Background and Aims Zosterophyllum, a diverse genus in the global flora spanning the Silurian to Devonian periods, has been documented extensively through qualitative morphological descriptions. Here, we describe a new Zosterophyllum species and introduce quantitative approaches to elucidate evolutionary patterns of diversity and morphological disparity in this genus.Methods Compression specimens from the upper Silurian (Pridoli) in West Junggar, Xinjiang, China were studied through d & eacute;gagement and macro/microphotography. Morphological and occurrence data of all 26 known Zosterophyllum species were collected and analysed for diversity and disparity using ImageJ, R, PAST and PyRate software.Key Results A new species, Zosterophyllum mangkeluense sp. nov. was recognized, characterized by H-shaped creeping and smooth erect axes, terminal uniformly elongated and relatively compacted spikes, with helically arranged fan-shaped or elliptical sporangia with short stalks and unequal valves. The diversity of Zosterophyllum species peaked during the Pragian interval of the Early Devonian, coinciding with the maximum occupation of their morphospace, the principal expansion of which reflected increases in diversity of both whole-plant and sporangium morphology and pre-dated the increase in diversity.Conclusions Asynchronous and decoupled patterns of change in diversity and morphological disparity among Zosterophyllum species are supported. Increased disparity in reproductive morphology is considered to be closely associated with changes in Zosterophyllum species diversity.