International Journal of Biology; Vol. 5, No. 4; 2013 ISSN 1916-9671 E-ISSN 1916-968X Published by Canadian Center of Science and Education 36 Distribution of Leaf Flavonoid Aglycones and Glucuronides in the Genus Phaseolus and Related Genera Michelle L. Poe 1 , Andra Bates 1 & Joseph Onyilagha 1 1 Department of Biology, University of Arkansas at Pine Bluff, Pine Bluff, Arkansas, USA Correspondence: Joseph Onyilagha, Department of Biology, Mail Slot #4972, University of Arkansas at Pine Bluff, Arkansas, 71602, USA. Fax: 870-575-4602. E-mail: onyilaghaj@uapb.edu Received: July 4, 2013 Accepted: July 15, 2013 Online Published: September 9, 2013 doi:10.5539/ijb.v5n4p36 URL: http://dx.doi.org/10.5539/ijb.v5n4p36 Abstract Ninety-six species and hybrids of the genus Phaseolus and related genera, Dysolobium, Macroptilium, Strophostyles, and Vigna are surveyed for their leaf flavonoid (flavone/flavonol) aglycone and glucuronide distribution patterns. The aim is to determine whether the distribution patterns of certain flavonoid aglycones and/or glucuronides are restricted in each genus and hence, could be used to delineate the genus. The results show that flavonol aglycones (kaempferol and quercetin) are more frequent in the entire group than the flavones (luteolin and apigenin). Kaempferol is more prevalent than quercetin in the genus Macroptilium, while Strophostyles accumulates mainly quercetin. There is generally no restricted pattern for a particular type of flavonoid aglycone in Phaseolus and Vigna genera. Results also show the presence of flavonoid glucuronides in six out of 18 species of Phaseolus surveyed, but are absent in all the species of Vigna, Macroptilium, and Strophostyles. The situation in Dysolobium is inconclusive. A flavonoid band moved toward the anode during electrophoresis (a positive test for the presence of glucuronide) but glucuronic acid was not detected during subsequent analysis. In the genus Phaseolus, all the species and cultivars that accumulate flavones such as P. coccineus, P. ricciardianus and P. parviflorus accumulate flavone glucuronides, while P. vulgaris, P. tuberosus and P. zebra accumulate flavonol glucuronides. Keywords: Phaseolus, flavonoid, quercetin, kaempferol, luteolin, apigenin, glucuronide, flavone, flavonol 1. Introduction Species of the plant genus Phaseolus and its relatives are generally known as “beans”. They form important staple food crops in many countries especially in some tropical areas where protein rich beans could be substituted for meat proteins. Few species are cultivated. Two of the most important ones are P. vulgaris, which thrives in the temperate regions and P. lunatus, which prefers the tropical regions. The majority of the species is wild and is distributed in all the climatic regions. The potentials of these wild species are not yet fully realized. The precise definition of the genus has long been unclear, mainly because it is difficult to distinguish it clearly from Vigna (Evans, 1980; Onyilagha, 1993; Onyilagha & Shahidul, 2009). This confusion may have started early in Linnaean taxonomy. Linnaeus included eleven species in his genus, namely, Phaseolus vulgaris, P. coccineus, P. lunatus, P. inamoenus, P. farinosus, P. vexillaatus, P. helvulus, P. alatus, P. caracalla, P. radiatus and P. max (Linnaeus, 1753). De Candolle divides the genus Phaseolus into two sections, Euphaseolus and Strophostyles with five subgroupings in the first and two in the second. These are however heterogeneous and do not provide a satisfactory basis for classification (Candolle, 1825). Bentham gives a synopsis of the genus. He describes 85 species distributed in seven sections: Drepanospron, Euphaseolus, Leptospron, Strophostyles, Lasiospron, Microcochle and Macroptilium (Bentham, 1837). In his later work, he dropped Lasiospron and Microcochle and added Dysolobium. Since that time, Dysolobium and Macroptilium are recognized as distinct genera by Prain and Urban respectively. In his review, Piper recognized eight sections: Sigmoidotropis Piper, Ceratotropis Piper, Lasiospron, Macroptilium, Microcochle, Cochliasanthus (Trew) Piper, Leptospron and Euphaseolus (Piper, 1926). In another revision of the genus, Verdcourt recognized Macroptilium as a genus after Urban and the treatment of Sigmoidotropis, Ceratropis, Lasiospron and Cochliasanthus as sub-divisions of Vigna (Verdcourt, 1970). Phaseolus was therefore limited to only 50 species. To date, this treatment serves a practically useful classification