Originated by the geneticist and breeder, H. B. Frost, at the Citrus Research Center, Riverside, California. Fruit medium-small, elliptical to oblong, sometimes obovate; commonly with short neck or low collar at base; usually short but sometimes long apical mammilla or nipple; frequently surrounded with areolar furrow. Seed content variable but usually few to none. Color yellow at maturity. Rind medium-thick; surface finely pitted with sunken oil glands, slightly rugose, commonly with low longitudinal ridges; tightly adherent. Segments about 10; axis small and usually solid. Flesh color greenish-yellow; fine-grained, tender, juicy; flavor highly acid. Crop well distributed throughout year, but mainly in late winter, spring, and early summer. Tree medium in vigor and size, spreading and open in growth habit, virtually thornless; sparsely foliated (in comparison with Lisbon and others); strongly everbearing and produces fruit at the ends of long branches; precocious; productive. Tree lacking vigor compared with most other varieties; more sensitive to cold, insect infestation, and neglect; shorter-lived. The fruit of the Eureka variety differs in general from that of Lisbon, the principal other variety in California, in that it is more prominently ridged and has a somewhat rougher rind surface and usually a smaller and less pronounced nipple. The tree differences are much more marked. In addition to those differences, the leaves are darker in color and less sharply pointed and the margins are somewhat more crenate than the Lisbon.