Two New Coral Trees for the West Coast

The illustrations of these two new Erythrina hybrids are taken from Paradisus: Hawaiian Plant Watercolors by Geraldine King Tam (1999), available from the Honolulu Academy of Arts. The book’s accompanying text, where they were described as new for the first time, is by David Mabberley, perhaps best known to gardeners as the author of The Plantbook (Cambridge University Press; second edition 1997). The story of these two new trees presented here is adapted from his words in Paradisus. Gerry Tam’s original watercolors hang in the director’s office at the National Tropical Botanical Garden, Kaua’i, Hawai’i and are reproduced here with permission. Many of the other exquisite illustrations in the book are of plants familiar to West Coast gardeners.

There are just over one hundred species of Erythrina (from erythros, Greek for red) found throughout the tropical regions of the world, including twelve in Asia, thirty-one in Africa, and about seventy in the Americas. The bright red flowers of coral trees are so attractive that JC Birdwell wrote in 1938 that they were carried from their original homes by the native peoples of South America, Africa, India, Australia, and the Pacific islands. The natural distribution of many is therefore obscured; certain species may have arisen as interspecific hybrids since there appear to be few barriers to hybrid formation. The first deliberate hybrid was made in Australia: Bidwill’s coral tree (E. x bidwillii) is a cross between cockspur coral tree (E. crista-galli), a South American plant, and Cherokee bean (E. herbacea) from southern North America. Despite reports to the contrary, this hybrid seems always to be sterile; its parents are placed in different subgenera.

Bidwill’s coral tree was raised in the 1840s at Camden Park, the home of William Macarthur (1800-1882) southwest of Sydney, New South Wales, Australia. At the time William Herbert, Dean of Manchester, England, who formally described it from material sent to England by John Carne Bidwill (1815-1853; not to be confused with JC Birdwell), the first director of the Royal Botanic Gardens, Sydney; he considered it the only hybrid legume then known. Today it is recognized as the first ornamental plant developed in Australia to be illustrated in a publication (1847). These first Erythrina hybridists, the close bachelor friends, Bidwill and Macarthur, were important in pioneering plant hybridization in the Pacific. Macarthur and his family had the money, land, and greenhouse; Bidwill had the hybridizing know-how, as he came from St Thomas’s, Exeter, England, home of the great nursery of Lucombe, Pince and Co, where gladiolus hybridizing was a speciality.

The coral tree collection established in the National Tropical Botanical Garden (NTBG) on Kaua’i, Hawai’i, includes a number of hybrids raised by David Neill, whose 1984 doctoral thesis addressed the inter-relationships of the different species. Each of his two new hybrids discussed here shares a parent with Bidwill’s coral tree. Both are admirable subjects for the Mediterranean climates of the West Coast.

Malotts’ coral-tree (Erythrina x malotorum) was raised from garden stock of E. crista-galli at Waimea Arboretum, Hawai’i, sent from the NTBG, which had in turn received it from the University of Stellenbosch, South Africa; the parent was crossed with Waimea-grown swamp immortelle (E. fusca), derived from NTBG stock raised from wild-collected seeds gathered in Excuintla, Guatemala, by BA Krukoff (1898-1983). Erythrina crista-galli, the pollen parent, has inverted bird-pollinated flowers and is so nectariferous as to be called “cry-baby” in Louisiana; E. fusca, wide-spread in the tropics, is in the same subgenus although placed in a different section. The hybrid, which is sterile, commemorates Dean Waldo Malott (1898-1996), a former president of Cornell University and first president of the NTBG, and his wife Eleanor Sisson Malott, née Thrum (d. 1994). The plate is drawn from the type tree growing next to the parking lot near the Lawa’i headquarters of the NTBG. It is a first-rate ornamental tree for streets and parks, having spectacular flowers, but produces no seed and therefore no pods to clear away (a common problem with many species now in cultivation).

Like the last, Neill’s coral tree (Erythrina x neillii) is so far little-known in the nursery trade. Its long peduncles, retained long after the flowers have fallen, give a rather ungainly stag-headed look to the tree. Perhaps this hybrid will be more a plant for coral tree enthusiasts rather than in the landscape. It is named after its creator, David Neill (1953-), now associate curator at the Missouri Botanical Garden and working in Ecuador. It is a cross between Waimea-grown garden stock of E. herbacea, raised from seeds collected in Florida’s Fairchild Tropical Garden from a plant presented by Carter Bundy, and dwarf kafferboom (E. humeana), a Waimea-grown plant from the NTBG, where it had been raised from seeds collected in South Africa in 1973 and sent by Dr Millington of the University of Cardiff, Wales. The widespread E. humeana is in a different section, but the same subgenus as E. herbacea.

Coral trees are probably all pollinated by birds. Those in Malaysia, for example, where there are no hummingbirds, have long flower stalks like those of E. x neillii, acting as perches for the non-hovering sunbirds that are their pollinators. Many American species have small tubular flowers with nectar high in sucrose and low in amino-acids, a combination associated with pollination by long-billed hummingbirds; the species visited by passerine birds have flowers that are twisted back towards the peduncle, as in E. crista-galli, and the nectar is low in sucrose but high in amino-acids. In the hummingbird-pollinated species, there is insufficient caloric value in the nectar of flowers open on any one day to sustain a single bird’s energy, so the bird is forced to visit at least one other tree, thus effecting cross-pollination. In monsoon climates, Erythrina species open their flowers in the dry season and provide an important source of water for pollinating birds, as well as for squirrels. Extra-floral nectaries attract ants, which act as guards by keeping off other predators; some species offer their twigs as homes for the ants.