## 4 Discussion  
The intensity of both micro- and macro-elements in the four common leaf vegetables was comparable with those reported in similar studies [30]. The observed differences in selected specific minerals were likely due to the environmental, ontogenic and genetic factors. For instance, the application of calcium ammonium nitrate fertilizer enhanced leaf Ca content, but farmyard manure decreased Fe content in spider plant [31]. In another study involving parsley (_Petroselinum crispum_), baby greens accumulated more Ca and Mg than microgreens [32]. The superiority of micro-element content in the Swiss chard leaves relative to the common leafy vegetables which was observed in this study was consistent with findings from other similar studies [33]. However, in this study, the common leafy vegetables showed superiority in macro-element content suggesting that consumers can derive optimum benefits from combining (or including) the various types of leafy vegetables. It should be emphasized that the threshold quantities of individual nutrient elements that are necessary for human consumption per designated period are more important than the mere presence of the elements in the leaves in the vegetables. Studies have also elucidated the necessity of balancing the nutrient elements in diets and their role particularly in conferring strong bones (teeth), transmitting nerve impulses and forming integral constituents of different hormones [34]. Microelements also participate in the formation of erythrocyte cells while macro-minerals, such as Ca and Mg, have a high potential to control blood pressure and the immune system [34]. Figure 1: Principal component analysis biplot of PC1 and PC2 illustrating the variation among common traditional leafy vegetables estimated using the data set of leaf minerals, total phenolic content and antioxidant activity. Long lines indicate high correlation values, while acute angles indicate positive correlation between each pair of variables. CWP = cowpea; JTM = jute mallow; PPK = pumpkin; SCD = Swiss chard (check); SPT = spider plant; Ca = calcium; Mg = magnesium; P = phosphorus; N = nitrogen; Al = aluminum; Cu = copper; Fe = iron; Mn = manganese; Zn = zinc; FC = total flavonoid content; TPC = total phenolic content; DPPH = 2,2 diphenyl-1-picrylhydrazyl free radical scavenging activity; FRAP = ferric-reducing antioxidant power. The results also showed that no single leafy vegetable type contained all the desirable minerals, flavonoids and phenolic compounds suggesting that perhaps human intervention, particularly through genetic enhancement, can develop novel genotypes of the leafy vegetables that possess preferred combinations of the nutrients. One of the possible reasons for the observed absence of specific mineral elements or bioactive compounds in some of the leafy vegetables could be attributed to the existence of inverse relationships between them in the vegetable species. Nonetheless, such inverse relationships can be broken through plant breeding techniques such as mutation and probably the CRISPR technology [35; 36]. The results also revealed the availability of a wide range of quercetin-related compounds in all the leafy vegetables particularly in spider plant. These findings agreed with the results that were reported for a similar study [37]. The role of quercetin as an antioxidant was documented widely as a potent antioxidant flavonoid (or more specifically, a flavanol) which occurs also in onion, broccoli and citrus fruits and is protective against tissue injury caused by drug toxicities [38; 39; 40; 41]. However, it is unclear if this desirable group of nutrients can be introressed into the other leafy vegetables without diminishing the already existing beneficial nutrient elements in such vegetables. Another drawback in the study was that fresh leaf samples were processed for the analysis such that the effects (on the quality and levels of these nutrients) of homemade processing of the vegetables for long term preservation remain unclear.