'Rose Lantern': a New Cultivar of Koelreuteria Paniculata, the Golden-Rain Tree
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’Rose Lantern’: A New Cultivar of Koelreuteria paniculata, the Golden-Rain Tree Frank S. Santamour, jr., and Stephen A. Spongberg Modern techniques of molecular biology can be a valuable tool in unravelling the confusion that occasionally surrounds important horticultural plants. The discovery of a new cultivar sometimes the history of Koelreuteria paniculata ’Septem- involves a degree of serendipity, particularly ber’ as well as the "discovery" of ’Rose Lantern’, when one has known the plant in question for the cultivar name we have chosen for the two many years and has assumed that it was cor- Arnold Arboretum trees. rectly identified when it was received. These Between August 25th and 27th of 1958, the circumstances certainly apply to the situation late Joseph C. McDaniel of the University of recounted here, and we hope that this article Illinois’ Department of Horticulture, attended a will help to resolve any confusion that may meeting of the American Institute of Biological have arisen surrounding two very promment Sciences on the campus of Indiana University trees growing in the collections of the Arnold in Bloomington. While there, he was surprised Arboretum. to see two mature trees of Koelreuteria m On October 7, 1994, the senior author (FSS, full flower so late m the growing season: most Jr.) was visiting the Arnold Arboretum, and the golden-rain trees flower in late June and junior author (SAS) was pleased to be able to early July, and the capsules on their large accompany his colleague from the United States infructescences have already developed by National Arboretum through the Arboretum’s mid-August. McDaniel continued to observe collections and to help locate plants of particu- these trees for several years and found that they lar interest. Two accessions of Koelreuteria consistently flowered from late August into paniculata Laxmann were pointed out, along early September. with plants of the same species of a somewhat Seeds from these trees were subsequently smaller stature that had been grown from seed distributed to several attendees at the 1960 collected in Korea in 1977 by Spongberg and meetmg of the International Plant Propagators Richard E. Weaver, Jr. (Spongberg, 1978). While Society, Eastern Region. In addition, on Decem- the plants of Korean provenance were of interest ber 5, 1960, seeds of the more floriferous of the because of their habit, the senior author was two trees were supplied to Sylvester G. March at truly astonished by the two older accessions the National Arboretum, where the seed lot was (AA 577-66 and 771-68), which were labeled as given the accession number NA 16548. Several the cultivar ’September’. Knowing this cultivar seedlings of this accession were planted in a only from the Arboretum accessions, the junior nursery at the National Arboretum in 1961. The author was likewise surprised to hear that the first of these plants flowered and fruited in 1965, Arboretum plants differed from the true ’Sep- and all of the them flowered in 1966; in both tember’ by virtue of their rosy-red capsules. He years none flowered earlier than August 20. In wondered how this could possibly be, particu- 1966, according to National Arboretum records, larly since the older accession had been received six seed-grown plants of this accession were from the National Arboretum, the institution growing in the nursery, ranging between nine that had helped to make ’September’ widely and eleven feet in height. The records show that available in the mid-1960s. The explanation the plants varied in the size of their capsules, requires that we start at the beginning and trace but no other attributes were recorded, and none 33 The large mflorescences of the golden-ram tree produce hundreds of bmght yellow flowers and enhven any landscape m which the tree is planted. Normally, the trees flower m late June and July, but the cultivars ’September’ and ’Rose Lantern’ postpone their floral display until late August and early September when few other trees are in flower. has ever been given a cultivar name. lections. Since neither seeds nor seedlings were In a letter to March dated January 28, 1966, available, March offered root cuttings for propa- Professor McDaniel suggested that these trees, gation. In his typical fashion, Wyman penned as well as the parent trees at the University his response to this offer on the original letter of Indiana, might conform to Koelreuteria and returned it to March, commenting, "We can apiculata Rehder & Wilson. In his response that certainly try root cuttings, if you can spare September, March noted that Frederick G. them, but don’t hurt the tree." Sixteen root Meyer of the National Arboretum staff believed pieces from one or more of the six seed-grown that the trees were merely late-flowering vari- plants at the National Arboretum (NA 16548) ants of K. paniculata. Indeed, in his subsequent were subsequently sent to Wyman on March 21. monograph of the genus, Meyer (1976) placed At the Arnold Arboretum these materials were both the specific and varietal designations of accessioned as "K. pamculata-Special," and apiculata in the synonymy of K. paniculata. given accession number AA 577-66. The late Donald Wyman, then Horticulturist In 1967 McDaniel and March described and at the Arnold Arboretum, had received a carbon proposed the cultivar name ’September’ for the copy of McDaniel’s 1966 letter to March, and most floriferous of the two late-flowering trees in February of that year he wrote to March growing at the University of Indiana, which by requesting seeds or seedlings from the National that time was being propagated by softwood cut- Arboretum trees for the Arnold Arboretum col- tings. This cultivar name was duly registered 34 with the Arnold Arboretum (which at that time ter species is native to areas south of the 30th served as International Registration Authority parallel in China and is not as cold hardy as K. for cultivar names of otherwise unassigned paniculata. In 1984 the National Arboretum woody genera), and a fruiting specimen col- collections included two thirty-foot trees of K. lected from the Indiana tree on September 28, bipinnata (NA 34048) as well as four smaller 1966, was deposited in the Arboretum’s Jamaica specimens (NA 44305 Both of these accessions Plain herbarium to document the plant to had been received from the Los Angeles State which this cultivar name was applied. It was not and County Arboretum in Arcadia, California, until November, 1968, that the National Arbo- in 1972 and 1980, respectively, and the trees of retum received a plant of ’September’ vegeta- the older accession were vigorous plants with tively propagated from the University of Indiana upright crowns. Meyer (1976) had described the original. The four-inch-tall rooted cutting that color of the capsules of K. bipinnata as "rose- Professor McDaniel sent was accessioned as NA purple while young," and in some years the 31132. Four additional individuals of ’Septem- fruiting display on the National Arboretum ber’ were subsequently incorporated into the trees was truly spectacular. National Arboretum’s collections, but accession The goal of the interspecific hybridization records for these plants are missing. program was to combine the upright growth Meanwhile, only a single plant resulted at habit and reddish capsule color of Koelreuteria the Arnold Arboretum from the sixteen root bipinnata with the cold hardiness of K. pieces that had been received from the National paniculata. Because K. bipinnata normally Arboretum and accessioned under number AA flowers in late August and early September, K. 577-66. And once McDaniel and March had paniculata ’September’-in flower during the published the cultivar name ’September’, the same period-was the obvious choice for the assumption was made that the Arnold paniculata parent in the hybridization expem- Arboretum’s solitary plant represented this ments. Hybrids between the two species were clone. Consequently, its name in the indeed obtained, and McArdle and Santamour Arboretum’s records was changed from "Spe- (1987) were able to verify the hybrid status of cial" to ’September’ in 1969, and the sole repre- the seedlings using a process known as gel elec- sentative was planted adjacent to other trophoresis on isoperoxidase enzymes extracted golden-rain trees in a prominent position along from tissue at the base of leaf petioles. This pro- Meadow Road, across from the Cotinus and cess is similar to the DNA analysis of human Acer collections. One additional plant, propa- tissue that is increasingly used in today’s foren- gated in 1968 as a rooted softwood cutting from sic laboratories. The researchers analyzed hun- AA 577-66 and given accession number AA 771- dreds of hybrid plants and found only three 68, was incorporated into the Arboretum’s col- major anodal peroxidase bands-"A," "B," and lections in another prominent location, on the "C." The enzyme profile of ’September’ proved edge of Bussey Hill Road where the birch and to be "AC," while that of all six plants of K. cherry collections merge. Both of these trees bipinnata used in the hybridization program begin flowering during the last weeks of August was "B." and continue to please visitors to the Arbore- Twelve of the progeny from crossing ’Septem- tum with their bright yellow floral display into ber’ as the seed parent with K. bipinnata as the the month of September, followed by their pollen parent were identified as "true" hybrids equally handsome display of reddish pink inasmuch as they exhibited enzyme patterns of capsules into October and November. (The cap- either "AB" or "BC," with the "B" band inher- sules can be seen on the inside front cover.) ited from K. bipinnata and either the "A" or "C" band coming from K.