Greek a — not, geras — old, as the flowers last for a long time.
Annual or perennial herbs. Stems often spreading and rooting at nodes. Leaves along stems, opposite or sometimes alternate, entire or toothed. Capitula diskoid, small, in tassel-like clusters. Involucral bracts in 1 or 2 overlapping rows, more or less equal. Receptacle with or without scales, conical. Florets all bisexual, tubular. Achenes 4- or 5-ribbed, glabrous or with short hairs on ribs. Pappus a crown, of 5 or 6 scales or short bristles, or absent.
Small capitula in tassel-like clusters; glandular dots on leaf undersides; florets all tubular, mostly blue, pink or white.
44 species from C and S America and the W Indies.
Source: (2002). Asteraceae. In: . Horticultural Flora of South-eastern Australia. Volume 4. Flowering plants. Dicotyledons. Part 3. The identification of garden and cultivated plants. University of New South Wales Press.