This is considered native to a large region of western Eurasia, and it is now widely scattered across temperate North America (F, FNA 24). The taxon may be better treated as P. pratensis ssp. angustifolia (L.) Lej., as in FNA. It is highly variable, with 2n = 28 to 83, but low ploidies predominate. In Ky. such plants form a locally abundant component of old pastures, especially on subxeric sites within the Bluegrass region, and they often suggest native status. Gm noted: "Bluegrass is a variable plant. In open pastures where the turf is long-established it is often of a pure green color, with narrow, slightly folded blades..." P. angustifolia differs from typical pratensis in their more densely tufted habit (less turf-forming) and folded to involute leaf blades that are only 0.4-1 mm wide, even in well-grown plants (versus up to 1.5-4.5 mm). Also blades often have sparse hairs (versus rarely). Lemmas tend to be shorter (ca. 2.5-3.5 mm versus 2.8-4.3 mm). The cultivar known as Kenblue may be derived in large part from these plants, since it has leaves about half as wide as typical pratensis (T. Phillips, pers. comm.). This cultivar was developed by R.C. Buckner in the 1960s (Univ. of Ky.. Agronomy Notes, 1968, Vol. 1, No. 8, 3 pages), but no morphological description has been published. In Britain, its ecology has been summarized as follows (BSBI 2022): "A rhizomatous perennial grass of dry grassland, wall-tops, rough ground and railway embankments, typically on relatively infertile chalky, sandy or gravelly soils, but also clays that dry out in the summer, and thus able to persist in very xerophytic habitats. In parts of southern England it often occurs in partial shade under beech trees. It flowers and sets seed earlier than other members of the P. pratensis group. Predominantly lowland." See also Barling (1959).