The Identity of the African Firebush (Hamelia) in the Ornamental Nursery Trade

The neotropical shrub Hamelia patens Jacq. has been cultivated as an ornamental in the United States, Great Britain, and South Africa for many years, although only in limited numbers and as a minor element in the trade. Recently, other taxa of Hamelia have been grown and evaluated as new fl owering shrubs. The relatively recent introduction of a superior ornamental taxon of Hamelia, called the african fi rebush, has propelled this genus to greater prominence as an excellent small fl owering shrub or container plant, especially throughout the southeastern United States and in other countries such as South Africa. Initially, this fi rebush was sold as an African plant. Data from fi eld studies, herbarium specimens, and from DNA analysis of several taxa and populations of Hamelia show that the african fi rebush in southern Florida may have originated from populations of H. patens var. glabra native to southern Mexico. The original plants were taken to Europe, southern Africa, and southeastern Asia probably in the middle to late 1800s and then recently reintroduced to New World markets as a new African ornamental plant. and may be extinct. Hamelia versicolor occurs in southern Mexico and partially overlaps with the Mexican populations of H. patens. The latter is the most common of all the species and is subdivided into two varieties: H. patens var. patens and H. patens var. glabra Oersted. The widespread H. patens var. patens is found from Florida, the West Indies, and Mexico to Brazil and Argentina. Typically H. patens var. patens has red to red-orange fl owers, large ovate leaves that are moderately to densely pubescent, with large variation in leaf size, degree of pubescence, and fl ower and fruit size (Fig. 1, middle). Hamelia patens var. glabra is found in southern Mexico and disjunctly in northern South America, and has smaller, narrowly ovate pubescent leaves, a more compact habit, and yellow to yellow-orange fl owers (Fig. 1, bottom). Specimens of H. patens ‘African’ or african fi rebush were observed in 1998 in Florida at two retail ornamental nurseries and at the Fairchild Tropical Garden in Miami and in South Africa at a retail ornamental nursery and at a large wholesale nursery with a thriving export business near Pretoria, South Africa. All these The genus Hamelia (family Rubiaceae) consists of 16 species of shrubs or small trees native to lowland neotropical areas ranging from southern Florida, the West Indies, and Mexico to Brazil and Argentina (Elias, 1976). The genus is divided into two sections. Section Hamelia has strictly tubular red, orange or yellow fl owers, and Section Amphituba has yellow infundibular or sometimes broadly fl aring trumpet-shaped fl owers. Species of Hamelia have been introduced and cultivated for at least 250 years, with six species grown in England in 1839 (Sweet, 1839). In the United States, the American Exotic Nurseries in Seven Oaks, Fla., offered two species of Hamelia for sale in their 1892 catalog: H. patens with bright orange fl owers, and H. sphaerocarpa (Ruiz and Pav.) Pers. with coppery red fl owers. Both were promoted as excellent pot plants “growing freely and blooming in great profusion” (American Exotic Nurseries, 1892). In recent years, taxa of Hamelia have become important landscape plants in warmer sections of the southeastern U.S. The common and widely ranging neotropical shrub H. patens Jacq., commonly known as fi rebush or scarlet bush, has been cultivated as an ornamental for many years, although only in limited numbers and as a minor element in the trade. Although a long-lived perennial in tropical and subtropical areas, H. patens is also recommended and used as an annual bedding or container plant in more temperate zones. Hamelia patens was named a Texas Superstar by the Horticulture Department at Texas A&M University because of its excellent performance during the hot dry Texas summers (www.texassuperstar.com). It has been highly touted by the Mississippi Nursery and Landscape Association for its heat and drought tolerance and adaptation to various soil types (Winter, 2001). Hamelia patens is recommended as a low maintenance native shrub in Florida (Gilman and Meerow, 1999), and has been promoted as an attractant for hummingbirds and butterfl ies to gardeners throughout the southern U.S. as a perennial or annual (Druitt, 2002). The relatively recent introduction of a superior ornamental variety, H. patens ‘African’ or african fi rebush (Fig. 1, top), with primarily yellow to yellow-orange fl owers has propelled this genus to greater prominence as an excellent small fl owering shrub or container plant throughout the southern U.S. and in other countries such as South Africa. Hamelia is divided into two sections based on the morphology of the corolla. Hamelia section Hamelia (eight species) is characterized by a strictly tubular corolla that does not expand noticeably toward the apex, while Hamelia section Amphituba Elias (eight species) has an infundibular corolla that expands gradually or abruptly toward the apex (Elias, 1976). Hamelia papillosa Urb. is the only member from section Amphituba used in this study. It is a large shrub or small tree endemic to Jamaica and has yellow broadly campanulate to globose fl owers. The african fi rebush belongs to section Hamelia because of its tubular corolla. Species in section Hamelia that are phenotypically most similar to the african fi rebush are H. chrysantha Swartz., H. versicolor Gray, and H. patens. The rare Jamaican H. chrysantha has distinctly pedicellate fl owers. It has not been seen in recent years, Fig. 1. African fi rebush (top), Hamelia patens var. patens (middle), and H. patens var. glabra (bottom). HORTSCIENCE 39(6):1224–1226. 2004. Received for publication 2 Apr. 2003. Accepted for publication 24 Jan. 2004. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply an endorsement of these products over others not mentioned. The authors wish to thank R. Dix and J. Modlizweski for skilled technical assistance, José Luis Villasenor for help in Mexico, and Roger Hammer for fi rst bringing the African fi rebush to our attention. 7690-Breed.indd 1224 11/2/04 11:05:05 AM 1225 HORTSCIENCE VOL. 39(6) OCTOBER 2004 plants appeared phenotypically identical. They were compact shrubs with three to four small, narrowly ovate, glabrous leaves per node. The yellowish fl owers were small, narrowly tubular, and with a constriction at the base of the fl oral tube. The african fi rebush that is currently grown and sold in the southeastern U.S. is the fi rst reported African taxa of Hamelia and could represent a new taxon not previously reported to be in cultivation. Alternatively, like many earlier examples, it could represent a population that was transported far out of its natural range, maintained in cultivation, and later reintroduced to the region of its origin. The objective of our research was to determine the correct identity of the african fi rebush, its origin, and its affi nities to known existing American populations and taxa of Hamelia by examining both morphological and molecular characteristics. Materials and Methods Field and herbarium specimens. Herbarium specimens were borrowed from institutional collections of the Fairchild Tropical Garden (Miami Fla.), the National University of Mexico National Herbarium (Mexico City), the Herbarium of the National Botanical Institute (Pretoria, South Africa), the National Herbarium of the Smithsonian Institution (Washington, D.C.), and the Herbarium at the U.S. National Arboretum (Washington, D.C.). These specimens were used to determine the variability and the approximate time of introduction and establishment of species and selected cultivated forms in areas out of its native range. Fieldwork to collect herbarium specimens and seeds was conducted in South Africa, southern Florida, and southeastern Mexico in 1998. Plants were grown from seed at the U.S. National Arboretum and maintained outside in pots during the summer and inside in heated greenhouses in the winter. Voucher specimens of each of these samples were deposited in the herbarium of the U.S. National Arboretum. DNA extraction and amplifi ed fragmentlength polymorphism (AFLP) analysis. Newly expanding leaves were collected from plants and freeze-dried (Table 1). DNA was extracted from two leaves using a CTAB buffer and the QIAamp Tissue Kit (Qiagen, Inc., Valencia, Calif.) following previously published methods (Pooler, 2003). AFLP analysis (Vos et al., 1995; PE Applied Biosystems, 1996) was performed as described previously (Pooler, 2003). Completed selective reactions were analyzed on an ABI310 automated DNA sequencer with POP4 polymer. The sample was prepared by mixing 1 μL of selective reaction, 0.2 μL ROX size standard, and 9.8 μL deionized formamide. The experiments were repeated to ensure reproducibility of results. Data analysis. Markers were scored with Genotyper 2.5 software (Applied Biosystems) and assigned a value of 1 (presence of a maker) or 0 (absence of a marker) for each sample. Markers that were not scored the same in both replications of samples were assigned a score of 9 to represent missing data. Markers in which at least six of the 27 samples had missing data points were not used, nor were markers for which all samples were scored as only 0 or 9. Similarity coeffi cients between each accession were calculated using the SIMQUAL program in NTSYS-pc, version 1.70 (Rohlf, 1992), using the Dice similarity coeffi cient [2a/(2a + b + c), where a = total number of bands shared by both individuals, b = bands unique to one individual, and c = bands unique to the other individual]. These data were subjected to cluster analysis using the UPGMA method in the SAHN program of NTSYS to generate a phenogram. A cophenetic matrix was constructed and compared with the similarity matrix using the MXCOMP program to test the goodness of fi t of a cluster. Bootstrap analysis of 1000 replications was performed using WinBoot (Yap and Nelson, 1996) to estimate supports for individual clusters (Felsenstein, 1985).