Yellow oat-grass (Trisetum flavescens) is primarily a species of limestone grassland and so its stronghold in Dorset is, not surprisingly then, the Purbeck cliffs and ridge-way and here it is quite common. It can be found on chalk grasslands too.
Although quite distinctly a member of the oat family its flower head remains fairly upright whereas in the wild oat species the flower/seed heads are found at the end of horizontal thing stems. These flowers heads have a yellow, almost golden, tinge even when new which gives it is common name of course. It is a medium height grass growing to about two feet tall in loose tufts (ie: several stems from a single root) and it has a single, long thin leaf that bends away from the main stem.
Growing on calcareous soils it absorbs some of the calcium into its structure and this makes it toxic to livestock who, in turn, can absorb excess amounts of calcium into their organs which causes various health problems.