Chromosome numbers of T. verticillata Forman have been preliminarily found to be n = c. 21 and 2n = 40, 42, 44. They require future verification based on the study of more collections from its geographical range of distribution. The haploid chromosome numbers in Fagaceae so far known are 12 in most of the genera and 13 in Nothofagus. The number of c. 21 for Trigonobalanus is unique and new in this family. Irregularities of chromosome behaviour during meiosis, such as secondary association, lagging, precocious separation of chromosomes, etc. have been observed.