Pacific Plant Promotions: Catophractes alexandri

By: Kathy Musial

Kathy Musial is curator of living collections at the Huntington Botanical Gardens where she has worked for more than twenty-five…

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Last year, while packing for the move into the Huntington’s new Botanical Center, I was rummaging through the packets, envelopes, and bags of seed that were stored in the refrigerator. Among these was a rumpled brown paper bag with the scribbled name “Catophractes alexandri”. I was amused to find that after eighteen years, we still had the original bag with some of the seed sent to us in 1983. These had arrived, along with other treasures, from plant collector John Lavranos, who has blessed the Huntington Botanical Gardens over many years with seeds from his travels in Africa and elsewhere.

Catophractes alexandri. Author’s photographs

Catophractes alexandri. Author’s photographs

Catophractes alexandri is a monotypic genus in the Bignoniaceae, the mostly tropical trumpet vine family to which other familiar cultivated plants such as Tabebuia, Jacaranda, and Tecomaria belong. Commonly known as trumpet thorn, it is found in southern Africa from Angola through Namibia and Botswana to Zimbabwe and the Transvaal. It inhabits arid regions of scrubby or thornveld vegetation. Typically found on lime-rich soils or limestone outcrops, it sometimes forms pure colonies, said to be a memorable sight when in full bloom. Springbok and zebra graze the foliage, kudu relish the flowers and young fruits, and rhino browse the branches.

Trumpet thorn is a shrub, three to six feet tall, with multiple stems arching out from the base to form an open, curiously sculptural habit; it rarely becomes a small tree of ten feet in height. The spine-tipped branchlets, up to two inches long, are a distinctive feature of the shrub, developing as the plants mature. These are in opposite pairs; on more mature plants each successive pair along the stem is at a 90° angle to the previous one, forming a geometric pattern best appreciated when viewed directly down the length of the stem. Foliage and flowers arise from axils below the spine tips, a trait from which the name Catophractes (Greek for “below the spines”) is derived. The silvery gray leaves, usually in fascicles of three, are softly tomentose and contrast nicely with the shiny chocolate-brown stems. Foliage of young plants is green. Each leaf is oblong, typically about an inch long and half as wide, with scalloped margins; leaves are puckered above from the impressed veins.

Flowers and foliage of Catophractes alexandri

Flowers and foliage of Catophractes alexandri

Plants blossom after the sporadic rains, which, in habitat, can occur at any time of year; in cultivation flowers appear in summer. Usually occurring in pairs toward the ends of the branches, the solitary flowers are snow-white, sometimes suffused with pink, the long buds emerging from the fuzzy reddish pink inch-long calyx like lipstick from its tube. The bud unfurls into a frilly five-lobed trumpet, two inches across, whose long, yellow-throated tube is a clue that hawk moths are the pollinators. In my experience the flowers are rather ephemeral: whenever I have tried to photograph them, one falls to the ground milliseconds before I click the shutter. If the pollinators are successful, pendulous, warty, three-inch capsules appear that split open into boat-shaped halves, the papery seeds blowing away on the slightest breeze. The empty woody capsules remain attached to the plant, rattle in the wind—a familiar desert song to nearby inhabitants—and give rise to another common name, rattle tree.

Trumpet thorn is a plant that has rarely if ever been cultivated, so information on its requirements is lacking in reference books and is based on extrapolation from its habitat and experience here at the Huntington in San Marino, California. It is ideally suited to arid regions receiving limited frost, although a young plant in our Subtropical Garden, planted just a few months before the 1990 freeze, survived that meteorological event without injury. Full sun is needed, and the silvery aspect shows up to best advantage against a dark or solid green background. Lean, slightly alkaline sandy soil is recommended, though heavier soils will be all right if drainage is fast, as might be found on a slope. Trumpet thorn tolerates weekly watering here; however, established plants should need only a minimum of water, but on a regular basis during the warmer seasons for best flowering. Pruning is generally unnecessary, but, if warranted, branches should be completely removed at the base. Plants can be grown in containers using a soil mix prepared for cacti. Propagation is by seed, which are surprisingly long-lived and sprout within three days after sowing. The plants available through this Pacific Plants Promotion were recently grown by staff at the Huntington from the original, now eighteen-year-old seed.

Catophractes alexandri will make a distinctive and unusual addition to the garden. To order one, use the PPP reservation card (opposite page 64) for details. See Pacific Horticulture, January 2000, for a description of the Pacific Plant Promotions program.