The Western Australian plant family Ecdeiocoleaceae includes only three species but DNA data show them as the closest living sister-group of the Poaceae. Ecdeiocoleaceae are wind-pollinated and monoecious; spikes produce separate zones of pistillate and staminate flowers, in acropetal succession. Spikes of Ecdeiocolea have up to 45 flowers, with a sequence of zones up the spike, commonly pistillate–staminate–pistillate–staminate–pistillate, with potentially high fruit set in both of the lower pistillate zones. Rainfall in their habitats in semiarid south-western Australia is highly variable and shorter spikes with fewer zones are formed in drought conditions. Georgeantha, with fewer flowers per spike, shows the same general pattern but fewer switches. Synchrony of zonal flowering gives an effective barrier to self-pollination, a form of ‘temporal dioecy’. All spikes on many stems of a plant flower with the conspicuous white stigmas of a pistillate zone or, at a different time, all with the yellow anthers of a staminate zone. Such synchrony is between the many spikes on the plant, not between plants in a population. Features of vegetative and flowering structures and habitat are briefly mentioned.