Thornton Tangelo

USDA Circular 181 places Thornton among Walter T. Swingle’s 1899 Florida hybrid series. The authors say the original records were lost, grapefruit was the known seed parent and the pollen parent was not definitely known; tangerine-like sister hybrids led them to infer tangelo character.^⁠[5]

The 1931 Circular describes fully ripe Thornton fruit as sweet, juicy and free-peeling, with 10–25 seeds per fruit and acidity somewhat lacking when fully ripe. UCR’s dated April 1987 accession note instead describes a medium-sized, rough orange fruit as tart and moderately seeded.^⁠[5]⁠[1]

The Circular gives a December–March season and reports excellent quality from intensely hot, irrigated Indio in the Coachella Valley. UCR lists Riverside ripening from January to March; Robinson’s 1934 Florida account describes a December–March shipping season for Thornton and says the fruit did not ship well.^{⁠[5]⁠[1]⁠[2]}

In a nonirrigated Brazilian trial of Marsh grapefruit on ten rootstocks, Thornton induced the highest acidity and lowest juice content in Marsh fruit. The trial’s fruit-quality results describe the Marsh scion/rootstock treatment, not Thornton tangelo fruit.^⁠[4]