: 339.64 ± 0.22 and hydrogen cyanides: 1.34 ± 0.18). From this study, it was observed that ecological factors affected the morphology and anatomy, as well as the phytochemical constituents which could be attributed to changing environmental conditions. The results thus, could be used as important diagnostic tools in delimitation of the four taxa of Mussaenda L. and for environmental monitoring.