2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/3191We present the K-band Hubble diagram for 162 brightest cluster galaxies (BCGs) in X-ray selected clusters, 0.01<z<0.83. The sample incorporates that of Burke, Collins, & Mann (2000) and includes additional infrared data from the 2MASS extended source catalogue. We show that below z=0.1 the BCGs show no correlation with their environment, however, above z=0.1 BCGs in more X-ray luminous clusters are more uniform in their photometric properties. This suggests that there may be two populations of BCGs which have different evolutionary histories.2 pages, to appear in the proceedings of the Sesto 2001 conference on tracing cosmic evolution with galaxy clustersAstrophysicstext