Biotypes of Ipomoea aquatica Forssk. (Convolvulaceae) exhibit ecogeographic and cytomorphological variations in Nigeria

Abstract

Ipomoea aquatica, a vegetable cultivated and used medicinally in Asia and Africa, can become a noxious invasive weed on water and land, making navigation difficult, and displacing native species. Ecogeographic, morphological and cytological studies of the species revealed two established perennials, widely distributed and savanna-restricted ecotypes, and a sporadic annual forest type. The seeds of the annual germinated in soil after 6–8 weeks with smaller cotyledons while the perennial germinated within 2 (6) weeks with slightly larger cotyledons. They were distinguished into narrow and broad leaf morphotypes with variable leaf shapes. The wetland perennials reproduced largely by vegetative means, producing one to three flowers per inflorescence with fewer but larger fruits and seeds modified for water dispersal. The upland annual reproduced by seeds, producing 4–10 flowers per inflorescence with many but smaller fruits and dormant seeds adapted to dry conditions. The chromosome number (2n) was 30 and 28 for the perennial and annual biotypes, respectively. The mechanisms involved in the evolution of the species, its variability and spread are discussed.