The leaves are 5 to 25 cm (2 to 10 in) long, and 3 to 5 mm (0.12 to 0.20 in) wide; the upper surface is glossy dark green, flat and hairless with longitudinal veins, and the underside is shiny and smooth.

The young leaves are rolled when in bud, the auricles are small and the ligule is white and translucent, wider than it is long.

The glumes are up to three-quarters the length of the spikelet; their outer surface is finely ribbed with longitudinal veins.

[5] The flower spike of L. rigidum may become infected by a certain species of bacteria, which results in the production of corynetoxins which are toxic to livestock; ingestion of infected material causes a disease, known as annual ryegrass toxicity or annual ryegrass staggers, which is known to occur in the west and south of Australia and in South Africa.

[6] The infection is caused by the bacterium Rathayibacter toxicus, which is introduced into the grass by the nematode Anguina funesta.

Topping the pasture before grazing may prevent the condition, but the seed heads are still toxic when preserved as hay.

[7] The symptoms of poisoning are neurological, often causing a mortality rate of forty to fifty percent in infected animals.

[6] L. rigidum is susceptible to infection by ergot (Claviceps purpurea), and also by take-all fungus (Gaeumannomyces graminis) which can cause serious losses in cereal crops.

[5] Because L. rigidum has been grown as a forage crop in southern Australia since the nineteenth century and seeds readily, it grows ubiquitously in the region with large, genetically diverse populations.