Crossing and Morphological Relationships among Species Closely Related to Arrowleaf Clover¹

Isolation barriers were examined by making all possible crosses including reciprocals among arrowleaf clover ( Trifolium vesiculosum Savi), T. mutabile Portenschl. and T. leiocalycinum Boiss. & Spruner. No evidence of sterility was indicated by cross seed set. All F 1 cross seed germinated readily but yellow seedlings were produced by crosses of T. mutabile and T. leiocalycinum with T. vesiculosum . F 1 plants from reciprocal crosses of these species were normal green. The yellow condition disappeared as plants matured. Most F 1 plants from crosses between accessions produced less stainable pollen than plants from crosses within accessions. All species had 16 somatic chromosomes and chromosome associations at metaphase I of meiosis were similar for all parents and F 1 progenies. We concluded that T. mutabile and T. leiocalycinum are quite closely related and are slightly differentiated from T. vesiculosum . Therefore, the three taxa must be isolated under field conditions to prevent crossing.