Crossing and Morphological Relationships among <i>Trifolium</i> Species Closely Related to Strawberry and Persian Clover

The genus Trifolium consists of eight sections including Vesicaria, which might be termed the bladder clovers. Two centers of diversity within the section are the north Mediterranean region and the eastern part of Irano‐Taranian region. The two species of agricultural importance in the USA are the perennial strawberry clover ( T. fragiferum L.) and the annual persian clover ( T. resupinatum L.). The overall objectives of these investigations were to determine the evolutionary relationships among Vesicaria taxa, and to provide data for future possible interspecific hybridizations leading to improvement of the cultivated species of the USA as well as to authenticate the validity of nomenclature for taxa existing in the USDA world seed collection maintained at the University of Kentucky. To accomplish these objectives, breeding system, crossing and morphological relationships among eight taxa were examined in greenhouse investigations. Close similarities were indicated for two annual allogamous species, T. resupinatim and T. clusii . These species were considerably different from two other annual species, T. tomentosum L., and T. bullatum Boiss, both of which are autogamous. Among the perennial group, T. fragiferum appeared quite closely related to T. neglectum C.A.M. The other two perennial species, T. physodes Stev. ex M.B. and T. tumens Stev. ex M.B. are genetically isolated and morphologically different from each other and other species of the section. Shriveled seeds were produced from crosses of some species indicating the possiblity of producing interspecific hybrids via embryo rescue and tissue culture. Gene transfer among the species indicated as closely related by crossing investigations should be rather easy.