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Apocynaceae
Amsonia grandiflora is a herbaceous perennial with milky sap and numerous stems arising from a long lived root. The foliage and flowers are without hairs, and the leaves vary in width, from lanceolate towards the base of the plant, to almost hair-like towards the top. The flowers are borne in terminal clusters of 5-25, commonly with 15-30 inflorescences per plant. Flowers are white tinged with lavender blue, fragrant, and salverform, with the tube from 1-2 cm in length. The two distinct ovaries that mature into narrow follicles that become papery with age and are filled with corky seeds. Peak flowering time is in April and May, with hawk moths as possible pollinators. In cultivation, pollination is conducted using a cat's whisker.
Amsonia grandiflora grows at 3,900 to 4,500 ft. on canyon bottoms in southern Arizona oak woodlands dominated by Quercus emoryi. Occasionally, populations are found on level alluvial soils that are sandy or gravelly; in other sites, they are found on rocky hillsides. During winter, plants become completely dormant, dying back to the woody crown.
The plants are now listed as 'species of concern' with the U.S. Fish and Wildlife Service, a new label for former Category 2 plants. Populations and individual plants are few in number, with only five known localities. The plants may be trampled by grazing animals, but it is unlikely that they are actually eaten, as they have milky sap and are unpalatable. Plants in cultivation at Desert Botanical Garden are avoided by rodents, and have few insect predators.
Amsonia grandiflora is easily grown from seed, and has a high reproductive potential. Cuttings are difficult, but not impossible. The time of year that cuttings are taken probably plays a major part in rooting cuttings. Plants in cultivation produce seeds readily, but must be separated from other Amsonia species to ensure that cross-pollination between species does not occur. Desert Botanical Garden has approximately 10,400 seeds in storage from three populations, and has produced 3,000 seeds in cultivation by controlled cross-pollination. Our future plans for A. grandiflora are to continue to investigate the pollination biology and horticultural requirements of the species, and to produce seed in cultivation on plants at the Garden.
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