Chasmanthium laxum is a perennial grass of the Poaceae family native to North America. The leaves are alternate and simple with parallel venation. The fruit is a caryopsis (dry, one-seeded, with the ovary wall and seed coat attached), and the overall root growth is fibrous.

Chasmanthium sessiliflorum is mostly morphologically similar to Chasmanthium laxum and they often grow side by side.. laxum is listed as a facultative wetland species and can be found in savanna-pocosin ecotones, sandhill-pocosin ecotones, moist hardwood swamps, bottomland hardwood forests, mesic hammocks, and other moist habitats, but this species can occur in non-wetland areas such as upland closed-canopy forests where fire is excluded, including slope forest and upland hardwood (beech-magnolia) forest, and on disturbed sites such as roadside ditches, low pinewoods, stream banks, in shallow water, and other shaded areas.

Chasmanthium laxum is shade-tolerant, enabling it to thrive under the canopy of other plants, and it primarily grows in soils such as sand, sandy loam, loam, and moist loam sand.