We present an updated monographic revision of Trithrinax, a poorly studied palm (Arecaceae) genus, including a detailed description with illustrations (including scanning electronic micrographs of the flowers) of the five accepted taxa, a compilation of common names and uses, a key to the species and varieties, a description of their ecology and updated distribution maps, and an assessment of their conservation status showing a worrying degree of threat (EN or VU) for all of them. To understand the evolutionary history of the palm tribe Cryosophileae (Coryphoideae), which includes 10 genera (i.e. Trithrinax), we performed a phylogenetic analysis with the nuclear genes RPB2 and PRK, where all recognized genera were represented. The monophyly of Chelyocarpus, Cryosophila and Trithrinax was assessed for the first time and the phylogenetic position of Trithrinax was found as basal. An analysis of the biogeographic and morphological diversification patterns showed that the origin of the tribe is the Central American region, and suggested a high degree of homoplasy for most of the characters analysed.