Dick Hamilton received 4 fruits from a cooperator in Udet Sandakin, Sabak, North Borneo [sic, see comment below]. He believes that the fruit could have been a form of rough lemon. The fruits, however, had smooth, thin tightly adherant skin, large prominent oil glands, and bitter, acrid, inedible flesh. Polyembryonic. (original CES documentation ca 1972...WP Bitters?)This accession had seedling yellows which was removed by shoot tip grafting (STG 172-1). (EM Nauer, 1986)
Fruit compared with fruit of RCRC 2316 = PI 109632, Citrus excelsa, and these two accessions appear to be identical in both fruit & foliage characteristics. May as well discard this one. (EM Nauer, 11/13/1987)
Appears to be identical to C. excelsa. (EM Nauer, 10/1988)
There are currently three accessions identified as "Citrus excelsa" (PI 109632, PI 539194, and the current accession. All three were originally received as something other than C. excelsa. C. excelsa is described in Wester (1915). The provenance of this particular accession is a little unclear since the political makeup of the area of origin has changed over the years. Best conjecture is that this is from the northeast coast of the Island of Borneo, corresponding to what is currently referred to as Sandakan, Sabah, Malaysia. It is also unclear as to when Dr. Hamilton received the fruit. Were the fruit received in Hawaii in 1972 and seeds immediately sent to Riverside, or were the seeds sent to Riverside extracted from fruit from trees grown from seeds taken from fruit sent some time previously? All personnel from that time have passed into the big repository in the sky so any additional information will not be available in this world. (RR Krueger, 09/18/2018)
Additional information and nice photographs from the UC Riverside Citrus Variety Collection.