What is a genus? That is the question that must be answered before we can explain what happened to Coelogyne, or rather, what happened to Dendrochilum. It is best to start our explanation with an example. Take the genus Cattleya. The first Cattleya to be described was C. labiata. A reasonable guess is that everything that looks like C. labiata is a Cattleya. That means that it should have large, floppy, pinkish-purple flowers with broad petals and a trumpet-shaped lip.

André Schuiteman Photos by André Schuiteman unless stated otherwise
2-Cattleya-purpurata-was-Laelia-purpurata-photo-Andre-Schuiteman
3-Guarianthe-skinneri-was-Cattleya-skinneri-osgb5-03-120-photo-Henry-Oakeley
1-Cattleya-labiata-photo-Henry-Oakeley
5-Laelia-anceps-Wisley1-09-131-photo-Henry-Oakeley
4-Cattleya-cernua-was-Sophronitis-cernua-photo-Henry-Oakeley
7-Coelogyne-eduardii-was-Chelonistele-devogelii_MG_6612
8-Coelogyne-articulata-was-Pholidota-articulata_MG_7289
6-Laelia-itambana-photo-Joost-Riksen
10-Coelogyne-schultesii_MG_4751so4IQqz
9-Coelogyne-linearifolia-was-Dendrochilum-linearifolium_MG_8754
11-Coelogyne-blumea-was-Nabaluia-angustifolia_MG_5403
12-Dendrochilum-javierianum-photo-Gab-van-Winkel
16-Andre-Schuiteman_1500px
13-Pleione-formosana-photo-Gab-van-Winkel
a.schuiteman @ kew.org