Published online by Cambridge University Press: 12 June 2017
Seed germination responses to temperature and osmotic stress were determined for smallflower morningglory [Jacquemontia tamnifolia (L.) Griseb.] and seven species of Ipomoea. Cypressvine (I. quamoclit L.), willowleaf (I. wrightii Gray) and smallflower morningglory germinated and seedlings developed more slowly than the other morningglories at 16 C. Maximum germination of ivyleaf [I. hederacea (L.), Jacq. var. hederacea], entireleaf [I. hederacea (L.) Jacq. var. integriuscula Gray], pitted (I. lacunosa L.), tall [I. purpurea (L.) Roth], cotton (I. trichocarpa Ell.), and smallflower morningglories occurred in 24 h at 20 C. Cypressvine and willowleaf morningglories reached maximum germination in 24 h at 24 C. Optimal root-hypocotyl development occurred at 24 C for pitted, tall, and willowleaf morningglories, while all other species required a temperature of 28 C for maximal root-hypocotyl development in 4 days. Increasing osmotic pressure decreased or delayed germination of all morningglory species. Species tolerance to osmotic stress during germination could be ranked, most to least tolerant, as follows: ivyleaf=entireleaf>pitted=cotton>tall = willowleaf>cypressvine=smallflower. Maximum germination was delayed approximately 24 h for each 2 bar increment increase in osmotic pressure.