Phytogeographical, morphological, and molecular evidence for the widespread but sporadic occurrence of sterile hybrids between Leucaena leucocephala subsp. glabrata and L. esculenta subsp.esculenta in South-Central Mexico is presented. Most morphological and DNA characters studied in the putative hybrids showed states intermediate between the proposed parental taxa. The occurrence of non-additive nuclear ribosomal DNA phenotypes is discussed and the need to use a suite of nuclear taxon-specific markers to determine hybridity is emphasized. The origin of the hybrid is discussed in relation to the disruption of the distributions of both parental taxa through use by man as minor food plants, providing another example of the important influence of human interference on the evolution of Leucaena. The successful use of dried leaf material as a source of DNA is highlighted as an efficient way to identify sterile hybrids at the molecular level.
Hughes, C.E.; Harris, S.A. The identification and characterisation of a naturally occurring hybrid in Leucaena (Leguminosae: Mimosoideae). Plant Systematics and Evolution (1994) 192: 177-197.