Abstract
Somatic chromosome numbers are reported for nine species and one variety of Callitriche (Callitrichaceae). The following new reports are included: 2n = 20 (C. nuttallii, C. marginata), 2n = 40 for one of four populations of C. heterophylla var. heterophylla, 2n = 40 (C. trochlearis), 2n = 10 (C. peploides, C. terrestris).
