Ploidy was determined for 15 plants labeled as Juniperus squamata at the Windsor Gardens, UK and revealed 12 were tetraploids (2n=4x=44) and 3 were diploids (2n=2x=22). nrDNA (ITS) and cp DNA sequencing the tetraploids found: 4 J. squamata (4x); 4 J. tibetica (4x) x J. squamata (4x); 2 J. sabina var. balkanensis (4x) x J. squamata (4x); and one J. chinensis var. sargentii (4x) x J. squamata (4x). Sequencing the 3 diploids revealed: 2 J. pingii (2x) x J. pingii (2x); and 1 J. pingii (2x)? x J. komarovii(2x)? Ploidy analyses of 18 additional cultivars, putatively from Juniperus davurica, J. recurva, J. rushforthiana, J. sabina, and J. virginiana revealed 6 diploids, 5 triploids and 7 tetraploids. Cultivar 'Musgrave' (4x), by DNA, was identical to J. xpfitzeriana 'Wilhelm Pfitzer' (4x). The DNA of the 5 triploids were all nearly identical to J. xpfitzeriana 'Wilhelm Pfitzer' (4x). 'Tamariscifolia' and 'Variegata' both had J. sabina var. sabina as their maternal parent, but the first had J. sabina var. balkanensis as the male parent and the second had J. sabina var. sabina as the male parent. Thus, 'Tamariscifolia' is the first discovery of a J. sabina var. balkanensis x J. s. var. sabina hybrid in cultivation. None of the 3 'davurica' cultivars proved to be J. davurica, but rather J. chinensis var. procumbens x J. chinensis var. sargentii. Cultivars J. indica and recurva 'densa' were shown to be J. indica var. caespitosa. recurva ' Embley Park' appears to be J. coxii x J. squamata var. wilsonii. J. wallichiana (=J. indica) 15460 was found to be J. rushforthiana, whereas J. wallichiana (15487) was discovered to be J. indica x J. rushforthiana. Cultivar virginiana 'cannaertii' was shown to be J. virginiana. Botanic gardens provide a great opportunity for species to hybridize with other species that are not in contact in nature. The species care and suitable habitat provided in a garden setting, as well as vegetative propagation methods have allowed the preservation of those rare hybrids). Identification of juniper hybrids and variants is quite imprecise. DNA barcoding of cultivated plants in botanic gardens would greatly facilitate the recognition, study and utilization of rare hybrids and somatic mutations.
Adams, R. P., S. T. Johnson, J. Anderson, K. Rushforth, N. Valentin, A. E. Schwarzbach and S. Sijak-Yakovlev. 2020. Nuclear and chloroplast DNAs reveal diverse origins and mis-identifications of Juniperus cultivars from Windsor Gardens, UK, Part 3 of 3. Phytologia 102(3): 150-161.