CYANOGENESIS IN ACACIA FARNESIANA

Abstract

Among the mimosoid legumes, few species exhibit the systematic complexity of Acacia farnesiana (L.) Willd. This widespread assemblage of species or microspecies is probably native to the Americas [1-3] and has subsequently been introduced into other tropical and subtropical regions throughout the world. In the Americas, Acaciafarnesiana (sensu lato) is found from the southern U.S. to Argentina. Plants are often irregular in form but are sometimes spreading and flat-topped [4, 5]. It is often distinguished only with difficulty from species such as A. tortuosa and A. macracantha [1,6] and in Africa shows affinities toward A. sieberiana [1]. Several taxa have been segregated from the Acaciafarnesiana species complex. A. smallii is widely distributed in the southern U.S. and northern Mexico [7]. A. pinetorum, another north American segregate, occurs in S. Florida [7]. Acacia caven is an extra tropical South American taxon with close affinities to A. farnesiana. Acacia farnesiana (based on Mexican)Ilaterial which was not A. smallii) is a tetraploid (2n = 52). A. caven is a diploid (2n = 26). Apparently neither A. smallii or A. pinetorum have been examined cytologically [7]. Vassal [3] subdivided the subgenus Acacia section Acacia into two subsections Pluriseriae and Uniseriae based largely on fruit morphology. Acaciafarnesiana and its relatives are members of the Pluriserieae. Only one cyanogenic member of the Pluriserieae has previously been investigated. A. giraffae, a common African savanna species, is known to contain proacacipetalin as the major cyanogen [8]. Acacia farnesiana has been reported to be both cyanogenic [9, 10] and acyanogenic [11]. Recent investigations have suggested that the cyanogens are linamarin and lotaustralin [8, 9, 12].